BASIN EXPLORATION INC
PREM14A, 2000-11-22
CRUDE PETROLEUM & NATURAL GAS
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<PAGE>   1

                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

                                  SCHEDULE 14A
                                 (RULE 14A-101)

                    INFORMATION REQUIRED IN PROXY STATEMENT
                            SCHEDULE 14A INFORMATION

PROXY STATEMENT PURSUANT TO SECTION 14(a) OF THE SECURITIES EXCHANGE ACT OF 1934

     Filed by the Registrant [X]
     Filed by a Party other than the Registrant [ ]
     [X] Preliminary Proxy Statement
     [ ] Confidential, for Use of the Commission Only (as permitted by Rule
     14a-6(e)(2))
     [ ] Definitive Proxy Statement
     [ ] Definitive Additional Materials
     [ ] Soliciting Material Under Rule 14a-12

                                  JOINT FILING BY:
                              STONE ENERGY CORPORATION
                               BASIN EXPLORATION, INC.
--------------------------------------------------------------------------------
              (NAME OF REGISTRANTS AS SPECIFIED IN THEIR CHARTERS)

Payment of Filing Fee (Check the appropriate box):
     [ ] No fee required.
     [X] Fee computed on table below per Exchange Act Rules 14a-6(i)(l) and
         0-11.

     (1) Title of each class of securities to which transaction applies:

         Common Stock, $0.01 par value per share, of Basin Exploration, Inc.
--------------------------------------------------------------------------------
     (2) Aggregate number of securities to which transaction applies:

         18,532,889 shares of Basin Exploration, Inc. Common Stock
--------------------------------------------------------------------------------
     (3) Per unit price or other underlying value of transaction computed
pursuant to Exchange Act Rule 0-11 (Set forth the amount on which the filing fee
is calculated and state how it was determined):

              The proposed maximum aggregate value of the transaction of
         $399,036,266 was calculated in accordance with Rule 0-11(a)(4) and (c)
         promulgated under the Securities Exchange Act of 1934, as amended,
         based on the average of the high and low sale price per share of Basin
         Exploration, Inc. Common Stock on the Nasdaq National Market on
         November 20, 2000 multiplied by 18,532,889, the outstanding number of
         shares of Basin Exploration, Inc. Common Stock.
--------------------------------------------------------------------------------
     (4) Proposed maximum aggregate value of transaction:

         $399,036,266
--------------------------------------------------------------------------------
     (5) Total fee paid:

         $79,807
--------------------------------------------------------------------------------

     [ ] Fee paid previously with preliminary materials.

     [ ] Check box if any part of the fee is offset as provided by Exchange Act
Rule 0-11(a)(2) and identify the filing for which the offsetting fee was paid
previously. Identify the previous filing by registration statement number, or
the Form or Schedule and the date of its filing.

     (1) Amount Previously Paid:

--------------------------------------------------------------------------------
     (2) Form, Schedule or Registration Statement No.:

--------------------------------------------------------------------------------
     (3) Filing Party:

--------------------------------------------------------------------------------
     (4) Date Filed:

--------------------------------------------------------------------------------
<PAGE>   2

                    SUBJECT TO COMPLETION, NOVEMBER 22, 2000

STONE LOGOBASIN LOGO

                 PROPOSED MERGER -- YOUR VOTE IS VERY IMPORTANT

     Stone Energy Corporation and Basin Exploration, Inc. have agreed on a
merger transaction involving our two companies. Before we can complete the
merger, we must obtain the approval of our companies' stockholders. We are
sending you this joint proxy statement/prospectus to ask you to vote in favor of
the merger transaction and related matters.

     In the merger, stockholders of Basin will be entitled to receive .3974 of a
share of Stone common stock in return for each share of Basin common stock they
currently own. On             , 2000, the closing price of Stone common stock
was $     per share and the closing price of Basin common stock was $     per
share. We encourage you to obtain more recent quotations. Outstanding shares of
Stone common stock will remain unchanged in the merger. The shares of Stone
common stock, including the shares of Stone common stock issued to stockholders
of Basin as a result of the merger, will continue to be listed on the New York
Stock Exchange, or NYSE, under the trading symbol "SGY." Shares of Basin common
stock, which are currently traded on the Nasdaq National Market under the
trading symbol "BSNX," will be delisted if the merger is consummated.

     We will each hold a special meeting of our stockholders to consider and
vote on the merger proposal. At Stone's special meeting it will ask its
stockholders to consider and vote on an amendment to Stone's certificate of
incorporation to increase the authorized shares of Stone's common stock from
25,000,000 shares to             shares and on the issuance of shares of Stone
common stock in the merger. Approval of the proposal to amend Stone's
certificate of incorporation is a prerequisite to approval of the proposal for
the share issuance. At Basin's special meeting it will ask its stockholders to
consider and vote on the merger agreement and the merger. Completion of the
merger requires both of these stockholder approvals. PLEASE CAST YOUR VOTE FOR
YOUR SPECIAL MEETING BY COMPLETING, SIGNING AND DATING YOUR PROXY CARD AND
RETURNING IT IN THE ENCLOSED ENVELOPE, OR IN THE CASE OF BASIN STOCKHOLDERS, YOU
MAY ALSO VOTE BY FOLLOWING THE INTERNET OR TELEPHONE INSTRUCTIONS ON THE PROXY
CARD.

     The dates, times and places of the stockholders' meetings are as follows:

<TABLE>
<S>                                    <C>
FOR STONE STOCKHOLDERS:                FOR BASIN STOCKHOLDERS:
                           , 2000      , 2000
                    a.m., C.S.T.       a.m., M.S.T.
</TABLE>

     This document is a prospectus of Stone relating to the issuance of shares
of Stone's common stock in connection with the merger and a proxy statement for
both Stone and Basin to use in soliciting proxies for our special meetings. It
contains answers to frequently asked questions and a summary description of the
merger (beginning on page 1), followed by a more detailed discussion of the
merger and related matters. YOU SHOULD ALSO CONSIDER THE MATTERS DISCUSSED UNDER
"RISK FACTORS" COMMENCING ON PAGE 19 OF THE ENCLOSED JOINT PROXY
STATEMENT/PROSPECTUS. We urge you to review carefully this entire document.

<TABLE>
<S>                                 <C>
James H. Stone                      Michael S. Smith
Chairman of the Board               Chairman of the Board
Stone Energy Corporation            Basin Exploration, Inc.
</TABLE>

     NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES
COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE
ADEQUACY OR ACCURACY OF THIS JOINT PROXY STATEMENT/PROSPECTUS. ANY
REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

     THIS JOINT PROXY STATEMENT/PROSPECTUS IS DATED             , 2000, AND IS
BEING FIRST MAILED TO STOCKHOLDERS ON OR ABOUT             , 2000.
<PAGE>   3

                      REFERENCES TO ADDITIONAL INFORMATION

     This document incorporates important business and financial information
about Stone and Basin that is not included in or delivered with this document.
This information is available without charge to you upon written or oral request
at the applicable company's address and telephone number listed on page 5. See
also "Where You Can Find More Information" beginning on page 88. To obtain
timely delivery, you must request the information no later than             ,
2000.
<PAGE>   4

                            BASIN EXPLORATION, INC.
                           1670 BROADWAY, SUITE 2800
                             DENVER, COLORADO 80202

                             ---------------------

                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                                          , 2000

                             ---------------------

To the Stockholders of
BASIN EXPLORATION, INC.:

     A Special Meeting of Stockholders of Basin Exploration, Inc. will be held
at           , at   a.m., M.S.T., on             , 2000 for the following
purposes:

          (1) To consider and vote upon a proposal to approve the merger
     agreement among Stone Energy Corporation, Partner Acquisition Corp., which
     is a newly-formed, wholly-owned subsidiary of Stone Energy Corporation, and
     Basin Exploration, Inc., and the transactions contemplated by the merger
     agreement, including the merger; and

          (2) To transact such other business as may properly come before the
     meeting or any adjournment thereof.

     Holders of record of shares of Basin common stock at the close of business
on           , 2000 are entitled to notice of and to vote at the meeting and any
adjournment thereof.

     You are cordially invited to attend the meeting. YOUR VOTE IS IMPORTANT TO
ENSURE YOUR REPRESENTATION AT THE MEETING. WHETHER OR NOT YOU ARE PLANNING TO
ATTEND THE MEETING, YOU ARE URGED TO COMPLETE, DATE AND SIGN THE ENCLOSED PROXY
CARD AND RETURN IT PROMPTLY. THE DELIVERY OF THE PROXY DOES NOT PRECLUDE YOU
FROM VOTING IN PERSON IF YOU ATTEND THE MEETING. IF YOU DO NOT VOTE, IT WILL
HAVE THE SAME EFFECT AS VOTING AGAINST THE MERGER AGREEMENT AND THE MERGER. No
additional postage is necessary if mailed in the United States. Stockholders of
record can also vote their shares using the Internet or the telephone.
Instructions for using these convenient services are set forth on the enclosed
proxy card. If you desire to revoke your proxy, you may do so at any time before
the vote as discussed on page 25 of this joint proxy statement/ prospectus.

     After careful consideration, the Basin board of directors has determined
that the merger agreement and the transactions contemplated by it are in the
best interests of Basin and its stockholders. Accordingly, the members of the
Basin board of directors unanimously recommend that stockholders vote to approve
the merger agreement and the transactions contemplated by it, including the
merger, at the special meeting.

     Please do not send any Basin stock certificates at this time. If the merger
is approved by the stockholders of Basin, and if the other conditions to the
merger are satisfied or waived, forms to be used to exchange your shares of
Basin common stock for shares of Stone common stock will be mailed to you.

                                            BY ORDER OF THE BOARD OF DIRECTORS

                                            HOWARD L. BOIGON
                                            Secretary

Denver, Colorado
            , 2000
<PAGE>   5

                            STONE ENERGY CORPORATION
                          625 EAST KALISTE SALOOM ROAD
                           LAFAYETTE, LOUISIANA 70508

                             ---------------------

                   NOTICE OF SPECIAL MEETING OF STOCKHOLDERS
                                           , 2000

                             ---------------------

To the Stockholders of
STONE ENERGY CORPORATION:

     A Special Meeting of Stockholders of Stone Energy Corporation will be held
at           , at   a.m., C.S.T., on             , 2000 for the following
purposes:

          (1) To consider and vote upon a proposal to amend Stone's certificate
     of incorporation to increase the authorized shares of Stone's common stock
     from 25,000,000 shares to             shares;

          (2) To consider and vote upon a proposal to approve the issuance of
     the shares of Stone common stock to be received by Basin Exploration, Inc.
     stockholders in the proposed merger between Basin and Partner Acquisition
     Corp., a newly-formed, wholly-owned subsidiary of Stone Energy Corporation;
     and

          (3) To transact such other business as may be properly brought before
     the meeting and any adjournments thereof.

     Approval of the proposal to amend Stone's certificate of incorporation is a
prerequisite to approval of the proposal for the share issuance.

     Holders of record of shares of Stone common stock at the close of business
on           , 2000 are entitled to notice of and to vote at the meeting and any
adjournment thereof.

     You are cordially invited to attend the meeting. YOUR VOTE IS IMPORTANT TO
ENSURE YOUR REPRESENTATION AT THE MEETING. WHETHER OR NOT YOU ARE PLANNING TO
ATTEND THE MEETING, YOU ARE URGED TO COMPLETE, DATE AND SIGN THE ENCLOSED PROXY
CARD AND RETURN IT PROMPTLY. THE DELIVERY OF THE PROXY DOES NOT PRECLUDE YOU
FROM VOTING IN PERSON IF YOU ATTEND THE MEETING. IF YOU DO NOT VOTE, IT WILL
HAVE THE SAME EFFECT AS VOTING AGAINST THE AMENDMENT TO STONE'S CERTIFICATE OF
INCORPORATION AND THE ISSUANCE OF SHARES OF STONE COMMON STOCK IN CONNECTION
WITH THE MERGER. No additional postage is necessary if mailed in the United
States. If you desire to revoke your proxy, you may do so at any time before the
vote as discussed on page 25 of this joint proxy statement/prospectus.

     The Stone board of directors has determined that the terms of the merger
agreement and the transactions contemplated by it are in the best interests of
Stone and its stockholders. The members of the Stone board of directors
participating in the board decision on the transaction unanimously recommend
that stockholders vote at the special meeting to approve the amendment to
Stone's certificate of incorporation to increase the authorized shares of
Stone's common stock and the issuance of Stone common stock in connection with
the merger. One of Stone's directors did not participate in the board decision
on the transaction due to an affiliation with Basin's financial advisor in this
transaction.

                                            BY ORDER OF THE BOARD OF DIRECTORS

                                            ANDREW L. GATES, III
                                            Secretary

Lafayette, Louisiana
            , 2000
<PAGE>   6

                               TABLE OF CONTENTS

<TABLE>
<S>                                                           <C>
QUESTIONS AND ANSWERS ABOUT THE MERGER......................     1
SUMMARY.....................................................     5
RISK FACTORS................................................    19
  The market value of shares of Stone common stock that
     Basin stockholders receive in the merger will vary as a
     result of the fixed exchange ratio and possible stock
     price fluctuations.....................................    19
  There are uncertainties in integrating our business
     operations.............................................    19
  Significant charges and expenses will be incurred as a
     result of the merger...................................    19
  Stone's certificate of incorporation and by-laws have
     provisions that discourage corporate takeovers and
     could prevent stockholders from realizing a premium on
     their investment.......................................    19
  Some of Basin's directors and officers have interests in
     the merger that are different from your interests......    20
CAUTIONARY STATEMENT ABOUT FORWARD-LOOKING STATEMENTS.......    21
THE SPECIAL MEETINGS........................................    22
  Information About the Special Meetings and Voting.........    22
  Time and Place of the Special Meetings....................    22
  Shares Beneficially Owned by Stone and Basin Directors and
     Executive Officers as of the Record Date...............    23
  Vote Necessary at the Special Meetings to Approve Stone
     and Basin Proposals....................................    23
  Voting by Proxy...........................................    24
  How to Vote by Proxy......................................    24
  Revoking Your Proxy.......................................    25
  Other Voting Matters......................................    25
  Other Business; Adjournments and Postponements............    25
THE MERGER..................................................    26
  Background of the Merger..................................    26
  Reasons for the Merger; Recommendations of the Board of
     Directors..............................................    29
  Opinion of Basin's Financial Advisor......................    33
  Opinion of Stone's Financial Advisor......................    37
  Interests of Certain Persons in the Merger................    46
  Accounting Treatment......................................    50
  Regulatory Approvals......................................    50
  Legal Proceedings.........................................    50
  Appraisal Rights..........................................    50
  Federal Securities Law Consequences.......................    51
  U.S. Federal Income Tax Consequences Of The Merger........    51
THE MERGER AGREEMENT........................................    53
  The Merger................................................    53
  Merger Consideration......................................    53
  Exchange Procedures.......................................    53
  Representations and Warranties............................    54
  Covenants and Agreements..................................    55
  Conditions................................................    63
  Termination...............................................    64
  Effect of Termination.....................................    65
  Termination Fees..........................................    65
  Costs and Expenses........................................    66
  Amendment and Waiver......................................    66
</TABLE>

                                        i
<PAGE>   7
<TABLE>
<S>                                                           <C>
VOTING AGREEMENTS...........................................    67
  Basin Voting Agreement....................................    67
  Stone Voting Agreement....................................    67
THE COMPANIES...............................................    68
  Business of Basin Exploration, Inc. ......................    68
  Business of Stone Energy Corporation......................    68
  Partner Acquisition Corp..................................    69
STONE ENERGY CORPORATION CONDENSED UNAUDITED PRO FORMA
  COMBINED FINANCIAL STATEMENTS.............................    70
COMPARISON OF STOCKHOLDERS' RIGHTS..........................    79
PROPOSED AMENDMENT TO STONE'S CERTIFICATE OF
  INCORPORATION.............................................    86
LEGAL AND TAX MATTERS.......................................    86
EXPERTS.....................................................    86
INDEPENDENT PUBLIC ACCOUNTANTS..............................    87
OTHER MATTERS...............................................    87
STOCKHOLDER PROPOSALS.......................................    87
WHERE YOU CAN FIND MORE INFORMATION.........................    88
</TABLE>

                                       ii
<PAGE>   8

                                    ANNEXES

<TABLE>
<S>                                    <C>
Annex A..............................  Agreement and Plan of Merger, dated as of October 28, 2000,
                                       by and among Stone Energy Corporation, Partner Acquisition
                                         Corp. and Basin Exploration, Inc.
  Exhibit A1.........................  Form of Basin Voting Agreement by and among Stone Energy
                                         Corporation, Basin Exploration, Inc. and the Basin
                                         Stockholders listed on the signature page thereto
  Exhibit A2.........................  Form of Stone Voting Agreement by and among Stone Energy
                                         Corporation, Basin Exploration, Inc. and the Stone
                                         Stockholders listed on the signature page thereto
  Appendix 1.04(c)...................  Non-Competition Term Sheet
Annex B..............................  Opinion of Goldman, Sachs & Co., dated October 28, 2000
Annex C..............................  Opinion of Merrill Lynch & Co., dated October 28, 2000
Annex D..............................  Proposed Amendment to Stone's Certificate of Incorporation
</TABLE>

                                       iii
<PAGE>   9

                     QUESTIONS AND ANSWERS ABOUT THE MERGER

Q:    WHAT WILL HAPPEN IN THE MERGER?

A:    The proposed merger will combine the businesses of Stone and Basin. To
      combine the companies, a subsidiary of Stone will merge into Basin. As a
      result, Basin will become a wholly-owned subsidiary of Stone. Basin
      stockholders will become Stone stockholders and will own approximately 29%
      of the shares of Stone common stock that are outstanding after the merger.
      Current Stone stockholders will own the remaining approximately 71%. The
      merger agreement, which is a contract among Stone, Basin and a subsidiary
      of Stone, is attached to this joint proxy statement/prospectus as Annex A.
      You should read the merger agreement carefully in its entirety because it
      is the legal document setting forth the parties' rights.

Q:    WHY ARE STONE AND BASIN PROPOSING THE MERGER?

A:    Our companies are proposing the merger because we believe that the
      combined company will be able to compete more effectively for and secure
      growth opportunities. We believe that the companies have complementary
      skills, and that the combined company's portfolio of prospects affords a
      greater diversity of risk, flexibility and opportunity than either
      company's portfolio individually. Please read the more detailed
      description of our reasons for the merger on pages 29 through 32.

Q:    WHAT WILL THE NEW COMPANY BE CALLED AND WHERE WILL IT BE
      HEADQUARTERED?

A:    The combined company will be called "Stone Energy Corporation" and will be
      headquartered in Lafayette, Louisiana.

Q:    WHAT WILL HAPPEN TO BASIN SHARES AND OPTIONS IN THE MERGER?

A:    Basin common stockholders will receive .3974 of a share of Stone common
      stock for each share of Basin common stock they own. Basin stockholders
      also will receive cash for any fractional Stone shares they would be
      otherwise entitled to in the merger. The shares of Stone common stock
      received in the merger will be listed on the NYSE under the ticker symbol
      "SGY." Options to purchase Basin common stock will be converted into
      options to purchase shares of Stone common stock based on the same
      exchange ratio as applies to the conversion of Basin common stock.

Q:    WHAT WILL HAPPEN TO SHARES OF STONE COMMON STOCK IN THE MERGER?

A:    Nothing. Each outstanding share of Stone common stock will remain
      outstanding as a share of Stone common stock.

Q:    WHEN ARE THE SPECIAL STOCKHOLDERS' MEETINGS?

A:    Each company's special meeting of stockholders will take place on
                  , 2000. The time and location of each special meeting is
      specified on the cover page of this document.

Q:    WHAT WILL HAPPEN AT THE SPECIAL STOCKHOLDERS' MEETINGS?

A:    At the Basin special meeting, Basin common stockholders will vote on the
      merger agreement and the transactions contemplated by the merger
      agreement, including the merger. At the Stone special meeting, Stone
      stockholders will vote on an amendment to Stone's certificate of
      incorporation to increase the authorized shares of Stone's common stock
      from 25,000,000 shares to             shares and on the issuance of shares
      of Stone common stock in the merger. We cannot complete the merger unless,
      among other things, Basin common stockholders vote to approve the merger
      agreement and Stone stockholders vote to approve the amendment to Stone's
      certificate of incorporation and the share issuance. Approval of the
      proposal to amend Stone's certificate of incorporation is a prerequisite
      to approval of the proposal for the share issuance.

                                        1
<PAGE>   10

Q:     WHAT DO I NEED TO DO TO VOTE?

A:    Mail your signed proxy card in the enclosed return envelope or, in the
      case of Basin stockholders, you also may vote by Internet or by telephone,
      in each case as soon as possible so that your shares may be represented at
      your special meeting. In order to assure that we obtain your vote, please
      vote as instructed on your proxy card even if you currently plan to attend
      your special meeting in person. THE MEMBERS OF THE BASIN BOARD OF
      DIRECTORS UNANIMOUSLY RECOMMEND THAT BASIN STOCKHOLDERS VOTE FOR THE
      MERGER AGREEMENT AND THE TRANSACTIONS CONTEMPLATED BY THE MERGER
      AGREEMENT, INCLUDING THE MERGER. THE MEMBERS OF THE STONE BOARD OF
      DIRECTORS PARTICIPATING IN THE BOARD DECISION ON THE TRANSACTION
      UNANIMOUSLY RECOMMEND THAT STONE STOCKHOLDERS VOTE AT THE SPECIAL MEETING
      TO APPROVE THE AMENDMENT TO STONE'S CERTIFICATE OF INCORPORATION TO
      INCREASE THE AUTHORIZED SHARES OF STONE'S COMMON STOCK AND THE ISSUANCE OF
      STONE COMMON STOCK IN CONNECTION WITH THE MERGER. ONE OF STONE'S DIRECTORS
      DID NOT PARTICIPATE IN THE BOARD DECISION ON THE TRANSACTION DUE TO AN
      AFFILIATION WITH BASIN'S FINANCIAL ADVISOR IN THIS TRANSACTION.

Q:    ARE THERE RISKS ASSOCIATED WITH THE MERGER THAT I SHOULD CONSIDER IN
      DECIDING HOW TO VOTE?

A:    Yes. There are risks associated with all business combinations, including
      the merger. In particular, you should be aware that the number of shares
      of Stone common stock that Basin stockholders will receive is fixed and
      will not change as the market prices of shares of Basin common stock and
      shares of Stone common stock fluctuate in the period before the merger.
      Accordingly, the value of the shares of Stone common stock that Basin
      stockholders will receive in return for their shares of Basin stock may be
      either less than or more than the value of the shares of Stone common
      stock as of the date of the merger agreement or the date of this joint
      proxy statement/prospectus. There also are a number of other risks that
      are discussed in this document and in other documents incorporated by
      reference in this document. PLEASE READ WITH PARTICULAR CARE THE MORE
      DETAILED DESCRIPTION OF THE RISKS ASSOCIATED WITH THE MERGER ON PAGES 19
      THROUGH 20.

Q:    WHEN DO YOU EXPECT TO COMPLETE THE MERGER?

A:    We expect to complete the merger as quickly as possible once all the
      conditions to the merger, including obtaining the approvals of our
      stockholders at the special meetings, are fulfilled or waived. Fulfilling
      some of these conditions, such as receiving certain governmental
      clearances or approvals, is not entirely within our control. We currently
      expect to complete the merger in        .

Q:    SHOULD I SEND IN MY BASIN STOCK CERTIFICATES NOW?

A:    No. After the merger is completed, we will send written instructions to
      Basin stockholders that explain how to exchange Basin stock certificates
      for Stone stock certificates. We will also send a letter of transmittal
      that must be executed by Basin stockholders. Please do not send in any
      Basin stock certificates until you receive these written instructions and
      the letter of transmittal.

Q:    HOW DO I VOTE MY SHARES IF MY SHARES ARE HELD IN "STREET NAME"?

A:    You should vote this proxy in accordance with the instructions provided to
      you by your broker. Your broker will not vote your shares unless the
      broker receives appropriate instructions from you.

                                        2
<PAGE>   11

Q:    MAY I CHANGE MY VOTE EVEN AFTER RETURNING A PROXY CARD?

A:    Yes. If you are a Basin stockholder and want to change your vote, you may
      do so at any time before the Basin special meeting by sending to the
      Secretary of Basin a proxy with a later date or by voting again by
      Internet or telephone. Alternatively, you may revoke your proxy by
      delivering to the Secretary of Basin a written revocation prior to the
      Basin special meeting or by voting in person at the Basin special meeting.
      Similarly, if you are a Stone stockholder and want to change your vote,
      you may do so at any time before the Stone special meeting by sending to
      the Secretary of Stone a proxy with a later date. Alternatively, you may
      revoke your proxy by delivering to the Secretary of Stone a written
      revocation prior to the Stone special meeting or by voting in person at
      the Stone special meeting. Basin stockholders that require assistance in
      changing or revoking a proxy should contact Corporate Stock Transfer,
      Inc., Basin's transfer agent for the merger, at (303) 282-4800. Stone
      stockholders that require assistance in changing or revoking a proxy
      should contact ChaseMellon Stockholder Services LLC, Stone's solicitation
      agent for the merger, at (800) 635-9270. ChaseMellon's website can be
      found at www.chasemellon.com.

Q:    WILL BASIN STOCKHOLDERS BE ABLE TO TRADE THE STONE COMMON STOCK
      THAT THEY RECEIVE IN THE MERGER?

A:    Yes. The Stone Common Stock will be listed on the New York Stock Exchange
      under the symbol "SGY". However, persons who are affiliates of Basin will
      not be able to sell the Stone shares received in the merger unless they
      comply with Rule 145 under the Securities Act and certain restrictions
      under accounting rules relating to pooling-of-interests accounting
      treatment. Affiliates of Stone will also be restricted under the
      pooling-of-interests accounting rules. Pursuant to the merger agreement,
      these persons have signed agreements acknowledging these restrictions.

Q:    WHAT HAPPENS IF I CHOOSE NOT TO SUBMIT A PROXY OR TO VOTE?

A:    If a Basin stockholder does not submit a proxy or vote at the Basin
      special stockholder meeting, it will have the same effect as a vote
      against adoption and approval of the merger agreement and approval of the
      merger. If a Stone stockholder does not submit a proxy or vote at the
      Stone special stockholder meeting, it will have the same effect as a vote
      against the amendment to Stone's certificate of incorporation and the
      issuance of shares of Stone common stock in connection with the merger.

Q:    WHAT ARE THE TAX CONSEQUENCES OF THE MERGER TO ME?

A:    Basin and Stone each expect the merger to qualify as a tax-free
      reorganization for U.S. federal income tax purposes. If you are a Basin
      stockholder, your exchange of shares of Basin common stock for shares of
      Stone common stock generally will not cause you to recognize any taxable
      gain or loss. A Basin stockholder will, however, recognize taxable gain or
      loss on any cash received in lieu of a fractional share of Stone common
      stock. Please review carefully the information under the caption "U.S.
      Federal Income Tax Consequences of the Merger" beginning on page 52 for a
      description of the material U.S. federal income tax consequences of the
      merger. The tax consequences to you will depend on your own situation.
      Please consult your tax advisors for a full understanding of the tax
      consequences of the merger to you.

Q:    AM I ENTITLED TO APPRAISAL RIGHTS?

A:    No. Neither holders of Basin common stock nor holders of Stone common
      stock are entitled to appraisal rights in connection with the merger.

                                        3
<PAGE>   12

Q:    WILL THE RIGHTS OF A BASIN STOCKHOLDER CHANGE AS A RESULT OF THE
      MERGER?

A:    Yes. While both Basin and Stone are Delaware corporations and are governed
      by Delaware law, Stone stockholder rights are governed by Stone's
      certificate of incorporation and by-laws, while Basin stockholder rights
      are governed by Basin's certificate of incorporation and by-laws. Basin
      stockholders will become Stone stockholders as a result of the merger and,
      accordingly, their rights will instead be governed by Stone's certificate
      of incorporation and by-laws.

Q:    IF I HAVE MORE QUESTIONS ABOUT THE MERGER OR THE TWO COMPANIES,
      WHERE CAN I FIND ANSWERS?

A:    In addition to reading this document, its annexes and the documents we
      have incorporated in this document by reference, you can find more
      information about the merger or about the two companies in our companies'
      filings with the SEC and, in the case of Stone, with the NYSE, and, in the
      case of Basin, with the Nasdaq National Market.

                                        4
<PAGE>   13

                                    SUMMARY

     This summary highlights selected information from this joint proxy
statement/prospectus and may not contain all of the information that is
important to you. You should carefully read this entire document and the other
documents to which this document refers to fully understand the merger and the
other matters being submitted to stockholders. See "Where You Can Find More
Information" on page 88. Each item in this summary includes a page reference
directing you to a more complete description of that item.

THE COMPANIES (PAGE 69)

    BASIN EXPLORATION, INC.
    1670 Broadway, Suite 2800
    Denver, Colorado 80202
    (303) 685-8000

     Basin is an independent oil and gas exploration and production company with
principal reserves and producing properties located in the shallow waters of the
Gulf of Mexico and selected areas of the onshore United States, including the
Powder River and Green River Basins of Wyoming. As of December 31, 1999, Basin
had estimated proved reserves of approximately 134.1 Bcf of natural gas and 12.6
MMBbls of oil, or an aggregate of approximately 210 Bcfe, 71% of which was
classified as proved developed.

    STONE ENERGY CORPORATION
    625 East Kaliste Saloom Road
    Lafayette, Louisiana 70508
    (337) 237-0410

     Stone is an independent oil and gas exploration and production company with
reserves and producing properties located onshore and in shallow waters offshore
Louisiana. As of December 31, 1999, Stone had estimated proved reserves of
approximately 251.6 Bcf of natural gas and 22.6 MMBbls of oil, or an aggregate
of approximately 387.4 Bcfe, 80% of which was classified as proved developed.

    PARTNER ACQUISITION CORP.
    625 East Kaliste Saloom Road
    Lafayette, Louisiana 70508
    (337) 237-0410

     Partner Acquisition Corp. is a wholly-owned subsidiary of Stone recently
formed for the purpose of effecting the merger.

THE SPECIAL MEETINGS (PAGE 22)

  Basin Stockholders

     The Basin special meeting of stockholders will be held on             ,
2000, at   a.m., local time, at      . At the Basin special meeting, Basin
stockholders will be asked to approve the merger agreement and the transactions
contemplated by the merger agreement, including the merger.

  Stone Stockholders

     The Stone special meeting of stockholders will be held on             ,
2000, at   a.m., local time, at      . At the Stone special meeting, Stone
stockholders will be asked to approve an amendment to Stone's certificate of
incorporation to increase the authorized shares of Stone's common stock from
25,000,000 shares to             shares and the issuance of shares of Stone
common stock to Basin stockholders in connection with the merger. Approval of
the proposal to amend Stone's certificate of incorporation is a prerequisite to
approval of the proposal for the share issuance.

                                        5
<PAGE>   14

RECORD DATE; VOTE REQUIRED (PAGES 22-24)

  Basin Stockholders

     You can vote at the Basin special meeting if you owned shares of Basin
common stock at the close of business on           , 2000. On that date, there
were     shares of Basin common stock outstanding and entitled to vote. You can
cast one vote for each share of Basin common stock you then owned. Approval of
the merger agreement and the transactions contemplated by the merger agreement,
including the merger, requires the approval of the holders of a majority of the
outstanding shares of Basin common stock. Basin directors collectively own
shares of Basin common stock, representing approximately   % of the shares of
Basin common stock outstanding as of the record date. These persons, solely in
their capacity as stockholders of Basin, are parties to the Basin voting
agreement pursuant to which they have agreed to vote their shares of Basin
common stock in favor of the merger. As of             , 2000, Basin executive
officers (other than those officers who are also directors) beneficially owned
approximately   % of the outstanding shares of Basin common stock. These
individuals have indicated that they intend to vote their shares of Basin common
stock in favor of the merger proposal.

  Stone Stockholders

     You can vote at the Stone special meeting if you owned shares of Stone
common stock at the close of business on           , 2000. On that date, there
were     shares of Stone common stock outstanding and entitled to vote. You can
cast one vote for each Stone common share you then owned. Approval of the
amendment to Stone's certificate of incorporation to increase the authorized
shares of Stone's common stock requires the approval of the holders of a
majority of all outstanding shares of Stone common stock. Approval of the share
issuance requires the approval of the holders of a majority of the votes cast on
the proposal, provided that the total votes cast on the proposal represent over
50% in interest of all shares of Stone common stock. Approval of the proposal to
amend Stone's certificate of incorporation is a prerequisite to approval of the
proposal for the share issuance. Stone directors collectively own     shares of
Stone common stock, representing approximately   % of the shares of Stone common
stock outstanding as of the record date. These persons, solely in their capacity
as stockholders of Stone, are parties to the Stone voting agreement pursuant to
which they have agreed to vote their shares of Stone common stock in favor of
the amendment to Stone's certificate of incorporation and the share issuance. As
of           , 2000, Stone executive officers (other than those officers who are
also directors) beneficially owned approximately   % of the outstanding shares
of Stone common stock. These individuals have indicated that they intend to vote
their shares of Stone common stock in favor of the Stone proposals.

THE MERGER AGREEMENT (PAGE 54)

     The merger agreement is attached as Annex A to this document. Although the
merger agreement is the legal document that governs the merger, we also urge you
to carefully consider all of the information in this joint proxy
statement/prospectus in making your decision as to how you will vote on the
merger.

  General

     We propose a merger transaction in which Partner Acquisition Corp., a
wholly-owned subsidiary of Stone created for the purpose of effecting the
merger, will merge with and into Basin Exploration, Inc. After the merger, Basin
will be a wholly-owned subsidiary of Stone and Basin stockholders will become
Stone stockholders.

  Exchange of Common Shares (page 54)

     When we complete the merger, shares of Basin common stock will be converted
into shares of Stone common stock.

                                        6
<PAGE>   15

  Basin Stockholders

     Each share of Basin common stock held prior to the effective time of the
merger will be converted into the right to receive .3974 of a share of Stone
common stock.

     Each assumed Basin option will be converted into an option to acquire, on
the same terms and conditions in effect for the option immediately prior to the
closing date of the merger, that number of shares of Stone common stock
determined by multiplying the number of shares of Basin common stock subject to
that option immediately prior to the closing date of the merger by .3974 and
rounding out to the next whole number of shares. The exercise price per share of
Stone common stock subject to each assumed option will be equal to the amount
determined by dividing the exercise price per share of Basin common stock in
effect for that option immediately prior to the closing date of the merger by
 .3974 and rounding up to the nearest whole cent.

     Former Basin stockholders will own approximately 29% of the shares of Stone
common stock outstanding after the merger.

  Stone Stockholders

     Each share of Stone common stock will remain issued and outstanding as one
share of Stone common stock. Current Stone stockholders will own approximately
71% of the shares of Stone common stock outstanding after the merger.

  Management and Operations after the Merger (page 54)

     After the merger, the Stone management and board of directors will continue
to manage the business of Stone, which will include the business of Basin as a
wholly-owned subsidiary. The combined company will be called "Stone Energy
Corporation" and will be headquartered in Lafayette, Louisiana.

     Stone has agreed to appoint Michael S. Smith, currently the Chairman of the
Board, President and Chief Executive Officer of Basin, to Stone's board of
directors.

  Our Recommendations to Stockholders (pages 29-32)

     Basin Stockholders.  The members of the Basin board of directors
unanimously approved the merger and unanimously recommend that you vote FOR the
proposal to approve the merger agreement and the transactions contemplated by
the merger agreement, including the merger.

     Stone Stockholders.  The members of the Stone board of directors
participating in the board decision on the transaction unanimously recommend
that Stone stockholders vote at the special meeting to approve the amendment to
Stone's certificate of incorporation to increase the authorized shares of
Stone's common stock from 25,000,000 shares to             shares and the
issuance of Stone common stock in connection with the merger. One of Stone's
directors did not participate in the board decision on the transaction due to an
affiliation with Basin's financial advisor in this transaction.

  Opinion of Basin's Financial Advisor (page 33)

     On October 28, 2000, Goldman, Sachs & Co., Basin's financial advisor,
rendered an oral opinion, subsequently confirmed in writing, to the Basin board
of directors as to the fairness, from a financial point of view, as of that
date, to the holders of Basin common stock of the exchange ratio of .3974 of a
share of Stone common stock for each share of Basin common stock. We have
attached this opinion as Annex B to this document. You should read this opinion
in its entirety to understand the procedures followed, assumptions made, matters
considered and limits of the scope of the review undertaken.

     Goldman Sachs provided its opinion for the information and assistance of
Basin's board of directors in connection with its consideration of the merger.
The Goldman Sachs opinion is not a recommendation to any Basin stockholder as to
how that stockholder should vote at the special meeting.

                                        7
<PAGE>   16

  Opinion of Stone's Financial Advisor (page 37)

     On October 28, 2000, Merrill Lynch & Co., Stone's financial advisor,
rendered its oral opinion, subsequently confirmed in writing, to the Stone board
of directors as to the fairness, from a financial point of view, as of that
date, to Stone of the exchange ratio of .3974 of a share of Stone common stock
for each share of Basin common stock. We have attached this opinion as Annex C
to this document. You should read this opinion in its entirety to understand the
procedures followed, assumptions made, matters considered and limits of the
scope of the review undertaken.

     Merrill Lynch's opinion is addressed to the Stone board of directors and
does not constitute a recommendation to any Stone stockholder as to how that
stockholder should vote at the special meeting.

  Conditions to Completion of the Merger (page 64)

     The completion of the merger depends on a number of conditions being
satisfied or waived. In addition to customary conditions relating to the
accuracy of representations and warranties and our compliance with the merger
agreement, these conditions include the following:

     - the merger agreement and the merger have been approved and adopted by
       Basin's stockholders and the amendment to Stone's certificate of
       incorporation to authorize additional shares of Stone common stock and
       the issuance of Stone common stock in the merger have been approved by
       Stone's stockholders;

     - the SEC has declared the registration statement effective under the
       Securities Act, and the registration statement is not subject to any stop
       order or proceedings seeking a stop order;

     - the shares of Stone common stock to be issued in the merger have been
       approved for listing on the New York Stock Exchange;

     - any applicable waiting period under the Hart-Scott-Rodino Antitrust
       Improvements Act relating to the merger has expired or been terminated;

     - all authorizations, consents, orders or approvals of, or declarations or
       filings with, or expirations of waiting periods imposed by, any
       governmental authority have been filed, obtained or occurred, except in
       those cases where no material adverse effect would result;

     - no governmental entity or federal, state or foreign court of competent
       jurisdiction has enacted, issued, promulgated, enforced or entered any
       order or statute, rule or regulation that is in effect and that has the
       effect of making the merger illegal or otherwise prohibiting the
       consummation of the merger;

     - Stone and Basin each has received an opinion of tax counsel to the effect
       that the merger will be treated for federal income tax purposes as a
       tax-free reorganization within the meaning of Section 368(a) of the
       Internal Revenue Code; and

     - except as otherwise provided by the merger agreement, Stone and Basin
       each has received a letter from Arthur Andersen LLP, independent public
       accountants to both Stone and Basin, confirming that the merger, for
       financial accounting purposes, is a pooling of interests.

  Termination of the Agreement (page 65)

     We can agree at any time to terminate the merger agreement without
completing the merger, even if Basin stockholders have approved the merger and
Stone stockholders have approved the amendment to Stone's certificate of
incorporation to increase the authorized shares of Stone's common stock and the
issuance of Stone common stock in connection with the merger. Also, the merger
agreement can be terminated in the following circumstances:

     - by either of us if the merger has not been completed by May 31, 2001,
       except that the right to terminate the merger agreement under this
       provision is not available to any party whose failure to

                                        8
<PAGE>   17

fulfill any of its obligations under the merger agreement was the cause of or
resulted in the failure of the merger to occur on or before May 31, 2001;

     - by either of us if a court of competent jurisdiction or other
       governmental entity has issued a non-appealable final order, decree or
       ruling or taken any other non-appealable final action, in each case
       having the effect of permanently enjoining or otherwise permanently
       prohibiting the merger;

     - by either of us if, at Basin's stockholders' meeting, Basin does not
       obtain the requisite vote of its stockholders in favor of the merger, or
       if, at Stone's stockholders' meeting, the required vote for the amendment
       to Stone's certificate of incorporation and the approval of the issuance
       of Stone common stock in the merger is not obtained;

     - by Stone, if (1) Basin's board of directors has withdrawn or modified, in
       a manner adverse to Stone, its recommendation of the merger agreement or
       the merger, (2) Basin's board of directors has recommended to Basin's
       stockholders an acquisition proposal that is more favorable than Stone's
       acquisition proposal, or (3) a tender offer or exchange offer for more
       than 35% of the outstanding shares of Basin's capital stock is commenced
       and Basin's board of directors recommends in favor of the acceptance of
       such offer;

     - by Basin, if Stone's board of directors has withdrawn or modified, in a
       manner adverse to Basin, its recommendation of the amendment to Stone's
       certificate of incorporation and the issuance of Stone common stock in
       the merger; or

     - by either of us if, there has been a breach of any representation,
       warranty, covenant or agreement on the part of the other party set forth
       in the merger agreement, which breach (1) would, if uncured at closing,
       cause the closing conditions relating to our respective representations
       and warranties and performance of our respective obligations not to be
       satisfied, and (2) the breach is not cured within 20 business days after
       written notice of the breach is received from the other party.

  Termination Fees (page 66)

     Stone must pay Basin a fee of $15 million in cash if the merger agreement
is terminated in a number of circumstances described elsewhere in this document.
Please see page 66.

     Similarly, Basin must pay Stone a fee of $15 million in cash if the merger
agreement is terminated in a number of circumstances described elsewhere in this
document. Please see page 67.

  Accounting Treatment (page 50)

     The merger will be accounted for as a pooling of interests for accounting
and financial reporting purposes. Under this method of accounting, the recorded
assets and liabilities of Stone and Basin will be carried forward to the
combined company at their recorded amounts, and income of the combined company
will include income of Stone and Basin for the entire fiscal year in which the
merger occurs as well as for prior periods.

VOTING AGREEMENTS (PAGE 68)

  Basin Voting Agreement

     In connection with the execution and delivery of the merger agreement,
Stone entered into the Basin voting agreement with the existing directors of
Basin, solely in their capacity as stockholders, under which these stockholders
agreed to vote their shares of Basin common stock in favor of the adoption of
the merger agreement. As of the record date for the special meeting, these
stockholders owned shares of Basin common stock representing approximately   %
of the total voting power of the outstanding Basin common stock. Approval of the
merger agreement and the transactions contemplated by the merger agreement,
including the merger, requires the approval of the holders of a majority of the
outstanding shares of Basin common stock.

                                        9
<PAGE>   18

     These Basin stockholders also agreed not to solicit, initiate or encourage
the submission of any proposal or offer for a merger, consolidation, business
combination, share exchange, recapitalization, sale of all or substantially all
of Basin's assets or similar transactions involving Basin or any of its
subsidiaries or participate in any negotiations regarding, or furnish to any
person any information with respect to, or take any other action to facilitate
any inquiries or the making of any proposal that constitutes or may reasonably
be expected to lead to any of the above, or agree to or recommend any of the
above, except as would be permitted by Basin under the merger agreement. The
Basin voting agreement prohibits, subject to limited exceptions, any stockholder
from selling, transferring, pledging, assigning or otherwise disposing of any
shares of Basin common stock. The Basin voting agreement terminates upon the
earlier to occur of the completion of the merger and the termination of the
merger agreement in accordance with its terms.

     The Basin voting agreement is attached as an exhibit to Annex A to this
joint proxy statement/ prospectus. We urge you to read the full text of the
Basin voting agreement.

  Stone Voting Agreement

     In connection with the execution and delivery of the merger agreement,
Basin entered into the Stone voting agreement with the existing directors of
Stone, solely in their capacity as stockholders, under which these stockholders
agreed to vote their shares of Stone common stock in favor of the amendment to
Stone's certificate of incorporation to increase the authorized shares of Stone
common stock and the issuance of shares of Stone common stock in connection with
the merger. As of the record date for the special meeting, these stockholders
owned shares of Stone common stock representing approximately   % of the total
voting power of the outstanding Stone common stock. Approval of the amendment to
Stone's certificate of incorporation to increase the authorized shares of
Stone's common stock requires the approval of the holders of a majority of all
outstanding shares of Stone common stock. Approval of the share issuance
requires the approval of the holders of a majority of the votes cast on the
proposal, provided that the total votes cast on the proposal represent over 50%
in interest of all outstanding shares of Stone common stock. Approval of the
proposal to amend Stone's certificate of incorporation is a prerequisite to
approval of the proposal for the share issuance.

     These Stone stockholders agreed not to solicit, initiate or encourage the
submission of any takeover proposal for Stone or participate in any discussions
or negotiations regarding, or furnish to any person any information with respect
to, or take any other action to facilitate any inquiries or the making of any
proposal that constitutes or may reasonably be expected to lead to any takeover
proposal for Stone. The Stone voting agreement prohibits, subject to limited
exceptions, any stockholder from selling, transferring, pledging, encumbering,
assigning or otherwise disposing of any shares of Stone common stock. The Stone
voting agreement terminates upon the earlier to occur of the completion of the
merger and the termination of the merger agreement in accordance with its terms.

     The Stone voting agreement is attached as an exhibit to Annex A to this
joint proxy statement/ prospectus. We urge you to read the full text of the
Stone voting agreement.

INTERESTS OF CERTAIN PEOPLE IN THE MERGER THAT ARE DIFFERENT FROM YOUR INTERESTS
(PAGE 46)

  Basin

     In considering the recommendation of the Basin board of directors with
respect to the merger, you should be aware that some executive officers and
directors of Basin have interests in the merger that are in addition to your
interests as a shareholder of Basin generally. The Basin board of directors was
aware of the potential conflicts described below and considered them in
approving the merger.

     Pursuant to their employment or other change-in-control type agreements,
the following Basin officers are entitled to receive various benefits, such as
bonuses, severance payments and vesting of stock options and performance shares,
because the merger will constitute a "change of control" for purposes of such
agreements:

     - Michael S. Smith, President, Chief Executive Officer and Director;

                                       10
<PAGE>   19

     - Neil L. Stenbuck, Vice President, Chief Financial Officer and Director;

     - Howard L. Boigon, Vice President, General Counsel and Director;

     - Thomas J. Corley, Vice President, Engineering and Production;

     - Patrick A. Jackson, Vice President, Onshore Exploration;

     - Dalton F. Polasek, Vice President, Gulf Coast Engineering;

     - David A. Pustka, Vice President, Gulf Coast Exploration; and

     - Samuel D. Winegrad, Vice President, Corporate Development.

     Additionally, Mr. Smith, the current chief executive officer of Basin, has
agreed to enter into a confidentiality and non-compete agreement with Stone in
connection with the merger. In exchange for Mr. Smith's confidentiality and
non-compete agreement Stone will pay Mr. Smith $300,000 per year for each of the
next three (3) years following completion of the merger.

  Stone

     One of Stone's directors, Peter K. Barker, is an advisory director of
Goldman Sachs, Basin's financial advisor. Mr. Barker did not participate in the
board decision on this transaction.

     Additional information on the interests of Basin directors and executive
officers is described elsewhere in this document. Please see pages 46 through
49.

     Our boards of directors knew about these interests, and considered them, in
approving the merger and recommending that our stockholders approve the merger
transaction.

APPRAISAL RIGHTS (PAGE 51)

     Under Delaware law, Basin common stockholders are not entitled to appraisal
rights in connection with the merger.

CERTAIN FEDERAL INCOME TAX CONSEQUENCES (PAGE 52)

  Basin Stockholders

     We expect that, for U.S. federal income tax purposes, the merger will be
classified as a reorganization within the meaning of Section 368(a) of the
Internal Revenue code. Assuming that the merger meets this classification, the
exchange of shares of Basin common stock for shares of Stone common stock
generally will not cause a Basin stockholder to recognize any taxable gain or
loss. Basin stockholders will, however, recognize taxable gain or loss in
connection with any cash received instead of fractional shares.

     BASIN STOCKHOLDERS ARE STRONGLY URGED TO CONSULT THEIR TAX ADVISORS AS TO
THE SPECIFIC TAX CONSEQUENCES TO THEM OF THE MERGER, INCLUDING THE APPLICABILITY
AND EFFECT OF U.S. FEDERAL, STATE AND LOCAL AND FOREIGN INCOME AND OTHER TAX
LAWS IN THEIR PARTICULAR CIRCUMSTANCES.  It is a condition to the merger that
Basin and Stone each receive an opinion from tax counsel to the effect that the
merger will qualify as a reorganization within the meaning of Section 368(a) of
the Internal Revenue Code. These opinions will be based on customary assumptions
and customary representations made by, among others, Basin, Stone and Partner
Acquisition Corp. An opinion of counsel represents counsel's best legal judgment
and is not binding on the Internal Revenue Service or any court. No ruling has
been, or will be, sought from the Internal Revenue Service as to the U.S.
federal income tax consequences of the merger.

  Stone Stockholders

     Because shares of Stone common stock will remain unchanged, the merger
should not cause a Stone stockholder to recognize any taxable gain or loss for
U.S. federal income tax purposes.

                                       11
<PAGE>   20

     THIS TAX TREATMENT MAY NOT APPLY TO CERTAIN STOCKHOLDERS. DETERMINING THE
ACTUAL TAX CONSEQUENCES OF THE MERGER TO YOU MAY BE COMPLICATED. THESE
CONSEQUENCES WILL DEPEND ON YOUR SPECIFIC SITUATION AND ON VARIABLES NOT WITHIN
OUR CONTROL. YOU SHOULD CONSULT YOUR OWN TAX ADVISOR FOR A FULL UNDERSTANDING OF
THE MERGER'S TAX CONSEQUENCES FOR YOU.

CERTAIN DIFFERENCES IN THE RIGHTS OF STOCKHOLDERS (PAGE 80)

     As a result of the merger, the stockholders of Basin will become
stockholders of Stone. As stockholders of Stone, their rights will continue to
be governed by the Delaware General Corporation Law, but their rights will also
be governed by Stone's certificate of incorporation and by-laws. See pages 79
through 84 for summaries of certain material differences between the rights of
Stone stockholders and Basin stockholders.

REGULATORY APPROVALS (PAGE 50)

     Under the Hart-Scott-Rodino Act, we may not complete the merger unless we
make various filings with the Antitrust Division of the U.S. Department of
Justice and the U.S. Federal Trade Commission and certain waiting periods expire
or are terminated. On             , 2000, Stone and Basin submitted the required
filings to the Federal Trade Commission and the Antitrust Division. The waiting
period under the Hart-Scott-Rodino Act terminated on             , 2000.

COMPARATIVE PER SHARE MARKET PRICE INFORMATION

     Shares of Stone common stock are listed on the New York Stock Exchange and
Basin common stock is quoted on the Nasdaq National Market. On October 27, 2000,
the last trading day before we announced the merger, shares of Stone common
stock closed at $54.16 per share and shares of Basin common stock closed at
$19.56 per share. On             , 2000, the most recent practicable date before
the mailing of this document, shares of Stone common stock closed at $     per
share and shares of Basin common stock closed at $     per share.

     Based on the exchange ratio in the merger, which is .3974 of a share of
Stone common stock per share of Basin common stock, the market value of the
consideration that Basin common stockholders will receive in the merger for
shares of Basin common stock would be $     per share based on the closing price
of shares of Stone common stock on             , 2000, and $     per share based
on the closing price of shares of Stone common stock on             , 2000. Of
course, the market price of shares of Stone common stock will fluctuate prior to
and after the merger, whereas the exchange ratio is fixed. You should obtain
current stock price quotations for Stone common stock and shares of Basin common
stock.

                                       12
<PAGE>   21

           SELECTED HISTORICAL FINANCIAL AND OPERATING DATA OF STONE

     The following table sets forth selected historical financial and operating
data of Stone as of and for the nine months ended September 30, 2000 and 1999
and for each of the years in the five-year period ended December 31, 1999. You
should read this data along with the historical financial statements and related
notes of Stone incorporated herein by reference.

<TABLE>
<CAPTION>
                                                  NINE MONTHS ENDED
                                                    SEPTEMBER 30,
                                                     (UNAUDITED)                       YEAR ENDED DECEMBER 31,
                                                 --------------------   ------------------------------------------------------
                                                   2000        1999       1999       1998        1997        1996       1995
                                                 ---------   --------   --------   ---------   ---------   --------   --------
                                                         (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AND PER UNIT AMOUNTS)
<S>                                              <C>         <C>        <C>        <C>         <C>         <C>        <C>
STATEMENT OF OPERATIONS DATA:
Revenues:
  Production revenues..........................  $ 177,839   $106,858   $146,919   $ 114,597   $  69,079   $ 55,839   $ 38,693
  Other revenue................................      2,705      1,361      2,215       2,023       1,908      2,126      1,858
                                                 ---------   --------   --------   ---------   ---------   --------   --------
        Total revenues.........................    180,544    108,219    149,134     116,620      70,987     57,965     40,551
                                                 ---------   --------   --------   ---------   ---------   --------   --------
Expenses:
  Direct operating expenses(1).................     28,910     18,812     25,759      21,403      14,182     12,451      9,797
  Depreciation, depletion and amortization.....     56,528     50,708     65,803      68,187      28,739     19,564     15,719
  Write-down of oil and gas properties.........         --         --         --      89,135          --         --         --
  Interest expense.............................      6,263     10,677     12,840      12,950       4,916      3,574      2,191
  General and administrative expenses..........      5,357      4,335      6,181       5,056       4,736      4,437      3,383
                                                 ---------   --------   --------   ---------   ---------   --------   --------
        Total expenses.........................     97,058     84,532    110,583     196,731      52,573     40,026     31,090
                                                 ---------   --------   --------   ---------   ---------   --------   --------
Net income (loss) before income taxes..........     83,486     23,687     38,551     (80,111)     18,414     17,939      9,461
                                                 ---------   --------   --------   ---------   ---------   --------   --------
Income tax provision (benefit):
    Current....................................        272          5         25          --          --        208        131
    Deferred...................................     28,948      8,303     12,036     (28,480)      6,495      6,698      3,514
                                                 ---------   --------   --------   ---------   ---------   --------   --------
        Total income taxes.....................     29,220      8,308     12,061     (28,480)      6,495      6,906      3,645
                                                 ---------   --------   --------   ---------   ---------   --------   --------
Net income (loss)..............................  $  54,266   $ 15,379   $ 26,490   $ (51,631)  $  11,919   $ 11,033   $  5,816
                                                 =========   ========   ========   =========   =========   ========   ========
Earnings (loss) per share:
  Basic earnings (loss) per share..............  $    2.95   $   0.97   $   1.61   $   (3.43)  $    0.79   $   0.90   $   0.49
                                                 =========   ========   ========   =========   =========   ========   ========
  Diluted earnings (loss) per share............  $    2.89   $   0.95   $   1.58   $   (3.43)  $    0.78   $   0.90   $   0.49
                                                 =========   ========   ========   =========   =========   ========   ========
CASH FLOW DATA:
  Cash provided by operating activities........  $ 157,618   $ 66,601   $ 78,850   $  85,633   $  32,679   $ 32,751   $ 27,650
  Cash used in investing activities............   (109,454)   (76,735)   (97,799)   (163,471)   (135,080)   (73,661)   (51,507)
  Cash provided by financing activities........      2,341     22,095     22,273      78,084     102,841     44,488     25,013
BALANCE SHEET DATA (AT END OF PERIOD):
  Working capital..............................  $  40,032   $ 27,468   $ 22,887   $   9,884   $   8,328   $  6,683   $  5,379
  Oil and gas properties, net..................    415,125    339,419    353,141     293,824     291,420    171,396    111,248
  Total assets.................................    544,982    423,215    441,738     366,390     354,144    209,406    139,460
  Long-term debt, less current portion.........    100,000    100,000    100,000     209,936     132,024     26,172     47,754
  Stockholders' equity.........................    324,865    252,830    265,587     105,332     156,637    144,441     66,927
PRODUCTION:
  Oil (MBbls)..................................      2,494      2,631      3,469       2,876       1,585      1,356      1,400
  Gas (MMcf)(2)................................     34,353     29,130     38,113      33,281      14,183     11,331      8,399
  Oil and gas (MMcfe)(2).......................     49,317     44,916     58,927      50,537      23,693     19,467     16,799
AVERAGE SALES PRICES:(3)
  Oil (per Bbl)................................  $   25.12   $  14.97   $  16.42   $   13.40   $   19.61   $  20.49   $  17.70
  Gas (per Mcf)(2).............................       3.35       2.32       2.36        2.29        2.68       2.48       1.66
  Oil and gas (per Mcfe)(2)....................       3.61       2.38       2.49        2.27        2.92       2.87       2.30
AVERAGE COSTS (PER MCFE):
  Direct operating expenses(1).................  $    0.59   $   0.42   $   0.44   $    0.42   $    0.60   $   0.64   $   0.58
  General and administrative(4)................       0.09       0.07       0.08        0.08        0.16       0.18       0.20
  DD&A.........................................       1.15       1.13       1.12        1.35        1.21       1.00       0.94
PROVED RESERVES AT DECEMBER 31:
  Oil (MBbls)..................................                           22,636      18,476      17,763     12,772      7,985
  Gas (MMcf)...................................                          251,614     243,270     189,239    144,316     81,179
  Oil and gas (MMcfe)..........................                          387,430     354,126     295,817    220,948    129,089
Present value of estimated future net cash
  flows before income taxes....................                         $561,303   $ 286,098   $ 368,930   $443,793   $179,725
</TABLE>

---------------
(1) Includes normal lease operating expenses, major maintenance expenses and
    production taxes.
(2) Results from July 1, 1999 forward include net daily production of 7.3 MMcf
    at $2.24 per Mcf associated with the amortization of a volumetric production
    payment.
(3) Includes the effects of hedging activities.
(4) Excludes incentive compensation expense.

                                       13
<PAGE>   22

           SELECTED HISTORICAL FINANCIAL AND OPERATING DATA OF BASIN

     The following table sets forth selected historical financial and operating
data of Basin as of and for the nine months ended September 30, 2000 and 1999
and for each of the years in the five-year period ended December 31, 1999. You
should read this data along with the historical financial statements and related
notes of Basin incorporated herein by reference.

<TABLE>
<CAPTION>
                                                  NINE MONTHS ENDED
                                                    SEPTEMBER 30,
                                                     (UNAUDITED)                      YEAR ENDED DECEMBER 31,
                                                 -------------------   -----------------------------------------------------
                                                   2000       1999       1999       1998        1997       1996       1995
                                                 --------   --------   --------   ---------   --------   --------   --------
                                                        (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AND PER UNIT AMOUNTS)
<S>                                              <C>        <C>        <C>        <C>         <C>        <C>        <C>
STATEMENT OF OPERATIONS DATA:
Revenues:
  Production revenues..........................  $ 84,007   $ 52,750   $ 71,496   $  48,620   $ 24,401   $ 18,182   $ 39,645
  Other revenue(1).............................       167         83        134          79        319     23,481        831
                                                 --------   --------   --------   ---------   --------   --------   --------
        Total revenues.........................    84,174     52,833     71,630      48,699     24,720     41,663     40,476
                                                 --------   --------   --------   ---------   --------   --------   --------
Expenses:
  Direct operating expenses(2).................    11,448      8,889     11,661       9,046      5,860      6,605     11,674
  Depreciation, depletion and amortization.....    31,869     29,130     39,494      29,775     10,622      7,606     17,202
  Write-down of oil and gas properties.........        --         --         --      38,500         --         --     26,500
  Interest expense.............................       586      2,195      2,279       2,030        764      2,272      6,929
  General and administrative expenses..........     4,932      5,153      6,160       4,380      3,694      3,850      5,498
                                                 --------   --------   --------   ---------   --------   --------   --------
        Total expenses.........................    48,835     45,367     59,594      83,731     20,940     20,333     67,803
                                                 --------   --------   --------   ---------   --------   --------   --------
Net income (loss) before income taxes..........    35,339      7,466     12,036     (35,032)     3,780     21,330    (27,327)
                                                 --------   --------   --------   ---------   --------   --------   --------
Income tax provision (benefit):
  Current......................................        --         --         --          23       (471)     1,000         --
  Deferred.....................................    10,852         --         --      (6,555)     1,795      4,760     (7,784)
                                                 --------   --------   --------   ---------   --------   --------   --------
        Total income taxes.....................    10,852         --         --      (6,532)     1,324      5,760     (7,784)
                                                 --------   --------   --------   ---------   --------   --------   --------
Net income (loss)..............................  $ 24,487   $  7,466   $ 12,036   $ (28,500)  $  2,456   $ 15,570   $(19,543)
                                                 ========   ========   ========   =========   ========   ========   ========
Earnings (loss) per common share:
  Basic earnings (loss) per common share.......  $   1.32   $   0.48   $   0.74   $   (2.06)  $   0.22   $   1.45   $  (1.82)
                                                 ========   ========   ========   =========   ========   ========   ========
  Diluted earnings (loss) per common share.....  $   1.30   $   0.47   $   0.72   $   (2.06)  $   0.22   $   1.45   $  (1.82)
                                                 ========   ========   ========   =========   ========   ========   ========
CASH FLOW DATA:
  Cash provided by operating activities........  $ 67,155   $ 29,020   $ 48,897   $  37,834   $ 15,489   $  4,909   $ 10,320
  Cash provided by (used in) investing
    activities(1)..............................   (79,834)   (44,185)   (65,505)   (107,664)   (98,050)    92,627    (13,841)
  Cash provided by (used in) financing
    activities(1)..............................    13,421     15,368     20,054      69,630     61,069    (77,126)      (260)
BALANCE SHEET DATA (AT END OF PERIOD):
  Working capital (deficit)....................  $ (6,839)  $ (5,640)  $(10,378)  $ (13,224)  $(10,036)  $ 19,178   $ (2,211)
  Oil and gas properties, net(1)...............   264,494    204,001    218,205     186,403    147,089     51,882    130,920
  Total assets(1)..............................   300,171    226,848    248,905     201,163    161,959     84,957    146,651
  Long-term debt, less current portion(1)......    48,000     29,000     34,000      80,000     11,053        218     77,172
  Stockholders' equity.........................   200,123    171,061    175,163      94,219    121,365     68,751     53,287
PRODUCTION:(1)
  Oil (MBbls)..................................       778        624        855         725        524        564      1,153
  Gas (MMcf)...................................    19,338     20,772     27,400      17,616      5,509      4,776     12,833
  Oil and gas (MMcfe)..........................    24,006     24,516     32,530      21,966      8,653      8,160     19,751
AVERAGE SALES PRICES:(3)
  Oil (per Bbl)................................  $  28.37   $  14.67   $  15.26   $   13.42   $  18.80   $  20.03   $  17.02
  Gas (per Mcf)................................      3.20       2.10       2.13        2.21       2.64       1.44       1.56
  Oil and gas (per Mcfe).......................      3.50       2.15       2.20        2.21       2.82       2.23       2.01
AVERAGE COSTS (PER MCFE):
  Direct operating expenses(2).................  $   0.48   $   0.36   $   0.36   $    0.41   $   0.68   $   0.81   $   0.59
  General and administrative(4)................      0.18       0.15       0.15        0.18       0.38       0.46       0.26
  DD&A.........................................      1.33       1.19       1.21        1.36       1.23       0.93       0.87
PROVED RESERVES AT DECEMBER 31:(1)
  Oil (MBbls)..................................                          12,577       8,667      8,154      7,870     12,606
  Gas (MMcf)...................................                         134,053     127,502     89,534     29,713    131,436
  Oil and gas (MMcfe)..........................                         209,515     179,504    138,458     76,933    207,072
Present value of estimated future net cash
  flows before income taxes....................                        $269,303   $ 164,485   $160,230   $ 83,656   $129,068
</TABLE>

---------------
(1) 1996 results include a $22.5 million gain on the sale of producing oil and
    gas properties located in the Denver-Julesburg Basin. A portion of the
    proceeds from the $123.5 million sale was used to pay off all outstanding
    bank debt.

(2) Includes lease operating expenses and production taxes.

(3) Includes the effects of hedging activities.

(4) Excludes stock compensation expense.

                                       14
<PAGE>   23

              SELECTED UNAUDITED PRO FORMA COMBINED FINANCIAL AND
                                 OPERATING DATA

     The following tables set forth selected unaudited pro forma combined
financial and operating data to give effect to the merger between Stone and
Basin based on the pooling of interests method of accounting at the exchange
ratio of .3974 of a share of Stone common stock for each share of Basin common
stock. The unaudited pro forma balance sheet data included in the tables below
are presented as if the merger was effective on September 30, 2000. The
unaudited pro forma statement of operations data included in the tables below
are presented as if the merger was effective as of the beginning of the earliest
period presented. The pro forma amounts in the tables below are presented for
informational purposes. You should not rely on the pro forma amounts as being
indicative of the financial position or the results of operations of the
combined company that would have actually occurred had the merger been effective
during the periods presented or of the future financial position or future
results of operations of the combined company. The unaudited pro forma combined
statements of operations exclude non-recurring charges directly attributable to
the merger (estimated at $24 million), substantially all of which will be
charged to operations in the quarter in which the merger is consummated. The
unaudited pro forma combined balance sheet has been adjusted to reflect the
assumed after-tax impact of such non-recurring charges. You should read this
information in conjunction with the historical consolidated financial statements
and accompanying notes of Stone and Basin incorporated in this document by
reference and the condensed unaudited pro forma combined financial statements
and notes thereto beginning on page 71.

<TABLE>
<CAPTION>
                                                       NINE MONTHS ENDED
                                                         SEPTEMBER 30,              YEAR ENDED DECEMBER 31,
                                                    -----------------------   ------------------------------------
                                                       2000         1999         1999         1998         1997
                                                    ----------   ----------   ----------   ----------   ----------
                                                    (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AND PER UNIT AMOUNTS)
<S>                                                 <C>          <C>          <C>          <C>          <C>
STATEMENT OF OPERATIONS DATA:
Revenues:
  Production revenues.............................  $ 261,846    $ 159,608    $ 218,415    $ 163,217    $  93,480
  Other revenue...................................      2,872        1,444        2,349        2,102        2,227
                                                    ---------    ---------    ---------    ---------    ---------
        Total revenues............................    264,718      161,052      220,764      165,319       95,707
                                                    ---------    ---------    ---------    ---------    ---------
Expenses:
  Direct operating expenses(1)....................     40,358       27,701       37,420       30,449       20,042
  Depreciation, depletion and amortization........     84,387       78,365      102,728       99,052       40,383
  Write-down of oil and gas properties............         --           --           --      114,053           --
  Interest expense................................      6,849       12,872       15,119       14,980        5,680
  General and administrative expenses.............     10,289        9,488       12,341        9,436        8,430
                                                    ---------    ---------    ---------    ---------    ---------
        Total expenses............................    141,883      128,426      167,608      267,970       74,535
                                                    ---------    ---------    ---------    ---------    ---------
Net income (loss) before income taxes.............    122,835       32,626       53,156     (102,651)      21,172
                                                    ---------    ---------    ---------    ---------    ---------
Income tax provision (benefit):
  Current.........................................        272            5           25           23         (471)
  Deferred........................................     42,720       11,414       18,580      (35,951)       7,881
                                                    ---------    ---------    ---------    ---------    ---------
        Total income taxes........................     42,992       11,419       18,605      (35,928)       7,410
                                                    ---------    ---------    ---------    ---------    ---------
Net income (loss).................................  $  79,843    $  21,207    $  34,551    $ (66,723)   $  13,762
                                                    =========    =========    =========    =========    =========
Earnings (loss) per share:
  Basic earnings (loss) per share.................  $    3.10    $    0.96    $    1.51    $   (3.24)   $    0.71
                                                    =========    =========    =========    =========    =========
  Diluted earnings (loss) per share...............  $    3.04    $    0.94    $    1.48    $   (3.24)   $    0.70
                                                    =========    =========    =========    =========    =========
CASH FLOW DATA:
  Cash provided by operating activities...........  $ 224,773    $  95,621    $ 127,747    $ 123,467    $  48,168
  Cash used in investing activities...............   (189,288)    (120,920)    (163,304)    (271,135)    (233,130)
  Cash provided by financing activities...........     15,762       37,463       42,327      147,714      163,910
BALANCE SHEET DATA (AT END OF PERIOD):
  Working capital.................................  $   9,193
  Oil and gas properties, net.....................    698,320
  Total assets....................................    863,854
  Long-term debt, less current portion............    148,000
  Stockholders' equity............................    518,324
</TABLE>

                       (see footnotes on following page)
                                       15
<PAGE>   24

                     SELECTED UNAUDITED PRO FORMA COMBINED
                          FINANCIAL AND OPERATING DATA
                                  (CONTINUED)

<TABLE>
<CAPTION>
                                                       NINE MONTHS ENDED
                                                         SEPTEMBER 30,              YEAR ENDED DECEMBER 31,
                                                    -----------------------   ------------------------------------
                                                       2000         1999         1999         1998         1997
                                                    ----------   ----------   ----------   ----------   ----------
                                                    (DOLLARS IN THOUSANDS, EXCEPT PER SHARE AND PER UNIT AMOUNTS)
<S>                                                 <C>          <C>          <C>          <C>          <C>
PRODUCTION:
  Oil (MBbls).....................................      3,272        3,255        4,324        3,601        2,109
  Gas (MMcf)(2)...................................     53,691       49,902       65,513       50,897       19,692
  Oil and gas (MMcfe)(2)..........................     73,323       69,432       91,457       72,503       32,346
AVERAGE SALES PRICES:(3)
  Oil (per Bbl)...................................  $   25.89    $   14.91    $   16.19    $   13.40    $   19.41
  Gas (per Mcf)(2)................................       3.30         2.23         2.27         2.26         2.67
  Oil and gas (per Mcfe)(2).......................       3.57         2.30         2.39         2.25         2.89
AVERAGE COSTS (PER MCFE):
  Direct operating expenses(1)....................  $    0.55    $    0.40    $    0.41    $    0.42    $    0.62
  General and administrative(4)...................       0.12         0.10         0.10         0.11         0.22
  DD&A............................................       1.15         1.13         1.12         1.37         1.25
PROVED RESERVES AT DECEMBER 31:
  Oil (MBbls).....................................                               35,213       27,143       25,917
  Gas (MMcf)......................................                              385,667      370,772      278,773
  Oil and gas (MMcfe).............................                              596,945      533,630      434,275
Present value of estimated future net cash flows
  before income taxes.............................                            $ 830,606    $ 450,583    $ 529,160
</TABLE>

---------------
(1) Includes normal lease operating expenses, major maintenance expenses and
    production taxes.
(2) Results from July 1, 1999 forward include net daily production of 7.3 MMcf
    at $2.24 per Mcf associated with the amortization of a volumetric production
    payment.
(3) Includes the effects of hedging activities.
(4) Excludes incentive and stock compensation expenses.

                       (see footnotes on following page)
                                       16
<PAGE>   25

                           COMPARATIVE PER SHARE DATA

     The following table sets forth certain historical per share data for Stone
and Basin and unaudited pro forma combined and unaudited equivalent pro forma
per share data after giving effect to the proposed merger under the pooling of
interests method of accounting at the exchange ratio of .3974 of a share of
Stone common stock for each share of Basin common stock. You should read this
data in conjunction with the selected historical financial and operating data
and the unaudited pro forma combined financial statements included in this
document, as well as the separate historical consolidated financial statements
of Stone and Basin and the notes thereto incorporated by reference in this
document. The pro forma combined per share data in the table below are presented
for informational purposes. You should not rely on the pro forma amounts as
being indicative of the financial position or the results of operations of the
combined company that would have actually occurred had the merger been effective
during the periods presented or of the future financial position or future
results of operations of the combined company.

<TABLE>
<CAPTION>
                                                     NINE MONTHS
                                                        ENDED
                                                    SEPTEMBER 30,
                                                     (UNAUDITED)      YEAR ENDED DECEMBER 31,
                                                   ---------------    ------------------------
                                                    2000     1999     1999      1998     1997
                                                   ------    -----    -----    ------    -----
<S>                                                <C>       <C>      <C>      <C>       <C>
PRO FORMA COMBINED:
  Earnings (loss) per share -- Basic(1)..........  $ 3.10    $0.96    $1.51    $(3.24)   $0.71
  Earnings (loss) per share -- Diluted(1)........    3.04     0.94     1.48     (3.24)    0.70
  Book value per share...........................   20.04
BASIN EQUIVALENT PRO FORMA:(2)
  Earnings (loss) per share -- Basic.............  $ 1.23    $0.38    $0.60    $(1.29)   $0.28
  Earnings (loss) per share -- Diluted...........    1.21     0.37     0.59     (1.29)    0.28
  Book value per share...........................    7.96
BASIN HISTORICAL:
  Earnings (loss) per share -- Basic.............  $ 1.32    $0.48    $0.74    $(2.06)   $0.22
  Earnings (loss) per share -- Diluted...........    1.30     0.47     0.72     (2.06)    0.22
  Book value per share(3)........................   10.81
STONE HISTORICAL:
  Earnings (loss) per share -- Basic.............  $ 2.95    $0.97    $1.61    $(3.43)   $0.79
  Earnings (loss) per share -- Diluted...........    2.89     0.95     1.58     (3.43)    0.78
  Book value per share(3)........................   17.55
</TABLE>

---------------

(1) Amounts are based upon the weighted average number of common and common
    stock equivalent shares outstanding of Stone and Basin for each period at
    the exchange ratio of .3974 of a share of Stone common stock for each share
    of Basin common stock.

(2) The unaudited equivalent pro forma per share data is calculated by
    multiplying the pro forma combined per share data by the exchange ratio of
    .3974 of a share of Stone common stock for each share of Basin common stock.

(3) Historical book value per share is computed by dividing stockholders' equity
    by the number of shares of common stock outstanding at the end of the
    period.

                                       17
<PAGE>   26

                   PRO FORMA OIL AND GAS RESERVES (UNAUDITED)

     The following table sets forth summary information with respect to
estimates of proved oil and gas reserves and the estimated discounted future net
cash flows before income taxes for these reserves as of December 31, 1999 for
Stone, Basin and for Stone on a pro forma combined basis. For additional
information relating to reserves, see "Risk Factors" in this document and in our
SEC filings incorporated by reference into this document. See "Where You Can
Find More Information."

<TABLE>
<CAPTION>
                                                                           PRO FORMA
                                                      STONE      BASIN     COMBINED
                                                     --------   --------   ---------
                                                         (DOLLARS IN THOUSANDS)
<S>                                                  <C>        <C>        <C>
PROVED DEVELOPED:
  Oil (MBbls)......................................    17,729      7,465     25,194
  Gas (MMcf).......................................   205,345    104,351    309,696
  Total proved developed (MMcfe)...................   311,719    149,141    460,860
PROVED UNDEVELOPED:
  Oil (MBbls)......................................     4,907      5,112     10,019
  Gas (MMcf).......................................    46,269     29,702     75,971
  Total proved undeveloped (MMcfe).................    75,711     60,374    136,085
TOTAL PROVED RESERVES (MMcfe)......................   387,430    209,515    596,945
Present value of estimated future net cash flows
  before income taxes..............................  $561,303   $269,303   $830,606
</TABLE>

                                       18
<PAGE>   27

                                  RISK FACTORS

     In considering whether to vote in favor of the merger transaction involving
our companies, you should consider all of the information we have included in
this document and its annexes and all of the information included in the
documents we have incorporated by reference. In addition, you should pay
particular attention to the following risks related to the merger and the
combined company.

THE MARKET VALUE OF SHARES OF STONE COMMON STOCK THAT BASIN STOCKHOLDERS RECEIVE
IN THE MERGER WILL VARY AS A RESULT OF THE FIXED EXCHANGE RATIO AND POSSIBLE
STOCK PRICE FLUCTUATIONS.

     The exchange ratio is a fixed ratio that will not be adjusted as a result
of any increase or decrease in the price of either shares of Stone common stock
or shares of Basin common stock. The price of shares of Stone common stock at
the time the merger is completed may be higher or lower than their price on the
date of this document or on the date of the special meetings of stockholders.
Changes in the business, operations or prospects of Stone or Basin, market
assessments of the benefits of the merger and of the likelihood that the merger
will be completed, regulatory considerations, oil and gas prices, general market
and economic conditions, or other factors may affect the prices of shares of
Stone common stock or shares of Basin common stock. Most of these factors are
beyond our control.

     Because the merger will be completed only after the special meetings of our
respective stockholders are held, there is no way to be sure that the price of
the shares of Stone common stock now, or on the date of the special meetings,
will be indicative of its price at the time the merger is completed. We urge you
to obtain current market quotations for both shares of Stone common stock and
shares of Basin common stock.

THERE ARE UNCERTAINTIES IN INTEGRATING OUR BUSINESS OPERATIONS.

     Although the Stone board of directors and the Basin board of directors
considered the potential complementary effects of combining our companies'
assets, personnel and operational expertise, integrating businesses involves a
number of special risks, including:

     - the possibility that management may be distracted from regular business
       concerns by the need to integrate operations,

     - unforeseen difficulties in integrating operations and systems, and

     - problems concerning retaining and assimilating key employees of the
       combined company.

     Any of these could lead to potential adverse short-term or long-term
effects on operating results. As a result, we may not realize any of the
anticipated benefits of the merger.

SIGNIFICANT CHARGES AND EXPENSES WILL BE INCURRED AS A RESULT OF THE MERGER.

     Stone and Basin expect to incur approximately $24 million of costs related
to the merger. These expenses will include severance and related costs upon
completion of the merger, investment banking expenses, legal and accounting
fees, printing expenses, transition and integration costs and other related
charges. See "Interests of Certain Persons in the Merger -- Basin." The
companies may also incur additional unanticipated expenses in connection with
the merger.

STONE'S CERTIFICATE OF INCORPORATION AND BY-LAWS HAVE PROVISIONS THAT DISCOURAGE
CORPORATE TAKEOVERS AND COULD PREVENT STOCKHOLDERS FROM REALIZING A PREMIUM ON
THEIR INVESTMENT.

     Certain provisions of Stone's certificate of incorporation and by-laws and
provisions of the Delaware General Corporation Law may have the effect of
delaying or preventing a change in control. Stone's directors are elected to
staggered terms. Also, Stone's certificate of incorporation authorizes Stone's
board of directors to issue preferred stock without stockholder approval and to
set the rights, preferences and other designations, including voting rights of
those shares as the board may determine. Additional

                                       19
<PAGE>   28

provisions include the availability of authorized but unissued common stock.
These provisions, alone or in combination with each other and with the rights
plan described below, may discourage transactions involving actual or potential
changes of control, including transactions that otherwise could involve payment
of a premium over prevailing market prices to stockholders for their common
stock.

     Stone's board of directors has adopted a stockholder rights plan. The
existence of the rights plan may impede a takeover of Stone not supported by
Stone's board of directors, including a proposed takeover that may be desired by
a majority of our stockholders or involving a premium over the prevailing market
price of Stone's common shares.

SOME OF BASIN'S DIRECTORS AND OFFICERS HAVE INTERESTS IN THE MERGER THAT ARE
DIFFERENT FROM YOUR INTERESTS.

     Some of the directors and officers of Basin are parties to agreements, or
participate in other arrangements, that give them interests in the merger that
are different from your interests. See "Interests of Certain Persons in the
Merger -- Basin" on page 46. Basin stockholders should consider these interests
in connection with their vote on the merger, including whether these interests
may have influenced those directors and officers to recommend or support the
merger.

                                       20
<PAGE>   29

             CAUTIONARY STATEMENT ABOUT FORWARD-LOOKING STATEMENTS

     This document and the documents incorporated by reference contain
forward-looking statements with respect to the merger and the financial
condition, results of operations, plans, objectives, future performance and
business of Stone and Basin. These statements appear in a number of places and
include statements regarding our plans, beliefs or current expectations
including those plans, beliefs and expectations of our officers and directors
with respect to, among other things, future operating results or the ability to
generate income or cash flows.

     These forward-looking statements involve certain risks and uncertainties.
When considering such forward-looking statements, you should keep in mind the
risk factors and other cautionary statements in this document and the documents
incorporated by reference. You should understand that various factors, in
addition to those discussed elsewhere in this document and in the documents
referred to or incorporated by reference in this document, could affect the
future results of the combined company following the merger and could cause
results to differ materially from those expressed in these forward-looking
statements, including the risks described above under "Risk Factors."

     Stone stockholders and Basin stockholders are cautioned not to place undue
reliance on these forward-looking statements, which speak only as of the date of
this document or, in the case of documents incorporated by reference, the dates
of those documents.

     All subsequent written and oral forward-looking statements attributable to
Stone or Basin or any person acting on their behalf are expressly qualified in
their entirety by the cautionary statements contained or referred to in this
section.

                                       21
<PAGE>   30

                              THE SPECIAL MEETINGS

INFORMATION ABOUT THE SPECIAL MEETINGS AND VOTING

     The Stone board of directors is using this document to solicit proxies from
Stone stockholders for use at the Stone special meeting of stockholders. The
Basin board of directors is using this document to solicit proxies from Basin
stockholders for use at the Basin special meeting of stockholders.

TIME AND PLACE OF THE SPECIAL MEETINGS

<TABLE>
<S>                                            <C>
STONE SPECIAL MEETING                          BASIN SPECIAL MEETING
-------------------                            -------------------
            , 2000                             , 2000
       a.m., C.S.T.                            a.m., M.S.T.
PURPOSE OF THE MEETINGS IS TO VOTE THE FOLLOWING ITEMS

A proposal to approve an amendment to Stone's  A proposal to approve the merger agreement
certificate of incorporation to increase the   and the transactions contemplated by the
authorized shares of Stone's common stock      merger agreement, including the merger.
from 25,000,000 shares to             shares.
                                               Such other matters as may properly come
A proposal to approve the issuance of shares   before the Basin special meeting, including
of Stone common stock in the merger, pursuant  the approval of any adjournment or
to the agreement and plan of merger dated      postponement of the Basin special meeting.
October 28, 2000. Approval of the proposal to
amend Stone's certificate of incorporation is
a prerequisite to approval of the proposal
for the share issuance.
Such other matters as may properly come
before the Stone special meeting, including
the approval of any adjournment or
postponement of the Stone special meeting.

RECORD DATE FOR THE SPECIAL MEETINGS

Holders of record of shares of Stone common    Holders of record of shares of Basin common
stock at the close of business on              stock at the close of business on
          will be entitled to vote.                      will be entitled to vote.

OUTSTANDING SHARES HELD ON RECORD DATE

As of the record date, there were              As of the record date, there were
outstanding shares of Stone common stock that  outstanding shares of Basin common stock that
are entitled to notice of, and to vote at,     are entitled to notice of, and to vote at,
the special meeting.                           the special meeting.

SHARES ENTITLED TO VOTE AT THE SPECIAL MEETINGS

Each share of Stone common stock that you own  Each share of Basin common stock that you own
as of the record date entitles you to one      as of the record date entitles you to one
vote.                                          vote.
Shares of Stone common stock deemed            Shares of Basin common stock deemed
beneficially held by Stone or its              beneficially held by Basin or its
subsidiaries will not be voted.                subsidiaries will not be voted.
</TABLE>

                                       22
<PAGE>   31
<TABLE>
<S>                                            <C>
QUORUM REQUIREMENT FOR THE SPECIAL MEETINGS

The presence at the Stone special meeting, in  The presence at the Basin special meeting, in
person or by proxy, of the holders of a        person or by proxy, of the holders of a
majority of the outstanding shares of Stone    majority of the outstanding shares of Basin
common stock is necessary to constitute a      common stock is necessary to constitute a
quorum. If a quorum is not represented at the  quorum. If a quorum is not represented at the
meeting, a vote for adjournment will be taken  meeting, a vote for adjournment will be taken
among the present stockholders or represented  among the present stockholders or represented
by proxy vote for adjournment.                 by proxy vote for adjournment.
Abstentions and broker non-votes count as      Abstentions and broker non-votes count as
present for establishing a quorum. Shares of   present for establishing a quorum. Shares of
Stone common stock held by Stone or its        Basin common stock held by Basin or its
subsidiaries do not count toward a quorum. A   subsidiaries do not count toward a quorum. A
"broker non-vote" occurs with respect to a     "broker non-vote" occurs with respect to a
proposal when a broker is not permitted to     proposal when a broker is not permitted to
vote on that proposal without instruction      vote on that proposal without instruction
from the beneficial owner of the shares of     from the beneficial owner of the shares of
Stone common stock and no instruction is       Basin common stock and no instruction is
given.                                         given.

SHARES BENEFICIALLY OWNED BY STONE AND BASIN DIRECTORS AND EXECUTIVE OFFICERS AS OF THE
RECORD DATE

The directors of Stone are each a party to a   The directors of Basin are each a party to a
voting agreement with Basin under which each   voting agreement with Stone under which each
director has agreed to vote his shares of      director has agreed to vote his shares of
Stone common stock in favor of the amendment   Basin common stock in favor of the merger
to Stone's certificate of incorporation and    agreement and the merger. As of the record
the share issuance. As of the record date,     date, these directors beneficially owned
these directors beneficially owned                  shares of Basin common stock,
shares of Stone common stock, representing     representing approximately   % of the shares
approximately   % of the shares of Stone       of Basin common stock outstanding on that
common stock outstanding on that date.         date.
Stone executive officers (other than those     Basin executive officers (other than those
officers who are also directors) beneficially  officers who are also directors) beneficially
own      shares of Stone common stock. These   own      shares of Basin common stock. These
shares represent approximately   % of the      shares represent approximately   % of the
shares of Stone common stock outstanding as    shares of Basin common stock outstanding as
of the record date. These individuals have     of the record date. These individuals have
indicated that they intend to vote their       indicated that they intend to vote their
shares of Stone common stock in favor of the   shares of Basin common stock in favor of the
Stone proposals.                               merger proposal.
VOTE NECESSARY AT THE SPECIAL MEETINGS TO APPROVE STONE AND BASIN PROPOSALS

Approval of the amendment to Stone's           Approval of the merger agreement and the
certificate of incorporation to increase the   transactions contemplated by the merger
authorized shares of Stone's common stock      agreement, including the merger, requires the
requires the approval of the holders of a      approval of the holders of a majority of the
majority of all outstanding shares of Stone    outstanding shares of Basin common stock.
common stock.
                                               Abstentions and broker non-votes will have
Approval of the share issuance requires the    the same effect as votes against the merger
approval of the holders of a majority of the   proposal.
votes cast on the proposal, provided that the
total votes cast on the proposal represent
over 50% in interest of all outstanding
shares of Stone common stock.
</TABLE>

                                       23
<PAGE>   32
<TABLE>
<S>                                            <C>
Approval of the proposal to amend Stone's
certificate of incorporation is a
prerequisite to approval of the proposal for
the share issuance.
Abstentions and broker non-votes will have
the same effect as votes against each of the
proposals.
</TABLE>

VOTING BY PROXY

     You may vote in person at your special meeting or by proxy. We recommend
you vote by proxy even if you plan to attend your special meeting. You can
always revoke your proxy by changing your vote prior to or at your special
meeting.

     If you are a Basin stockholder, you may vote by proxy card by completing
and mailing the enclosed proxy card or by Internet or telephone by following the
Internet or telephone voting instructions on the proxy card. If you are a Stone
stockholder, you may vote by completing and mailing the enclosed proxy card. If
you properly submit your proxy to us in time to vote, one of the individuals
named as your proxy will vote your common shares as you have directed. You may
vote for or against the proposal or proposals submitted at your special meeting
or abstain from voting.

HOW TO VOTE BY PROXY

<TABLE>
<CAPTION>
            STONE SPECIAL MEETING                          BASIN SPECIAL MEETING
---------------------------------------------  ---------------------------------------------
<S>                                            <C>

  In Writing                                   In Writing
Complete, sign, date and return your proxy     Complete, sign, date and return your proxy
card in the enclosed envelope.                 card in the enclosed envelope.
 By Internet or Telephone                      By Internet or Telephone
Voting by Internet or telephone is not         Go to http://www.eproxy.com and follow the
available to Stone stockholders.               instructions. You will need to give the
                                               personal identification number contained on
                                               your proxy card.
                                               Or, call toll-free 1-800-840-1208 on a
                                               touch-tone telephone 24 HOURS A DAY 7 DAYS A
                                               WEEK. HAVE YOUR PROXY CARD IN HAND. You will
                                               be asked to enter a Control Number or the
                                               personal identification number contained on
                                               your proxy card.
</TABLE>

     THE MEMBERS OF THE STONE BOARD OF DIRECTORS PARTICIPATING IN THE BOARD
DECISION ON THE TRANSACTION UNANIMOUSLY RECOMMEND THAT STONE STOCKHOLDERS VOTE
AT THE SPECIAL MEETING TO APPROVE THE AMENDMENT TO STONE'S CERTIFICATE OF
INCORPORATION TO INCREASE THE AUTHORIZED SHARES OF STONE'S COMMON STOCK AND THE
ISSUANCE OF STONE COMMON STOCK IN CONNECTION WITH THE MERGER. ONE OF STONE'S
DIRECTORS DID NOT PARTICIPATE IN THE BOARD DECISION ON THE TRANSACTION DUE TO AN
AFFILIATION WITH BASIN'S FINANCIAL ADVISOR IN THIS TRANSACTION.

     THE MEMBERS OF THE BASIN BOARD OF DIRECTORS UNANIMOUSLY RECOMMEND THAT YOU
VOTE FOR APPROVAL OF THE MERGER AGREEMENT AND THE TRANSACTIONS CONTEMPLATED BY
THE MERGER AGREEMENT, INCLUDING THE MERGER.

     APPROVAL BY STONE STOCKHOLDERS OF THE AMENDMENT TO STONE'S CERTIFICATE OF
INCORPORATION TO INCREASE THE AUTHORIZED SHARES OF STONE'S COMMON STOCK AND THE
ISSUANCE OF SHARES OF STONE COMMON STOCK, AND APPROVAL BY BASIN STOCKHOLDERS OF
THE MERGER AGREEMENT AND THE TRANSACTIONS CONTEMPLATED BY THE MERGER AGREEMENT,
INCLUDING THE MERGER, ARE CONDITIONS TO CONSUMMATION OF THE MERGER.

                                       24
<PAGE>   33

REVOKING YOUR PROXY

     You may revoke your proxy before it is voted by:

     - submitting a new proxy with a later date, including, if you are a Basin
       stockholder, a proxy given by the Internet or by telephone;

     - notifying your company's Secretary in writing before your special meeting
       that you have revoked your proxy; or

     - voting in person, or notifying the Secretary orally of your wish to
       revoke, at your special meeting.

OTHER VOTING MATTERS

     Voting in Person.  If you plan to attend your special meeting and wish to
vote in person, we will give you a ballot at your special meeting. However, if
your shares of common stock are held in the name of a brokerage firm or trustee,
you must obtain from the firm or trustee an account statement, letter or other
evidence of your beneficial ownership of the common shares.

     People with Disabilities.  We can provide reasonable assistance to help you
participate in your special meeting if you tell us about your disability and
your plan to attend. Please call or write the Secretary of your company at least
two weeks before your special meeting at the number or address provided on page
5.

     Proxy Solicitation.  We will each pay our own costs of soliciting proxies.

     You should submit your proxy without delay by mail or, if you are a Basin
stockholder, by Internet or telephone. We also will reimburse brokers and other
nominees for their expenses in sending these materials to you and getting your
voting instructions.

     DO NOT SEND IN ANY BASIN STOCK CERTIFICATES WITH YOUR PROXY CARDS. THE
EXCHANGE AGENT WILL MAIL TRANSMITTAL FORMS WITH INSTRUCTIONS FOR THE SURRENDER
OF STOCK CERTIFICATES FOR SHARES OF BASIN COMMON STOCK AS SOON AS PRACTICABLE
AFTER THE COMPLETION OF THE MERGER.

OTHER BUSINESS; ADJOURNMENTS AND POSTPONEMENTS

     We currently are not aware of any other business to be acted upon at either
special meeting. If, however, other matters are properly brought before either
special meeting, or any adjourned or postponed special meeting, your proxies
will have discretion to vote or act on those matters according to their best
judgment, including to adjourn the special meeting.

     Adjournments or postponements of the special meetings may be made for the
purpose of, among other things, soliciting additional proxies. Any adjournment
may be made from time to time by approval of the holders of common shares
representing a majority of the votes present in person or by proxy at the
special meeting, whether or not a quorum exists, without further notice other
than by an announcement made at the special meeting.

                                       25
<PAGE>   34

                                   THE MERGER

BACKGROUND OF THE MERGER

     Stone commenced a previous dialogue with Basin in late 1999 that did not
lead to substantive discussions or negotiations. In December 1999, Basin's
President and Chief Executive Officer, Michael S. Smith, met with Stone's
President and Chief Operating Officer, D. Peter Canty, to discuss a possible
strategic combination. At that meeting, Smith advised Canty that Basin was not
for sale. Smith and Canty met again in early January and exchanged certain
preliminary financial information pursuant to mutual confidentiality and
standstill agreements. Later in January, Smith and Canty agreed to terminate all
discussions. No further contacts between Basin and Stone occurred until August
2000.

     Due to a decline in the price of Basin's common stock in early 2000, the
Basin board of directors requested a review of its anti-takeover defenses. At a
meeting of the board of directors of Basin on February 23, 2000, representatives
of Goldman Sachs discussed general market conditions and Basin's position in the
event of an unsolicited takeover proposal.

     At a meeting of the board of directors of Basin on May 11, 2000, the board
reviewed Basin's strategic plan, including the possibility of additional
exploration or acquisitions both in the Gulf of Mexico and onshore. The board
reaffirmed its favorable views of expanding Basin's asset base through
acquisitions and onshore exploration as well as through Gulf of Mexico
exploration, to lower risk and enhance growth potential. The board also noted
the challenging acquisition environment and discussed the possibility of a
strategic business combination. The board noted that the key issue was
determining what would be in the best long-term interests of Basin's
stockholders, and noted that a merger posed potential risks, as well as
opportunities.

     On May 22, 2000, at a meeting of the board of directors of Basin, the board
authorized the engagement of Goldman Sachs, subject to reaching acceptable terms
and conditions, as a financial advisor to Basin and directed management to take
the initial steps to evaluate whether to pursue a business combination and to
identify potential candidates. The process of evaluating potential business
combinations was to be conducted in a manner that would allow Basin to continue
operating on an independent basis and contemplated contacting a modest number of
potential strategic partners. The scope of the services to be provided by
Goldman Sachs pursuant to its engagement included the evaluation of whether or
not Basin should consider a strategic combination and related financial advice
and assistance to Basin in connection with a potential transaction, if
applicable, including structuring and negotiating the financial aspects of such
a transaction, and, if so requested, undertaking a study to enable Goldman Sachs
to render an opinion to the Basin board of directors as to whether the financial
consideration offered in connection with the proposed transaction would be fair
to the Basin stockholders from a financial point of view.

     On June 21, 2000, officers of Basin met with representatives of Goldman
Sachs to review possible merger candidates. On July 17, 2000, Basin retained
Brobeck, Phleger & Harrison LLP as its legal counsel in connection with any
possible business combination.

     On July 18, 2000, Goldman Sachs began to contact a limited number of Gulf
of Mexico operating companies in order to solicit interest in a potential
transaction from the previously identified group of potential business
combination partners, which included Stone. On July 24, 2000, at a meeting of
the Basin board of directors, Smith discussed the recent developments with the
board of directors. Several of the possible strategic merger partners
subsequently signed confidentiality agreements with Basin and participated in
preliminary due diligence presentations with Basin during early August.

     On August 1, 2000, Goldman Sachs approached Stone to solicit its potential
interest in a transaction with Basin. On August 15, 2000, a meeting was held in
Houston at which Basin's management made a presentation about Basin to Stone's
management to assist Stone in considering whether to make a bid to merge with
Basin. Stone and Merrill Lynch analyzed the information made available.

     The Stone board of directors had previously appointed a strategic committee
of selected board members to evaluate any business combination transactions. The
strategic committee met by telephone on
                                       26
<PAGE>   35

August 31, 2000 to approve a proposal to acquire Basin. On August 31, 2000,
Stone submitted a proposal for a stock-for-stock merger.

     After the submission of the original Stone bid, Merrill Lynch and Goldman
Sachs had several telephone conversations regarding the consideration being
offered by Stone and other aspects of Stone's proposal. Goldman Sachs encouraged
Merrill Lynch to have Stone submit a revised proposal. In late August, Basin
received a formal bid from another potential business combination partner.

     On September 9, 2000, Brobeck, Phleger & Harrison distributed an initial
draft of the merger agreement to the other potential business combination
partner and to Stone. In early September, these potential business combination
partners made additional presentations about their companies to the management
of Basin.

     On September 14, 2000, Basin received revised bids and initial comments on
the proposed form of the merger agreement from the potential business
combination partners, including a second proposal from Stone.

     On September 19, 2000, the Basin board held a meeting to discuss the
outstanding offers. Goldman Sachs discussed with the board its analysis of the
offers received by Basin and of each of the proposed merger partners. Brobeck,
Phleger & Harrison reviewed the fiduciary duties owed by Basin's board of
directors to its stockholders in the context of considering a business
combination transaction and presented a summary of the merger agreement and led
a discussion of the key comments delivered by each bidder. At this time, the
Basin board resolved to begin negotiations with a party other than Stone. At the
same time, Basin continued to explore its alternatives with other parties,
including Stone, as well as considering the option to remain independent.

     Goldman Sachs informed Merrill Lynch that Basin was pursuing a proposal
made by another potential acquiror but that if certain legal and business issues
with the other potential acquiror were not resolved, Basin would be willing to
further discuss Stone's proposed offer. No subsequent contact with Stone
occurred until September 27, 2000, when Merrill Lynch was advised that Basin was
willing to pursue negotiations with Stone. On September 28, 2000, Basin
authorized Brobeck, Phleger & Harrison to contact Stone's independent legal
counsel, Vinson & Elkins L.L.P., to commence negotiations on the draft merger
agreement.

     On October 2, 2000, Goldman Sachs discussed revised pricing and other
structural issues with Merrill Lynch. Representatives of Basin, Stone, and their
financial advisors and legal counsel continued to hold discussions on the major
business and legal issues.

     On October 5, 2000, Smith and Canty spoke on the telephone and discussed
key terms. On October 6, 7 and 8, 2000, Stone engineers met with Basin's
independent reserve engineers, Ryder Scott Company, at their offices in Houston
to review Basin's oil and gas reserves and drilling prospects. Stone's legal
advisors also met with Basin's legal advisors during this time at Basin's
offices in Denver. During this period, Smith and Canty also discussed various
employee compensation issues, including a retention plan for Basin employees and
Basin's year-end compensation plans.

     On October 7, 2000, Smith and Canty discussed certain due diligence topics
on a telephone call. Canty then notified Smith that Stone had made what it
believed to be an important discovery on one of its Gulf of Mexico properties.
On October 9, 2000, Smith and Canty discussed in greater detail the due
diligence topics. Canty emphasized the scope and magnitude of Stone's discovery
and indicated that it might affect the terms previously proposed by Stone.

     On October 9, 10 and 11, 2000, Basin conducted due diligence at the offices
of Atwater Consultants, Ltd., Stone's independent reserve engineers, in New
Orleans, Louisiana, and at the offices of Stone, in Lafayette, Louisiana.

     On October 13, 2000, Stone's strategic committee held another meeting and
gave Stone management approval to revise Stone's proposal to Basin. On October
13 and 14, 2000, Smith and Canty discussed several legal and business issues,
including estimates of the costs associated with the merger. On
                                       27
<PAGE>   36

October 14, 2000, Basin held a telephonic board meeting to update the directors
on the status of negotiations with Stone. On October 16, 2000, Smith met with
Canty at the offices of Stone in Houston to discuss valuation issues. Canty
proposed a lower price and Smith informed Canty that the lower offer was
unacceptable.

     On October 17, 18 and 19, 2000, representatives of Merrill Lynch, Stone,
Goldman Sachs and Basin held several discussions regarding the exchange ratio
and related issues. On October 19, 2000, Stone offered to improve the exchange
ratio and Basin agreed to resume negotiations on the merger agreement. In
addition, counsel for both companies continued negotiations on the voting
agreements pursuant to which certain stockholders of each company would agree to
vote in favor of the transaction.

     On October 20, 2000, Stone held a telephonic meeting of its board of
directors. At that meeting, Stone's management described the proposed
transaction, the ongoing negotiations and its overall evaluation of Basin.

     On October 21, 2000, the Basin board held a meeting at which it was
apprised of the recent developments concerning the exchange ratio, and the
outstanding legal issues relating to the merger agreement. On October 23 and 24,
2000, management of Stone and Basin discussed various issues relating to the
merger agreement.

     Members of executive management of Basin and Stone, together with their
respective legal advisors, met several times (either in person or via telephonic
conference) from October 20, 2000 through October 28, 2000 to further negotiate
the terms of the merger agreement. Further due diligence was conducted during
the same period by each of the companies and their respective legal and
financial advisors. These negotiations covered all aspects of the transaction,
including, among other things, the representations and warranties made by the
parties, the restrictions on the conduct of their business, costs of the merger,
the conditions to completion of the proposed merger, the provision regarding
termination, the details of the "no shop" clause, the amount, triggers and
payment of the termination fees and the consequences of termination, and the
delivery and terms of the voting agreements.

     On October 25, 2000, Stone's board met in New Orleans to review the
proposed transaction. Management, Merrill Lynch and Vinson & Elkins made
presentations. The board directed management to continue the negotiations and
agreed to reconvene to make its final determination when the final terms had
been negotiated. The board reviewed and approved the terms of the proposed
voting agreements by each member of the board.

     On October 25, 2000, Basin's board met in Denver to review the proposed
transaction. Management, Goldman Sachs and Brobeck, Phleger & Harrison discussed
the proposed transaction with the board. Goldman Sachs provided their views of
the financial terms of Stone's offer, and counsel reviewed the status of
negotiations on the merger agreement. The board directed management to continue
the negotiations and agreed to reconvene to make its final determination when
the final terms had been negotiated.

     On October 27 and 28, 2000, Canty and Smith discussed key open issues and
agreed on an exchange ratio, subject to approval of each company's board of
directors. Stone's board met in a telephonic meeting, Merrill Lynch presented
its opinion that the exchange ratio was fair from a financial point of view to
Stone and the members of Stone's board participating in the board decision
unanimously approved the transaction, subject to execution of a definitive
agreement.

     During the course of the negotiations between Basin and Stone from late
August 2000 through October 28, 2000, the exchange ratio and other key terms
were actively negotiated. The exchange ratios ranged from a low of .3700 shares
of Stone common stock for one share of Basin common stock to a high ranging
between .4000 and .4360 with a collar based on a Stone share price between $55
and $60. The final exchange ratio was agreed to at .3974.

     On October 28, 2000, Basin's board of directors held two separate meetings
at which the merger agreement, the voting agreements, the affiliate agreements,
the proposed non-competition agreement with

                                       28
<PAGE>   37

Smith and other outstanding issues were discussed at length by the board and
with Basin's management, financial advisor and legal advisors. Basin management
then presented its views of the proposed transaction. Basin's legal counsel
presented a summary of the terms of the merger agreement and discussed various
legal issues with the board. Goldman Sachs presented its financial and valuation
analysis of the transaction and after summarizing its analysis, presented its
oral opinion to the Basin board to the effect that the exchange ratio was fair
to the Basin stockholders, from a financial point of view. Following additional
discussion on the merits of the proposed transaction, the Basin board
unanimously approved the terms of the merger, the merger agreement, the voting
agreements, the affiliate agreements and the transactions contemplated thereby
and agreed to recommend the merger to the stockholders of Basin. During the
meeting, the outside directors of Basin held a discussion, without management
present, at which the terms of the merger, voting and affiliate agreements, the
non-compete agreement of Smith, and the terms of the merger were discussed with
Brobeck, Phleger & Harrison. The outside directors then separately and
unanimously approved the terms of the merger, the merger agreement, the voting
agreements, the affiliate agreements, the proposed non-competition agreement
with Smith, and the transactions contemplated thereby and agreed to recommend
the merger to the stockholders of Basin.

     Following both boards' approval of the merger, Basin and Stone executed the
merger agreement and the directors of each of Basin and Stone executed the
voting agreements.

     On October 30, 2000, Basin and Stone publicly announced in a joint press
release that they had entered into the merger agreement.

REASONS FOR THE MERGER; RECOMMENDATIONS OF THE BOARD OF DIRECTORS

  Stone

     The members of Stone's board of directors participating in the decision on
this transaction have unanimously determined that the merger agreement is fair
to and in the best interest of its stockholders. In reaching its decision to
approve the merger agreement, the Stone board of directors consulted with
Stone's legal and financial advisors, as well as with Stone's management. The
Stone board of directors considered a number of material factors, including:

     - Increased Financial Strength, Critical Mass and Scope.  The merger would
       give Stone increased size, which could allow it to aggressively compete
       for and secure future growth opportunities in the Gulf of Mexico.

     - Expanded Prospect Portfolio.  The merger would expand Stone's existing
       high-impact prospect portfolio with a number of geologically
       opportunistic, multiple-well targets distributed across the shallow-water
       Gulf of Mexico, an area where both companies have achieved high rates of
       return.

     - Enhanced Reserve Growth Potential.  The merger would improve Stone's
       growth reserve potential beyond its current prospect inventory by adding
       22 producing properties and 47 unexplored primary term lease blocks in
       the Gulf of Mexico.

     - Predictable Cash Flows From a Hedge Program.  Stone and Basin each plan
       to enter into commodity hedges that will lock in prices on a portion of
       the production from existing Gulf of Mexico producing properties.

     - Geographic and Risk Diversity.  Basin's Rocky Mountain properties offer a
       second geographic area of operations to complement Stone's primary focus
       area in the Gulf of Mexico. Basin's Rocky Mountain properties add
       geological and risk diversity.

     - Leverage on Existing Expertise and Infrastructure.  The merger would
       enable Stone to use its existing technical and operational expertise
       through its detailed field studies and in-place infrastructure across the
       combined operations in the Gulf of Mexico.

     - Expanded 3-D Seismic Inventory.  The merger would enable Stone to utilize
       Basin's extensive inventory of 3-D seismic databases across the Gulf of
       Mexico.

                                       29
<PAGE>   38

     - Presentation of Financial Advisors.  Merrill Lynch, Stone's financial
       advisor, gave a financial presentation and delivered an opinion to the
       effect that, as of the date of the opinions and based on and subject to
       the matters described in its opinions, the merger consideration was fair,
       from a financial point of view, to Stone's stockholders, as more fully
       described below under "Opinion of Stone's Financial Advisor."

     - Terms and Conditions of Merger.  The terms and conditions of the merger
       agreement and the merger were viewed by the Stone board of directors and
       management as fair to, and in the best interests of, Stone and Stone's
       stockholders.

     - Maintain Leverage Flexibility.  At a time when high commodity prices
       increase the cost of property acquisitions, this stock-for-stock merger
       combines an expanded property base with an increase in reserve potential,
       without incurring debt to finance the acquisition of Basin that could
       limit Stone's future opportunities.

     - Pooling Of Interests Accounting Treatment.  The merger is expected to be
       accounted for as a pooling of interests, which the Stone board believes
       to be more attractive than the purchase method of accounting.

     All combinations, including the merger, also include certain risks and
disadvantages. The material potential risks and disadvantages to Stone's
stockholders identified by the Stone board of directors and management in
considering the merger include the following:

     - the time and resources required to complete the merger, with the
       completion of the merger being subject to various conditions (see "The
       Merger Agreement-Conditions");

     - the difficulties inherent in combining and integrating the two companies
       and the potential distraction to management caused by a transaction of
       this magnitude;

     - as a result of the merger, the benefits of Stone's long-term exploration
       projects would be shared by stockholders of Basin, rather than enjoyed
       solely by Stone's stockholders; and

     - the risk that the benefits sought from the merger might not be fully
       achieved.

     This discussion of the factors considered by the Stone board of directors
is not intended to be exhaustive. Because of the wide variety of factors
considered in connection with its evaluation of the merger, the Stone board of
directors did not find it practicable to, and did not, quantify or otherwise
attempt to assign relative significance to the specific factors considered in
reaching its conclusions. In addition, individual directors may have given
different significance to different factors.

     FOR THE REASONS DISCUSSED ABOVE, THE MEMBERS OF THE STONE BOARD OF
DIRECTORS PARTICIPATING IN THE BOARD DECISION ON THE TRANSACTION HAVE DETERMINED
THAT THE TERMS OF THE MERGER ARE FAIR TO, AND IN THE BEST INTERESTS OF, STONE
AND THE STONE STOCKHOLDERS. ACCORDINGLY, THE MEMBERS OF THE STONE BOARD OF
DIRECTORS PARTICIPATING IN THE BOARD DECISION ON THE TRANSACTION UNANIMOUSLY
RECOMMEND THAT STONE STOCKHOLDERS VOTE AT THE SPECIAL MEETING TO APPROVE THE
AMENDMENT TO STONE'S CERTIFICATE OF INCORPORATION TO INCREASE THE AUTHORIZED
SHARES OF STONE'S COMMON STOCK AND THE ISSUANCE OF STONE COMMON STOCK IN
CONNECTION WITH THE MERGER. ONE OF STONE'S DIRECTORS DID NOT PARTICIPATE IN THE
BOARD DECISION ON THE TRANSACTION DUE TO AN AFFILIATION WITH BASIN'S FINANCIAL
ADVISOR IN THIS TRANSACTION.

  Basin

     Basin's board of directors has unanimously determined that the merger
agreement is consistent with Basin's long-term strategy and fair to and in the
best interests of Basin and its stockholders. Accordingly, the board has
unanimously approved the merger agreement and the transactions contemplated
thereby, including the transactions contemplated by the voting agreements. In
reaching these decisions, Basin's

                                       30
<PAGE>   39

board of directors consulted with senior management, as well as its legal
counsel, independent accountants and financial advisors and considered several
factors, including but not limited to, the following:

     - Creation Of Larger, Better Capitalized Company.  The combined company's
       ability to compete will be substantially enhanced by the merger, which
       will create a larger, better capitalized company, with greater
       operational strengths and exploration and development opportunities.

     - Larger Market Capitalization and Increased Liquidity.  Following the
       transaction, the combined company is expected to have a market
       capitalization of approximately $1.5 billion, based on recent trading
       prices for Stone's common stock. The combined company's common stock will
       be listed for trading on the New York Stock Exchange and it is likely to
       trade in substantially greater volumes and potentially receive higher
       multiples than that of Basin.

     - Risk Reduction and Enhancement of Diversification Plan.  The majority of
       Basin's production arises from a small number of properties concentrated
       in the Gulf of Mexico. Following the transaction, the production value of
       the combined company's properties will be dispersed among a greater
       number of properties. This diversification of operations over a greater
       number of properties is expected to mitigate risks inherent in operating
       a small number of properties in a concentrated area. The combined company
       will also have a larger prospect inventory, which is expected to provide
       the combined company with a greater ability to sustain growth.

     - Complementary Assets.  Basin's operations are concentrated in the Gulf of
       Mexico, a core Stone operating area. The merger will significantly expand
       Stone's operations in this area and will allow Basin's stockholders to
       participate in any future prospects of Stone. The combined company
       expects to benefit from combining its operations in this core operating
       area while also benefiting from greater diversity of properties within
       the Gulf region and the added diversity of operations in the Rocky
       Mountain region.

     - Stronger Pro Forma Financial Profile.  The combined company would have a
       stronger balance sheet than either company individually. Basin's board
       believes that this will result in an improved ability to grow through
       expanded exploration and development drilling programs and through
       acquisitions. The combined entity should also be better capitalized and
       have better access to the U.S. capital markets than Basin as a
       stand-alone entity.

     - Synergies Created By The Merger.  The synergies created by the merger,
       including the opportunities for cost savings and economies of scale, have
       the potential to improve the combined entity's financial condition and
       results of operations.

     - Technical Expertise.  Basin's board and management believe that the
       strength and experience of the combined company will benefit from the
       larger technical talent pool available to the combined company.

     - Premium to Trading Price.  The consideration offered under the
       transaction represented approximately a   % premium over the average
       closing price of Basin's common stock for the           trading days
       preceding the announcement of the merger.

     - Tax Consequences Of The Merger.  The merger is expected to be a tax-free
       reorganization under Section 368 of the Internal Revenue Code. Assuming
       the merger qualifies as a reorganization, the Basin stockholders will not
       generally recognize taxable gain or loss for federal income tax purposes,
       except with respect to cash Basin stockholders will receive instead of
       fractional shares of Stone common stock.

                                       31
<PAGE>   40

     - Pooling Of Interests Accounting Treatment.  The merger is expected to be
       accounted for as a pooling of interests, which the Basin board believes
       to be more attractive than the purchase method of accounting.

     - Opinion Of Financial Advisor.  The Basin board of directors also
       considered the presentation and opinion of Goldman Sachs described below
       to the effect that, based upon its review and assumptions and subject to
       specific matters stated in the opinion, as of October 28, 2000, the
       exchange ratio pursuant to the merger agreement was fair, from a
       financial point of view, to the holders of Basin common stock.

     In reaching its determination to approve the merger for submission to the
stockholders, the Basin board also considered and evaluated information
presented by the management of Basin with respect to the transaction, including
but not limited to:

     - information concerning the results of operations, financial and operating
       performance, financial condition and prospects of and the opportunities
       available to, Stone, Basin and the combined company;

     - the reserves, asset quality and cost structure of Stone and Basin;

     - the strategic and financial alternatives available to Basin;

     - the results and scope of the due diligence review conducted by Basin's
       management and its advisors with respect to Stone's business, properties,
       operations and prospects;

     - information with respect to historical trading prices and trading
       multiples of the common stock of Stone and Basin;

     - information with respect to recent and historical prices and a range of
       potential future price trends of oil and gas; and

     - the terms of the merger agreement.

     The board also considered the option of remaining independent and the
relative merits of the combination with Stone versus remaining independent.

     BASED ON ALL OF THESE MATTERS, AND SUCH OTHER MATTERS AS THE MEMBERS OF THE
BASIN BOARD OF DIRECTORS DEEMED RELEVANT, THE MEMBERS OF THE BASIN BOARD
UNANIMOUSLY APPROVED THE MERGER AND RECOMMEND THE MERGER AGREEMENT AND THE
MERGER FOR APPROVAL TO THE BASIN STOCKHOLDERS.

     The above discussion of the information and factors considered and given
weight by the Basin board is not intended to be exhaustive. However, the Basin
board believes that the discussion includes all material factors it considered.
In reaching the decision to approve and recommend approval to Basin stockholders
of the merger agreement and the merger, the Basin board did not assign any
relative or specific weights to the factors considered. In addition, individual
directors may have given differing weights to different factors.

     The Basin board realized that there are risks associated with the
transaction, including that some of the potential benefits set forth above may
not be realized or that there may be significant costs associated with realizing
such benefits. The Basin board considered that as a result of the merger, the
benefits of Basin's long-term exploration projects would be shared with
stockholders of Stone, rather than enjoyed exclusively by Basin's stockholders.
The Basin board also considered factors such as Stone's ability to retain
Basin's key employees, the volatility of oil and gas prices, the relative
volatility of both companies' stock prices, the uncertainty in estimating oil
and gas reserves, future exploration and development risk and the risks of
conducting business in the Gulf of Mexico. These factors and additional factors
are discussed more fully in this joint proxy statement/prospectus under "Risk
Factors." However, the Basin board believes that the positive factors should
outweigh any negative factors, although the Basin board can give no assurances
in this regard.

                                       32
<PAGE>   41

OPINION OF BASIN'S FINANCIAL ADVISOR

     On October 28, 2000, Goldman Sachs delivered its oral opinion, subsequently
confirmed in writing, to Basin's board of directors that, as of such date, the
exchange ratio was fair from a financial point of view to the holders of Basin
common stock.

     THE FULL TEXT OF THE WRITTEN OPINION OF GOLDMAN SACHS, DATED OCTOBER 28,
2000, WHICH SETS FORTH ASSUMPTIONS MADE, MATTERS CONSIDERED AND LIMITATIONS ON
THE REVIEW UNDERTAKEN IN CONNECTION WITH THE OPINION, IS ATTACHED AS ANNEX B TO
THIS JOINT PROXY STATEMENT/PROSPECTUS AND IS INCORPORATED HEREIN BY REFERENCE.
GOLDMAN SACHS PROVIDED ITS OPINION FOR THE INFORMATION AND ASSISTANCE OF THE
BOARD OF DIRECTORS OF BASIN IN CONNECTION WITH ITS CONSIDERATION OF THE MERGER.
THE GOLDMAN SACHS OPINION DOES NOT CONSTITUTE A RECOMMENDATION AS TO HOW ANY
HOLDER OF BASIN COMMON STOCK SHOULD VOTE WITH RESPECT TO SUCH TRANSACTION. YOU
SHOULD READ THE OPINION IN ITS ENTIRETY.

     In connection with its opinion, Goldman Sachs reviewed, among other things,

     - the agreement and plan of merger;

     - annual reports to stockholders and annual reports on Form 10-K of Basin
       and Stone for the five years ended December 31, 1999;

     - interim reports to stockholders and quarterly reports on Form 10-Q of
       Basin and Stone;

     - other communications from Basin and Stone to their respective
       stockholders;

     - internal financial analyses and forecasts for Basin and Stone prepared by
       their respective managements; and

     - internal financial analyses and forecasts for Basin and Stone prepared by
       the respective management teams, including cost savings and operating
       synergies projected by the management of Basin to result from the merger.

     Goldman Sachs also held discussions with members of the senior management
of Basin regarding its past and current business operations, financial
condition, future prospects and the strategic rationale for, and the potential
benefits of, the merger. In addition, Goldman Sachs:

     - reviewed the reported price and trading activity for Basin common stock
       and Stone common stock;

     - compared financial and stock market information for Basin and Stone with
       similar information for other companies the securities of which are
       publicly traded;

     - reviewed the financial terms of recent business combinations in the
       upstream oil and gas industry specifically and in other industries
       generally; and

     - performed other studies and analyses Goldman Sachs considered
       appropriate.

     Goldman Sachs relied upon the accuracy and completeness of all of the
financial and other information discussed with or reviewed by it and assumed
such accuracy and completeness for purposes of rendering its opinion. Goldman
Sachs assumed, with the consent of Basin, that the internal financial forecasts
prepared by the management of Basin and Stone, including the cost savings and
operating synergies projected by Basin's management to result from the merger
were reasonably prepared on a basis reflecting the best currently available
estimates and judgments of Basin and Stone. Goldman Sachs assumed, with the
consent of Basin, that the merger will be accounted for as a
pooling-of-interests under generally accepted accounting principles. Goldman
Sachs did not make an independent evaluation or appraisal of the assets and
liabilities of Basin or Stone or any of their respective subsidiaries and was
not furnished with any such evaluation or appraisal. With respect to oil and gas
reserve information, Goldman Sachs noted that it is not an expert in the
evaluation of oil and gas properties and Goldman Sachs relied, with the consent
of Basin and without independent verification, solely upon the oil and gas
reserve information and internal estimates prepared by the management of Basin.

                                       33
<PAGE>   42

     The following is a summary of the material financial analyses used by
Goldman Sachs in connection with providing its October 28, 2000 opinion to the
Basin board of directors. Some of the summaries of the financial analyses
include information presented in tabular format. In order to more fully
understand the financial analyses used by Goldman Sachs, the tables must be read
together with the full text of each summary. The tables alone are not a complete
description of Goldman Sachs' financial analyses.

     (1) Comparable Companies Analysis.  Goldman Sachs reviewed and compared
selected financial information, ratios and public market multiples for Basin to
corresponding financial information, ratios and public market multiples for 21
publicly-traded corporations in the upstream oil and gas industry. Goldman Sachs
also reviewed and compared selected financial information, ratios and public
market multiples for Basin to corresponding financial information, ratios and
public market multiples of a subset of the selected companies, focusing on four
companies that have operations focused in the Gulf of Mexico.

     The 21 selected companies were chosen because they are publicly-traded
companies with operations that for purposes of analysis may be considered
similar to certain operations of Basin. Goldman Sachs calculated and compared
various financial multiples and ratios for these companies based on the most
recent publicly available information and, with the exceptions of Basin, Stone
and three other companies, used Goldman Sachs estimates. Goldman Sachs used
management estimates for Basin, Stone and one other company and used other
publicly available research estimates for the two other companies. Multiples and
ratios for each of the selected companies were calculated using closing per
share prices as of October 27, 2000 and multiples and ratios for Basin were
calculated using a per share price of $19.56, the closing market price of the
Basin shares on October 27, 2000, and both Goldman Sachs and management
estimates. With respect to the selected companies, Goldman Sachs considered:

     - closing share price on October 27, 2000 as a percentage of 52-week high
       share price;

     - total debt as a multiple of estimated 2000 discretionary cash flow;

     - share price as a multiple of estimated 2000 and estimated 2001
       discretionary cash flow;

     - enterprise value as a multiple of estimated 2000 and estimated 2001
       unlevered discretionary cash flow; and

     - enterprise value per thousand cubic feet of natural gas equivalent (Mcfe)
       of proved reserves;

     Goldman Sachs calculated both the range and mean of all 21 companies and
the range and mean of the four Gulf of Mexico focused companies, in each case
excluding Basin's financial information and public market multiples. The
following table presents the results of this analysis:

    SELECTED PUBLICLY-TRADED COMPANIES IN THE UPSTREAM OIL AND GAS INDUSTRY

<TABLE>
<CAPTION>
                                                                             GULF OF MEXICO
                                                         RANGE       MEAN     FOCUSED MEAN    BASIN   STONE
                                                      ------------   -----   --------------   -----   -----
<S>                                                   <C>            <C>     <C>              <C>     <C>
October 27, 2000 share price as a percentage of
  52-week high share price..........................       60%-91%     80%         84%          92%     87%
Total debt as a multiple of estimated 2000
  discretionary cash flow...........................     0.0x-2.1x    1.6x        1.0x         0.4x    0.5x
Share price as a multiple of discretionary cash flow
2000 (estimated)....................................     2.3x-9.3x    4.7x        4.5x         3.6x    4.9x
2001 (estimated)....................................     2.7x-7.2x    4.4x        3.8x         3.3x    4.0x
Enterprise value as a multiple of unlevered
  discretionary cash flow
2000 (estimated)....................................     3.8x-8.6x    5.6x        5.1x         4.0x    5.1x
2001 (estimated)....................................     4.0x-7.7x    5.4x        4.3x         3.6x    4.1x
Enterprise value per Mcfe of proved reserves........   $0.86-$7.66   $1.54       $2.27        $1.82   $2.82
</TABLE>

     (2) Selected Transactions Analysis.  Goldman Sachs analyzed certain
information obtained from John S. Herold, Inc. relating to 52 selected
transactions in the upstream oil and gas industry since

                                       34
<PAGE>   43

January 1, 1999. For the purpose of analysis, Goldman Sachs categorized the
transactions by type (corporate or asset) and location (offshore Gulf of Mexico
or Rocky Mountain). Goldman Sachs analyzed three Rocky Mountain upstream
corporate transactions, 24 Rocky Mountain upstream asset transactions, six
offshore Gulf of Mexico upstream corporate transactions and 19 offshore Gulf of
Mexico asset transactions.

     For each of the 52 selected transactions, Goldman Sachs calculated and
compared:

     - consideration paid per barrel of oil equivalent (BOE); and

     - consideration paid per thousand cubic feet of natural gas
       equivalent(Mcfe)of proved reserves.

     The following table presents the results of this analysis, which excludes
one Rocky Mountain upstream corporate transaction from the calculation of means
and medians of the selected Rocky Mountain upstream transactions:

<TABLE>
<CAPTION>
                                         RANGE OF $     MEAN $    MEDIAN $   RANGE OF $     MEAN $    MEDIAN $
                                          PER BOE       PER BOE   PER BOE     PER MCFE     PER MCFE   PER MCFE
                                       --------------   -------   --------   -----------   --------   --------
<S>                                    <C>              <C>       <C>        <C>           <C>        <C>
  Selected Rocky Mountain upstream
    corporate transactions...........    $1.12-$6.23     $4.54     $4.54     $0.19-$1.04    $0.76      $0.76
  Selected Rocky Mountain upstream
    asset transactions...............   $1.97-$29.08     $5.67     $4.44     $0.33-$4.85    $0.95      $0.74
  Selected Rocky Mountain upstream
    transactions as a whole..........   $1.12-$29.08     $5.58     $4.44     $0.19-$4.85    $0.93      $0.74
  Selected Offshore Gulf of Mexico
    upstream corporate
    transactions.....................   $4.10-$12.95     $6.95     $6.19     $0.68-$2.16    $1.16      $1.03
  Selected Offshore Gulf of Mexico
    upstream asset transactions......    $3.07-$8.19     $5.70     $5.75     $0.51-$1.37    $0.95      $0.96
  Selected Offshore Gulf of Mexico
    upstream transactions as a
    whole............................   $3.07-$12.95     $6.00     $5.75     $0.51-$2.16    $1.00      $0.96
</TABLE>

     (3) Historical Acquisition Multiples.  Goldman Sachs analyzed certain
information relating to ten selected business combination transactions announced
in the last three years in the upstream oil and gas industry. Goldman Sachs
calculated and compared for each of the ten selected transactions the enterprise
value per thousand cubic feet of natural gas equivalent (Mcfe) of proved
reserves and the enterprise value as a multiple of LTM EBITDA. The following
table reports the results of this analysis:

<TABLE>
<CAPTION>
                                          RANGES FOR THE               BASIN-STONE
                                       SELECTED TRANSACTIONS   MEAN    TRANSACTION
                                       ---------------------   ----    -----------
<S>                                    <C>                     <C>     <C>
Enterprise value per Mcfe............       $0.68-$1.36        $1.00      $1.98
Enterprise value as a multiple of LTM
  EBITDA.............................         4.9x-9.2x        7.4x        6.8x
</TABLE>

                                       35
<PAGE>   44

     (4) Premiums Paid Analysis.  Goldman Sachs analyzed the average premium
paid in nine upstream corporate transactions. As part of this analysis, Goldman
Sachs calculated the premium to market price one day prior to the announcement
of each transaction, the premium to 30-day weighted average market price prior
to the announcement date and the premium to 60-day weighted average market price
prior to the announcement date. The following table presents the results of
these calculations and assumes that the Basin-Stone transaction was announced on
October 30, 2000:

            SELECTED UPSTREAM CORPORATE TRANSACTIONS (LAST 3 YEARS)

<TABLE>
<CAPTION>
                                                                              BASIN-STONE
                                                        RANGE       AVERAGE   TRANSACTION
                                                     ------------   -------   -----------
<S>                                                  <C>            <C>       <C>
Premium to day prior to announcement date..........  (13.9)%-41.5%    11%        10.0%
Premium to 30 day weighted average prior to
  announcement date................................   (10.5)-56.4     22          8.9
Premium to 60 day weighted average prior to
  announcement date................................   (16.3)-54.2     21         10.6
</TABLE>

     (5) Contribution Analysis.  Goldman Sachs reviewed specific historical and
estimated future operating and financial information based on publicly available
information and estimates provided by the respective managements of Basin and
Stone (each as adjusted by management to the Goldman Sachs research price deck)
to determine the contribution Basin would have made to, among other things, the
combined company's discretionary cash flow, unlevered discretionary cash flow,
net income, production measured by millions of cubic feet of natural gas
equivalent per day (MMcfe/d), the present value of reserves before taxes (PV-10)
measured on October 1, 2000, and equity value and enterprise value, each based
on Basin's share price on October 27, 2000 (the last trading day prior to the
public announcement of the merger).

     The following tables set forth the contribution that Basin would have made
to the combined company:

<TABLE>
<CAPTION>
                                                                 2000         2001
                                                              (ESTIMATE)   (ESTIMATE)
                                                              ----------   ----------
<S>                                                           <C>          <C>
Basin's contribution to the combined company:
  Discretionary Cash Flow...................................      33%          30%
  Unlevered Discretionary Cash Flow.........................      33           30
  Net Income................................................      32           26
  Production (MMcfe/d)......................................      33           31
</TABLE>

<TABLE>
<CAPTION>
                                                                  % OF THE
                                                              COMBINED COMPANY
                                                              ----------------
<S>                                                           <C>
Basin's contribution to the combined company:
  Pre-tax PV-10 Value (total proved) (October 1, 2000)......         36%
  Equity Value..............................................         26
  Enterprise Value..........................................         27
</TABLE>

     (6) Pro Forma Merger Analysis.  Goldman Sachs prepared a pro forma analysis
of the financial impact of the merger using estimates for Stone provided by
Stone's management and estimates for Basin provided by Basin's management (each
as adjusted by management to the Goldman Sachs price deck). Goldman Sachs
compared the discretionary cash flow per share and earnings per share of Basin
on a standalone basis to the discretionary cash flow per share and earnings per
share of the common stock of the combined company on a pro forma basis assuming
that $5 million in annual pre-tax synergies estimated by Basin's management
would be realized following the merger.

                                       36
<PAGE>   45

     Based on such analyses, the merger would be:

     - accretive to Stone's discretionary cash flow per share in each of 2000
       and 2001; and

     - accretive to Stone's earnings per share in 2000 but modestly dilutive to
       Stone's earnings per share in 2001.

     The preparation of a fairness opinion is a complex process and is not
necessarily susceptible to partial analysis or summary description. Selecting
portions of the analyses or of the summary set forth above, without considering
the analyses as a whole, could create an incomplete view of the processes
underlying Goldman Sachs' opinion. In arriving at its fairness determination,
Goldman Sachs considered the results of all such analyses. No company or
transaction used in the above analyses as a comparison is directly comparable to
Basin or Stone or the contemplated transaction. The analyses were prepared for
purpose of Goldman Sachs' providing its opinion to Basin's board of directors
that the exchange ratio was fair from a financial point of view to the holders
of the outstanding shares of Basin common stock. These analyses do not purport
to be appraisals or necessarily reflect the prices at which businesses or
securities actually may be sold. Analyses based upon forecasts of future results
are not necessarily indicative of actual future results, which may be
significantly more or less favorable than suggested by such analyses. Because
such analyses are inherently subject to uncertainty, being based on numerous
factors or events beyond the control of the parties or their respective
advisors, none of Basin, Stone, Goldman Sachs or any other person assumes
responsibility if future results are materially different from those forecast.
As described above, Goldman Sachs' opinion to the Basin board of directors was
one of many factors taken into consideration by the Basin board of directors in
making its determination to approve the merger. The foregoing summary does not
purport to be a complete description of the analyses performed by Goldman Sachs.

     Goldman Sachs, as part of its investment banking business, is continually
engaged in the valuation of businesses and their securities in connection with
mergers and acquisitions, negotiated underwritings, competitive biddings,
secondary distributions of listed and unlisted securities, private placements
and valuations for estate, corporate and other purposes. Goldman Sachs acted as
Basin's financial advisor in connection with, and participated in certain of the
negotiations leading to, the merger agreement. Goldman Sachs is also familiar
with Basin because Goldman Sachs has provided certain investment banking
services to Basin from time to time, including, among other things, acting as
managing underwriter of a public offering of 4,000,000 shares of Basin common
stock in June 1999. Peter K. Barker, an advisory director of Goldman Sachs, is a
director of Stone. Goldman Sachs provides a full range of financial advisory and
securities services and, in the course of its normal trading activities, may
from time to time effect transactions and hold securities, including derivative
securities, of Basin or Stone for its own account and for the accounts of
customers.

     Pursuant to a letter agreement dated September 19, 2000, Basin engaged
Goldman Sachs to act as its exclusive financial advisor to assist Basin in
evaluating a merger or sale of Basin's outstanding common stock or of Basin's
assets. Pursuant to the terms of this engagement letter, Basin has agreed to pay
Goldman Sachs upon consummation of the merger a fee of 1.25% of the aggregate
consideration paid in the merger. Basin also has agreed to reimburse Goldman
Sachs for its reasonable out-of-pocket expenses, including attorneys' fees, plus
any sales, use or similar taxes arising in connection with any matter referred
to in the engagement letter, and to indemnify Goldman Sachs against certain
liabilities, including certain liabilities under the federal securities laws.

OPINION OF STONE'S FINANCIAL ADVISOR

     Stone retained Merrill Lynch to act as its financial advisor in connection
with the merger. On October 28, 2000, Merrill Lynch rendered its oral opinion to
the Stone board of directors, later confirmed in writing, in the Merrill Lynch
fairness opinion letter, that, as of that date and based upon and subject to the
factors and assumptions set forth in the Merrill Lynch fairness opinion letter,
the exchange ratio was fair from a financial point of view to holders of Stone
common stock.

                                       37
<PAGE>   46

     THE FULL TEXT OF THE MERRILL LYNCH FAIRNESS OPINION, WHICH SETS FORTH THE
ASSUMPTIONS MADE, MATTERS CONSIDERED, AND QUALIFICATIONS AND LIMITATIONS ON THE
REVIEW UNDERTAKEN BY MERRILL LYNCH, IS ATTACHED AS ANNEX C TO THIS JOINT PROXY
STATEMENT/PROSPECTUS AND IS INCORPORATED IN THIS DOCUMENT BY REFERENCE. THE
SUMMARY OF THE MERRILL LYNCH FAIRNESS OPINION SET FORTH IN THIS JOINT PROXY
STATEMENT/PROSPECTUS IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO THE FULL TEXT
OF THE OPINION. STOCKHOLDERS OF STONE ARE URGED TO READ THE OPINION IN ITS
ENTIRETY. THE MERRILL LYNCH FAIRNESS OPINION WAS PROVIDED TO THE STONE BOARD FOR
ITS INFORMATION AND IS DIRECTED ONLY TO THE FAIRNESS FROM A FINANCIAL POINT OF
VIEW OF THE EXCHANGE RATIO TO HOLDERS OF STONE COMMON STOCK AND DOES NOT ADDRESS
THE MERITS OF THE UNDERLYING DECISION BY STONE TO ENGAGE IN THE MERGER AND DOES
NOT CONSTITUTE A RECOMMENDATION TO STONE'S STOCKHOLDERS AS TO HOW THE
STOCKHOLDERS SHOULD VOTE ON THE AMENDMENT TO STONE'S CERTIFICATE OF
INCORPORATION OR THE ISSUANCE OF SHARES OF STONE COMMON STOCK IN CONNECTION WITH
THE MERGER OR ANY MATTER RELATED TO THE MERGER. MERRILL LYNCH HAS NOT EXPRESSED
ANY OPINION AS TO THE PRICES AT WHICH STONE COMMON STOCK WILL TRADE FOLLOWING
THE ANNOUNCEMENT OR CONSUMMATION OF THE MERGER.

     Merrill Lynch has consented to the use of Annex C, containing the Merrill
Lynch fairness opinion, in this joint proxy statement/prospectus, and to the
references to Merrill Lynch under the headings "Summary" and "The Merger" in
this joint proxy statement/prospectus. In giving its consent, Merrill Lynch does
not admit that it comes within the category of persons whose consent is required
under Section 7 of the Securities Act or the rules and regulations of the
Commission promulgated thereunder, nor does Merrill Lynch admit that it is an
expert with respect to any part of the Registration Statement in which this
joint proxy statement/prospectus is included, within the meaning of the term
"experts" as used in the Securities Act or the rules and regulations of the
Commission promulgated thereunder.

     The summary set forth below does not purport to be a complete description
of the analyses underlying the Merrill Lynch fairness opinion or the
presentation made by Merrill Lynch to the Stone board. The preparation of a
fairness opinion is a complex and analytical process involving various
determinations as to the most appropriate and relevant methods of financial
analysis and the application of those methods to the particular circumstances
and, therefore, the opinion is not readily susceptible to partial analysis or
summary description. In arriving at its opinion, Merrill Lynch did not attribute
any particular weight to any analysis or factor considered by it, but rather
made qualitative judgments as to the significance and relevance of each analysis
and factor. Accordingly, Merrill Lynch believes that its analyses must be
considered as a whole and that selecting portions of its analyses, without
considering all of its analyses, would create an incomplete view of the process
underlying the Merrill Lynch fairness opinion.

     In performing its analyses, numerous assumptions were made with respect to
industry performance, general business, economic, market and financial
conditions and other matters, many of which are beyond the control of Merrill
Lynch, Basin or Stone. Any estimates contained in the analyses performed by
Merrill Lynch are not necessarily indicative of actual values or future results,
which may be significantly more or less favorable than suggested by the
analyses. Additionally, estimates of the value of businesses or securities do
not purport to be appraisals or to reflect the prices at which the businesses or
securities might actually be sold. Accordingly, the analyses and estimates are
inherently subject to substantial uncertainty. In addition, the requirement for
the delivery of the Merrill Lynch fairness opinion was among several factors
taken into consideration by the Stone board in making its determination to
approve the merger agreement and the transactions contemplated thereby,
including the amendment to Stone's certificate of incorporation to increase the
number of authorized shares of Stone's common stock and the issuance of shares
of Stone common stock in connection with the merger. Consequently, the Merrill
Lynch analyses described below should not be viewed as determinative of the
decision of the Stone board or Stone's management with respect to the fairness
of the exchange ratio.

     In arriving at its opinion, Merrill Lynch, among other things:

          (i) Reviewed selected publicly available business and financial
     information relating to Basin and Stone that Merrill Lynch deemed to be
     relevant, including (a) Annual Reports on Form 10-K and related audited
     financial statements for the fiscal years for the three years ended
     December 31, 1999

                                       38
<PAGE>   47

     and (b) the Quarterly Reports on Form 10-Q and related unaudited financial
     statements for the quarterly periods ending March 31, 2000 and June 30,
     2000;

          (ii) Reviewed the reserve reports prepared as of December 31, 1999 by
     Atwater Consultants, Ltd. and Cawley, Gillespie & Associates, Inc., both
     independent petroleum engineers, for Stone's reserves;

          (iii) Reviewed the reserve report of Ryder Scott Company Petroleum
     Engineers, independent petroleum engineers, for approximately 28% of
     Basin's proved reserve quantities in the Gulf of Mexico as of December 31,
     1999, the audit report by Ryder Scott Company Petroleum Engineers of
     Basin's estimates for Basin's remaining properties as of December 31, 1999,
     and Basin's estimates of Basin's remaining properties as of December 31,
     1999 (collectively, the "Basin Reserve Reports");

          (iv) Reviewed certain information, including production forecasts of
     existing hydrocarbon reserves, and financial forecasts (reviewed using
     identical commodity price assumptions), relating to the business, earnings,
     cash flow, assets, liabilities and prospects of Basin and Stone, furnished
     to Merrill Lynch by Basin and Stone;

          (v) Conducted discussions with members of senior management of Basin
     and Stone concerning the matters described in clauses (i) and (iv) above,
     as well as their respective businesses and prospects before and after
     giving effect to the merger;

          (vi) Reviewed the market prices and valuation multiples for shares of
     Basin common stock and shares of Stone common stock and compared them with
     those of selected publicly traded companies that Merrill Lynch deemed to be
     relevant;

          (vii) Reviewed the results of operations of Basin and Stone and
     compared them with those of selected publicly traded companies that Merrill
     Lynch deemed to be relevant;

          (viii) Compared the proposed financial terms of the merger with the
     financial terms of selected transactions that Merrill Lynch deemed to be
     relevant;

          (ix) Participated in discussions and negotiations among
     representatives of Basin and Stone and their financial and legal advisors;

          (x) Reviewed the potential pro forma impact of the merger;

          (xi) Reviewed a draft of the merger agreement dated October 26, 2000;
     and

          (xii) Reviewed other financial studies and analyses and took into
     account other matters as Merrill Lynch deemed necessary, including Merrill
     Lynch's assessment of general economic, market and monetary conditions.

     In preparing its opinion, Merrill Lynch assumed and relied on the accuracy
and completeness of all information supplied or otherwise made available to
Merrill Lynch, discussed with or reviewed by or for Merrill Lynch, or publicly
available, and Merrill Lynch has not assumed any responsibility for
independently verifying this information or undertaken an independent evaluation
or appraisal of any of the assets or liabilities of Basin or Stone or been
furnished with any evaluation or appraisal. In addition, Merrill Lynch has not
conducted, or assumed any obligation to conduct, any physical inspection of the
properties or facilities of Basin or Stone. With respect to the production and
financial forecast information furnished to or discussed with Merrill Lynch by
Basin or Stone, Merrill Lynch assumed that they had been reasonably prepared
and, at the time of their review, reflected the best available estimates and
judgment of Basin's or Stone's management as to the expected future financial
performance of Basin or Stone, as the case may be, and their respective
petroleum engineers as to their respective reserves, their future hydrocarbon
production volumes and associated costs. Merrill Lynch further assumed that the
merger would be accounted for as a pooling of interests under generally accepted
accounting principles and that it would qualify as a tax-free reorganization for
U.S. federal income tax purposes. Merrill Lynch also

                                       39
<PAGE>   48

assumed that the final form of the merger agreement would be substantially
similar to the last draft reviewed by it.

     Merrill Lynch's opinion is necessarily based upon market, economic and
other conditions as they existed and could be evaluated on, and on the
information made available to Merrill Lynch as of, the date of its opinion.
Merrill Lynch has assumed that in the course of obtaining the necessary
regulatory or other consents or approvals (contractual or otherwise) for the
merger, no restrictions, including any divestiture requirements or amendments or
modifications, will be imposed that will have an adverse effect on the
contemplated benefits of the merger.

     The exchange ratio was determined through analyses of current and projected
financial and operating data by both Stone and Basin and through negotiations
between the president of Stone and the chairman of Basin. After substantial
analysis and consideration, the Stone board approved the amendment to Stone's
certificate of incorporation to increase the authorized shares of Stone's common
stock and the issuance of shares of Stone common stock in connection with the
merger.

     The following is a brief summary of the material analyses performed by
Merrill Lynch in connection with its preparation of the Merrill Lynch fairness
opinion. Some of these summaries of financial analyses include information
presented in tabular format. In order to understand fully the financial analyses
used by Merrill Lynch, the tables must be read together with the text of each
summary. The tables alone do not constitute a complete description of the
financial analyses. Considering the data set forth in the tables without
considering the full narrative description of the financial analyses, including
the methodologies and assumptions underlying the analyses, could create a
misleading or incomplete view of the financial analyses performed by Merrill
Lynch.

  Financial and Production Forecasts

     Basin and Stone provided Merrill Lynch with their respective forecasted
financial and reserve performance based upon a uniform commodity price scenario.
The oil price forecasts were based on the price per barrel ("Bbl") for West
Texas Intermediate crude, and the natural gas price forecasts were based on
NYMEX (Henry Hub, Louisiana delivery) natural gas prices per million British
Thermal Units ("MMBtu"). Natural gas pricing assumed a standard heating value of
one MMBtu per 1,000 cubic feet ("Mcf") of natural gas. Adjustments were made by
both Stone and Basin to the crude oil and natural gas price forecasts to reflect
location and quality differentials. The following table lists the assumed
unadjusted crude oil and natural gas prices provided to Merrill Lynch by Stone
and Basin.

<TABLE>
<CAPTION>
YEAR                                                        OIL ($/BBL)   GAS ($/MMBTU)
----                                                        -----------   -------------
<S>                                                         <C>           <C>
2000 (fourth quarter only)................................    $27.75          $4.70
2001......................................................     25.00           3.50
2002......................................................     25.00           3.50
Thereafter................................................     25.00           3.50
</TABLE>

     Production forecasts and associated production costs were supplied by Basin
and Stone for proved, probable and possible reserves. Operating expenses and
estimated capital expenditures necessary to develop, lift and produce the
proved, probable and possible reserves estimated in the reserve reports were
based on respective management estimates. Adjustments were made by Stone's
management to the assumptions underlying the Basin production forecast in its
unaudited September 30, 2000 reserve report to make the forecast more comparable
with Stone's unaudited reserve report production forecast. An effective tax rate
of 35.0% was assumed for all pro forma adjustments.

  Contribution Analysis

     Using the forecasts described above for both Basin and Stone for the years
2000 and 2001, Merrill Lynch compared the relative projected levels of
discretionary cash flow and earnings before interest, taxes, depreciation,
amortization and exploration expense ("EBITDE") for each company during this
period, as

                                       40
<PAGE>   49

well as the relative level of proved reserves as of December 31, 1999 and
estimated production levels for the year ending December 31, 2000.

     Merrill Lynch also performed a net asset value calculation. Using a
discounted cash flow analysis, Merrill Lynch calculated the present value of the
pre-tax future cash flows that Basin could be expected to generate from their
existing base of proved reserves and risk-adjusted probable and possible
reserves after September 30, 2000 based on Basin projections. These pre-tax cash
flows were discounted at rates ranging from 10% to 12%. Merrill Lynch estimated
Basin's net asset value by adding (i) the risk-adjusted discounted pre-tax cash
flows generated by these proved, probable and possible reserves as estimated by
Basin management plus (ii) an amount determined for undeveloped onshore and
offshore acreage.

     Using a discounted cash flow analysis, Merrill Lynch calculated the present
value of the pre-tax future cash flows that Stone could be expected to generate
from their existing base of proved reserves after September 30, 2000 based on
Stone projections. These pre-tax cash flows were discounted at rates ranging
from 10% to 12%. In addition, the value of Stone's risk-adjusted probable and
possible reserves was estimated by multiplying these reserve volumes by a range
of $1.83/Mcf equivalent to $1.97/Mcf equivalent. Merrill Lynch estimated Stone's
net asset value by adding (i) the risk-adjusted discounted pre-tax cash flows
generated by these proved reserves as estimated by Stone management plus (ii)
the value of risk adjusted probable and possible reserves based on a value per
unit of volume plus (iii) an amount determined for undeveloped onshore and
offshore acreage.

     Relative levels of discretionary cash flow, EBITDE, proved reserves,
estimated production and net asset value calculations were used to develop
implied equity market value contributions. The results of these analyses are set
forth below.

<TABLE>
<CAPTION>
                                                                 STONE'S
                                                                 IMPLIED
                                                                  EQUITY
                                                                  MARKET
                                                                  VALUE
VALUATION BASIS                                                CONTRIBUTION
---------------                                                ------------
<S>                                                            <C>
2000 Discretionary Cash Flow (projected)....................       65.4%
2001 Discretionary Cash Flow (projected)....................       64.9
2000 EBITDE (projected).....................................       66.9
2001 EBITDE (projected).....................................       67.1
Proved Reserves at December 31, 1999........................       65.4
2000 Production (projected).................................       66.5
Net Asset Value as of September 30, 2000....................       72.0
</TABLE>

     The contribution analysis implied an exchange ratio of 0.417 -- 0.524 or a
Stone implied equity market value contribution of 65% -- 70%.

  Comparable Transaction Analysis.

     Merrill Lynch also reviewed publicly available information relating to
comparable merger and acquisition transactions in respect of companies with
primarily exploration and production operations. Merrill Lynch examined the
value of the common equity in each of the transactions as a multiple of last-
twelve-months discretionary cash flow and also examined multiples of the
consideration paid for the common equity and the value of the indebtedness
assumed in each of the transactions to, among other measures, the acquired
companies' EBITDE, proved reserves measured in Mcf equivalent, daily production
measured in barrels of oil equivalent per day ("BOEPD") and the value of future
net cash flows from proved reserves before taxes discounted at 10% as filed with
the Securities Exchange Commission ("Pre-Tax SEC-10").

     The comparable corporate acquisition transactions in the exploration and
production industry that Merrill Lynch reviewed included a total of 18 U.S.
independent exploration and production company corporate acquisitions with
transaction values in excess of $100 million from January 1998 through

                                       41
<PAGE>   50

December 1998, from January 1999 through December 1999 and from January 2000
through October 2000.

     The following table sets forth the results of Merrill Lynch's analysis for
the corporate acquisitions transactions in 1998, 1999 and 2000:

<TABLE>
<CAPTION>
                                    1998                1999                2000
                              -----------------   -----------------   -----------------
                               MEAN     MEDIAN     MEAN     MEDIAN     MEAN     MEDIAN
                              -------   -------   -------   -------   -------   -------
<S>                           <C>       <C>       <C>       <C>       <C>       <C>
Equity market value
  multiples of
  last-twelve-months
  discretionary cash flow...      7.1x      5.6x      5.7x      5.7x      4.9x      4.3x
Enterprise value multiples
  of last-twelve-months
  EBITDE....................      9.0x      6.9x      8.1x      8.1x      7.9x      7.1x
Enterprise value per Mcfe of
  proved reserves...........  $  1.05   $  1.00   $  0.96   $  0.96   $  1.66   $  1.44
Enterprise value per
  BOEPD.....................  $26,333   $25,526   $17,099   $17,099   $28,196   $25,653
Enterprise value multiples
  of Pre-Tax SEC-10.........      1.5x      1.5x      1.7x      1.7x      1.5x      1.5x
</TABLE>

     Merrill Lynch also reviewed publicly available information relating to
comparable asset acquisition transactions from 1997 to October 2000 in three
distinct geographic areas:

     - Gulf Coast -- Offshore (28 transactions);

     - Rocky Mountains (23 transactions);

     - Gulf Coast -- Onshore (37 transactions).

Merrill Lynch examined the multiples of the consideration paid for the acquired
assets, including the value of the indebtedness, if any, assumed, among other
measures, proved reserves measured in Mcf equivalent and daily productive
measured in BOEPD. The following table sets forth the results of Merrill Lynch's
analysis of these asset acquisition transactions:
<TABLE>
<CAPTION>
                                                    GULF COAST -- OFFSHORE                  ROCKY MOUNTAINS
                                               --------------------------------     --------------------------------
                                                   MEAN              MEDIAN             MEAN              MEDIAN
                                                   ----              ------             ----              ------
<S>                                            <C>                <C>               <C>                <C>
Enterprise value per Mcfe of proved
  reserves...................................  $        1.03      $        1.04     $        0.71      $        0.74
Enterprise value per BOEPD...................  $      15,214      $      14,561     $      19,083      $      20,704

<CAPTION>
                                                    GULF COAST -- ONSHORE
                                               --------------------------------
                                                   MEAN              MEDIAN
                                                   ----              ------
<S>                                            <C>                <C>
Enterprise value per Mcfe of proved
  reserves...................................  $        0.95      $        0.86
Enterprise value per BOEPD...................  $      20,013      $      19,779
</TABLE>

     These analyses indicated that, with respect to the acquisition of Basin,
the relevant equity value multiples for 2000 estimated discretionary cash flow
range from 4.5x to 5.5x. Further, this analysis indicated that, with respect to
the acquisition of Basin, the relevant enterprise value multiples of 2000
estimated EBITDE range from 5.0x to 6.0x, and price per Mcfe of 1999 and 2000
estimated proved reserves range from $1.40 to $1.60. In addition, this analysis
indicated that, with respect to the acquisition of Basin, the relevant
enterprise value multiples for 1999 and current daily production range from
$23,000 to $28,000. From the equity value and enterprise value ranges implied by
these multiple ranges, Merrill Lynch determined a composite enterprise value
range for Basin under this method of $450 million to $550 million, or an equity
market value range of $400 million to $500 million.

     The comparable transaction analysis implied an exchange ratio of
0.365-0.456 or a Stone implied equity market value contribution of 68%-73%.

     Because the reasons for, and circumstances surrounding, each of the
comparable transactions analyzed were so diverse and due to the inherent
differences between the operations and financial conditions of Basin and the
selected companies, Merrill Lynch believes that a purely quantitative comparable
transaction analysis would not be dispositive in the context of the merger.
Merrill Lynch further believes that an appropriate use of a comparable
transaction analysis in this instance involves qualitative judgments

                                       42
<PAGE>   51

concerning the differences between the characteristics of these transactions and
the merger that would affect the value of the acquired companies and businesses
and Basin, those judgments being reflected in Merrill Lynch's opinion.

  Comparable Company Trading Analysis

     Merrill Lynch reviewed and compared selected financial information, ratios
and public market multiples derived from the Stone projections to corresponding
financial information, ratios and public market multiples for ten publicly
traded corporations in the oil and gas exploration, development and production
industry:

<TABLE>
<S>                                         <C>
- Barrett Resources Corporation             - Newfield Exploration Company
- Cross Timbers Oil Company                 - Pogo Producing Company
- Forest Oil Corporation                    - The Houston Exploration Company
- Louis Dreyfus Natural Gas Corp.           - Triton Energy Limited
- Mitchell Energy & Development Corp.       - Vintage Petroleum, Inc.
</TABLE>

     These Stone selected companies were chosen because they are publicly traded
companies with financial and operating characteristics that Merrill Lynch deemed
to be similar to those of Stone, including, among other things, equity market
capitalization, Gulf Coast Basin focus and natural gas bias. Merrill Lynch
calculated various financial ratios for the selected companies and compared them
to those calculated for Stone. The ratios for the selected companies were based
on publicly available information, including estimates provided by Merrill Lynch
research and the Institutional Brokers Estimate System. Merrill Lynch calculated
the following financial ratios:

     - equity market value multiples of:

      - 2000 estimated discretionary cash flow and

      - 2001 estimated discretionary cash flow; and

     - enterprise value (defined as market value of common equity plus book
       value of debt less cash) multiples of:

      - 2000 estimated EBITDE

      - 2001 estimated EBITDE

      - proved reserves as of December 31, 1999

      - average daily production (measured in BOEPD) for the year ended December
31, 1999 and

      - Pre-Tax SEC-10 at December 31, 1999.

     The following table shows the mean and median, as well as the relevant
range, for the results of these calculations for the selected companies:

<TABLE>
<CAPTION>
FINANCIAL MEASURE                                   MEAN     MEDIAN    RELEVANT RANGE
-----------------                                  -------   -------   ---------------
<S>                                                <C>       <C>       <C>
2000 Discretionary Cash Flow (projected).........     4.9x      4.6x         5.0x-5.5x
2001 Discretionary Cash Flow (projected).........     4.7x      4.5x         4.8x-5.3x
2000 EBITDE (projected)..........................     5.3x      5.1x         5.5x-6.0x
2001 EBITDE (projected)..........................     5.3x      5.1x         5.0x-5.5x
Reserve value ($/Mcfe)...........................    $1.73     $1.56       $1.60-$1.90
Value per BOEPD..................................  $38,321   $36,128   $38,500-$42,500
1999 Pre-Tax SEC-10 Value........................     1.6x      1.7x         1.7x-1.9x
</TABLE>

                                       43
<PAGE>   52

     From the equity value and enterprise value ranges implied by these multiple
ranges, Merrill Lynch determined a composite enterprise value range for Stone
under this method of $1,100 million to $1,200 million, or an equity market value
range of $1,050 million to $1,150 million.

     None of the selected companies are identical to Stone. Accordingly, an
analysis of the results of the foregoing is not purely mathematical. Rather, it
involves complex considerations and judgments concerning differences in
financial and operating characteristics of the selected companies and other
factors that could affect the public trading value of the comparable companies
or company to which Stone was being compared.

     Merrill Lynch reviewed and compared selected financial information, ratios
and public market multiples derived from the Basin projections to corresponding
financial information, ratios and public market multiples for eight publicly
traded corporations in the oil and gas exploration, development and production
industry:

<TABLE>
<S>                                         <C>
- Cabot Oil & Gas Corporation               - EEX Corporation
- The Houston Exploration Company           - HS Resources, Inc.
- The Meridian Resource Corporation         - Nuevo Energy Company
- Swift Energy Company                      - Tom Brown, Inc.
</TABLE>

     These selected companies were chosen because they are publicly traded
companies with financial and operating characteristics that Merrill Lynch deemed
to be similar to those of Basin, including, among other things, equity market
capitalization, natural gas bias and Gulf Coast Basin and Rocky Mountain
production. Merrill Lynch calculated various financial ratios for these selected
companies and compared them to those calculated for Basin. The ratios for the
selected companies were based on publicly available information, including
estimates provided by Merrill Lynch research and the Institutional Brokers
Estimate System. Merrill Lynch calculated the following financial ratios:

     - equity market value multiples of:

      - 2000 estimated discretionary cash flow and

      - 2001 estimated discretionary cash flow; and

     - enterprise value (defined as market value of common equity plus book
       value of debt less cash) multiples of:

      - 2000 estimated EBITDE

      - 2001 estimated EBITDE

      - proved reserves as of December 31, 1999

      - average daily production (measured in BOEPD) for the year ended December
        31, 1999 and

      - Pre-Tax SEC-10 at December 31, 1999.

     The following table shows the mean and median, as well as the relevant
range, for the results of these calculations for the selected companies.

<TABLE>
<CAPTION>
FINANCIAL MEASURE                                   MEAN     MEDIAN    RELEVANT RANGE
-----------------                                  -------   -------   ---------------
<S>                                                <C>       <C>       <C>
2000 Discretionary Cash Flow (projected).........     4.1x      3.9x         4.0x-4.5x
2001 Discretionary Cash Flow (projected).........     3.7x      3.7x         3.8x-4.3x
2000 EBITDE (projected)..........................     5.5x      5.4x         5.0x-5.5x
2001 EBITDE (projected)..........................     5.1x      4.9x         4.5x-5.0x
Reserve value ($/Mcfe)...........................  $  1.50   $  1.78       $1.50-$1.80
Value per BOEPD..................................  $32,627   $31,910   $31,500-$33,500
1999 Pre-Tax SEC-10 Value........................     1.4x      1.4x         1.5x-1.8x
</TABLE>

                                       44
<PAGE>   53

     From the equity value and enterprise value ranges implied by these multiple
ranges, Merrill Lynch determined a composite enterprise value range for Basin
under this method of $475 million to $550 million or an equity market value
range of $425 million to $500 million.

     None of the selected companies is identical to Basin. Accordingly, an
analysis of the results of the foregoing is not purely mathematical. Rather, it
involves complex considerations and judgments concerning differences in
financial and operating characteristics of the selected companies and other
factors that could affect the public trading value of the comparable companies
or company to which Basin was being compared.

     The comparable company trading analysis implied an exchange ratio of
0.420-0.450 or a Stone implied equity market value contribution of 68%-70%.

  Merger Premium Analysis

     In order to determine an implied exchange ratio range based upon a merger
premium analysis, Merrill Lynch examined premiums paid for the target's equity
value per share over pre-announcement stock prices one day prior to
announcement, 30 days prior to announcement and 60 days prior to announcement in
corporate exploration and production company merger transactions with an
transaction value in the range of $200 million to $1 billion for the period of
1994 to present.

     The following table shows the mean and median for the acquisition premiums
paid over the target's stock price for one day, thirty days and sixty days prior
to the announcement.

<TABLE>
<CAPTION>
   ONE DAY      THIRTY DAYS    SIXTY DAYS
-------------  -------------  ------------
MEAN   MEDIAN  MEAN   MEDIAN  MEAN  MEDIAN
-----  ------  -----  ------  ----  ------
<S>    <C>     <C>    <C>     <C>   <C>
18.1%..  14.9% 22.7%   21.6%  23.2%  23.8%
</TABLE>

     The merger premium analysis implied a relevant premium range of 18% to 23%,
resulting in an implied exchange ratio of 0.406-0.423 or a Stone implied equity
market value contribution of 70%-71%.

     Because the reasons for, and circumstances surrounding, each of the
transactions analyzed were different, Merrill Lynch believes that a purely
quantitative merger premium analysis would not be dispositive in the context of
the merger. Merrill Lynch further believes that an appropriate use of a merger
premium analysis in this instance involves quantitative judgments concerning the
differences between the characteristics of these transactions and the merger
that would affect the value of Basin and Stone, which judgments are reflected in
Merrill Lynch's opinion.

  Historical Implied Exchange Ratio Analysis

     Using closing stock prices for Stone and Basin at October 24, 2000, as well
as average closing stock prices for both companies for the periods 30, 60, 90,
180 days, and one year and two years prior to October 24, 2000, Merrill Lynch
derived equity market valuations for Stone and Basin based on each of these
average closing stock prices. The relative levels of these equity market
valuations were then used to derive implied exchange ratios.

     The historical implied exchange ratio analysis implied an exchange ratio of
0.340-0.390 or a Stone implied equity market value contribution of 71%-74%.

  Merger Consequences

     For both Stone's projections and Basin's projections, Merrill Lynch
analyzed the respective contributions of each of Stone and Basin to the
estimated net income and discretionary cash flow of the combined company giving
effect to the merger on a pro forma basis for the years 2000, 2001 and 2002 and
analyzed the increase or decrease in net income and discretionary cash flow per
Stone share resulting from the merger. The foregoing analysis indicated the
following effects on net income and discretionary cash

                                       45
<PAGE>   54

flow per Stone share, before one-time merger related costs and expenses and
after pre-tax annual consolidation savings of $2.5 million in 2001 and $5.0
million in 2002:

<TABLE>
<CAPTION>
                                                              ACCRETION
                                                              (DILUTION)
                                                              ----------
<S>                                                           <C>
2000 Net Income (projected).................................      7.1%
2000 Discretionary Cash Flow (projected)....................      9.0
2001 Net Income (projected).................................      2.7
2001 Discretionary Cash Flow (projected)....................      9.7
2002 Net Income (projected).................................      9.8
2002 Discretionary Cash Flow (projected)....................     16.6
</TABLE>

  Merrill Lynch Financial Advisor Fee

     Pursuant to an engagement letter dated September 15, 2000, Stone retained
Merrill Lynch to act as its financial advisor in connection with the merger.
Pursuant to the engagement letter, Stone has agreed to pay Merrill Lynch a fee
of $3,500,000 for services rendered in connection with the merger. In addition,
if the merger agreement is terminated under circumstances pursuant to which a
termination fee is paid to Stone, Stone has agreed to pay Merrill Lynch a fee of
25% of any termination fee, subject to a maximum payment of $2,000,000, for its
services. Stone also has agreed to reimburse Merrill Lynch for the expenses
reasonably incurred by it in entering into and performing services by it in
connection with its engagement (including reasonable counsel fees) and to
indemnify Merrill Lynch and its affiliates and their respective officers,
directors, employees, agents and controlling persons against certain expenses,
losses, claims, damages or liabilities in connection with its services performed
in connection with its engagement, including liabilities under federal
securities laws. Stone has also agreed to reimburse Merrill Lynch for its
reasonable out-of-pocket expenses, including reasonable fees and disbursements
of its legal counsel.

     Stone retained Merrill Lynch based upon Merrill Lynch's experience and
expertise. Merrill Lynch is an internationally recognized investment banking and
advisory firm. Merrill Lynch, as part of its investment banking business, is
continuously engaged in the valuation of businesses and securities in connection
with mergers and acquisitions, negotiated underwritings, competitive biddings,
secondary distributions of listed and unlisted securities, private placements
and valuations for corporate and other purposes. Merrill Lynch has in the past
provided financial advisory and/or financing services to Stone, including lead
managing Stone's common stock offering in August 1999, and may continue to do so
and has received, and may receive, fees for the rendering of these services. In
the ordinary course of its business, Merrill Lynch and its affiliates may
actively trade the debt and equity securities of Stone and Basin (and anticipate
trading after the merger in the securities of Stone) for their own accounts and
for the accounts of customers and, accordingly, may at any time hold a long or
short position in these securities.

INTERESTS OF CERTAIN PERSONS IN THE MERGER

  Basin

     In considering the recommendation of the Basin board of directors with
respect to the merger, you should be aware that some executive officers and
directors of Basin have interests in the merger which will provide them with
benefits that are in addition to their interests as a shareholder of Basin
generally. The Basin board of directors was aware of the potential conflicts
discussed below and considered them in approving the merger.

     Pursuant to their respective employment or other "change of control" type
agreements, the following Basin officers are entitled to receive the benefits
described below. The merger will constitute a "change of control" for purposes
of such agreements.

     - Michael S. Smith, President, Chief Executive Officer and Director. Mr.
       Smith will receive a payment equal to three times the sum of (i) his base
       salary of $385,200 plus (ii) his average bonus

                                       46
<PAGE>   55
      for the last two years, to be paid over 12 months or, if Mr. Smith elects,
      in a lump sum, discounted to present value, if he resigns for good reason
      following the merger. Mr. Smith is not entitled to the accelerated vesting
      of any equity securities he holds at the time of termination, except as
      may apply with respect to his performance share awards. Mr. Smith's 55,000
      shares of common stock subject to earnout schedules pursuant to the
      outstanding performance share awards under Basin's performance share plan
      will be earned as described below in "Interests of Certain Persons in the
      Merger -- Basin -- Performance Share Awards." Mr. Smith will also be
      entitled to certain severance benefits if his employment is terminated
      without cause following the merger.

     - Neil L. Stenbuck, Vice President, Chief Financial Officer and Director.
       Mr. Stenbuck will receive a lump sum payment of three times the sum of
       (i) his base salary of $246,100 and (ii) the higher of his average bonus
       for the previous three years or his bonus for the most recently completed
       fiscal year after the merger if his employment is terminated without
       cause by Basin or its successor company or he resigns for good reason at
       any time during the employment period following the merger, of if he
       resigns for any reason within 30 days after the merger. Unvested options
       for 53,750 shares of Basin common stock held by Mr. Stenbuck with a
       weighted average exercise price of $12.98 per share will vest under the
       circumstances described above and will be exercisable to purchase Stone
       common shares until the earlier to occur of twelve months after his
       employment is terminated or ten years from the date of original grant.
       The restrictions on all 15,000 of Mr. Stenbuck's outstanding performance
       share awards issued under Basin's performance share plan will be
       eliminated upon consummation of the merger and his termination or
       resignation as described above pursuant to the applicable
       change-in-control provisions.

     - Howard L. Boigon, Vice President, General Counsel and Director. Mr.
       Boigon will receive a lump sum payment of three times the sum of (i) his
       base salary of $207,740 and (ii) the higher of his average bonus for the
       previous three years or his bonus for the most recently completed fiscal
       year after the merger if his employment is terminated without cause by
       Basin or its successor company or he resigns for good reason at any time
       during the employment period following the merger, or if he resigns for
       any reason within 30 days of the merger. Unvested options for 53,750
       shares of Basin common stock held by Mr. Boigon with a weighted average
       exercise price of $12.98 per share will vest under the circumstances
       described above and will be exercisable to purchase Stone common shares
       until the earlier to occur of twelve months after his employment is
       terminated or ten years from the date of original grant. The restrictions
       on all 15,000 of Mr. Boigon's outstanding performance share awards issued
       under Basin's performance share plan will be eliminated upon consummation
       of the merger and his termination or resignation as described above
       pursuant to the applicable change-in-control provisions.

     - Thomas J. Corley, Vice President, Engineering and Production. Mr. Corley
       will receive a lump sum payment of three times the sum of (i) his base
       salary of $160,500 and (ii) the higher of his average bonus for the
       previous three years or his bonus for the most recently completed fiscal
       year after the merger if his employment is terminated without cause by
       Basin or its successor company or he resigns for good reason at any time
       during the employment period following the merger, of if he resigns for
       any reason within 30 days of the merger. Unvested options for 53,750
       shares of Basin common stock held by Mr. Corley with a weighted average
       exercise price of $12.98 per share will vest under the circumstances
       described above and will be exercisable to purchase Stone common shares
       until the earlier to occur of twelve months after his employment is
       terminated or ten years from the date of original grant. The restrictions
       on all 15,000 of Mr. Corley's outstanding performance share awards issued
       under Basin's performance share plan will be eliminated upon consummation
       of the merger and his termination or resignation as described above
       pursuant to the applicable change-in-control provisions.

     - Patrick A. Jackson, Vice President, Onshore Exploration. Mr. Jackson will
       receive a lump sum payment of three times the sum of (i) his base salary
       of $176,800 and (ii) a bonus equal to his average annualized bonus if his
       employment is terminated without cause by Basin or its successor company
       or he resigns for good reason at any time during the employment period
       following the
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<PAGE>   56

merger. Unvested options for 60,000 shares of Basin common stock held by Mr.
Jackson with a weighted average exercise price of $12.51 per share will vest
under the circumstances described above and will be exercisable to purchase
      Stone common shares for three months following termination of his
      employment. Mr. Jackson's 10,000 shares of common stock subject to earnout
      schedules pursuant to the outstanding performance share awards under
      Basin's performance share plan will be earned as described below in
      "Interests of Certain Persons in the Merger -- Basin -- Performance Share
      Awards."

     - Dalton F. Polasek, Vice President, Gulf Coast Engineering. Mr. Polasek
       will receive a lump sum payment of three times the sum of (i) his base
       salary of $155,150 and (ii) the higher of his average bonus for the
       previous three years or his bonus for the most recently completed fiscal
       year after the merger if his employment is terminated without cause by
       Basin or its successor company or he resigns for good reason at any time
       during the employment period following the merger, of if he resigns for
       any reason within 30 days after the merger. Unvested options for 56,750
       shares of Basin common stock held by Mr. Polasek with a weighted average
       exercise price of $12.21 per share will vest under the circumstances
       described above and will be exercisable to purchase Stone common shares
       until the earlier to occur of twelve months after his employment is
       terminated or ten years from the date of original grant. The restrictions
       on all 15,000 of Mr. Polasek's outstanding performance share awards
       issued under Basin's performance share plan will be eliminated upon
       consummation of the merger and his termination or resignation as
       described above pursuant to the applicable change-in-control provisions.

     - David A. Pustka, Vice President, Gulf Coast Exploration. Mr. Pustka will
       receive a lump sum payment of three times the sum of (i) his base salary
       of $174,590 and (ii) a bonus equal to his average annualized bonus if he
       resigns following the merger. Unvested options for 65,000 shares of Basin
       common stock held by Mr. Pustka with a weighted average exercise price of
       $12.69 per share will vest under the circumstances described above and
       will be exercisable to purchase shares of Stone common stock for three
       months following termination of his employment. The restrictions on all
       15,000 of Mr. Pustka's outstanding performance share awards issued under
       Basin's performance share plan will be eliminated upon consummation of
       the merger and his termination as described above pursuant to the
       applicable change-in-control provisions. Mr. Pustka will also be entitled
       to certain severance benefits if his employment is terminated without
       cause following the merger.

     - Samual D. Winegrad, Vice President, Corporate Development. Mr. Winegrad
       will receive a lump sum payment of three times the sum of (i) his base
       salary of $160,500 and (ii) the higher of his average bonus for the
       previous three years on his bonus for the most recently completed fiscal
       year after the merger if his employment is terminated without cause by
       Basin or its successor company or he resigns for good reason at any time
       during the employment period following the merger, or if he resigns for
       any reason within 30 days after the merger. Unvested options for 43,750
       shares of Basin common stock held by Mr. Winegrad with a weighted average
       exercise price of $13.51 per share will vest under the circumstances
       described above and will be exercisable to purchase Stone common shares
       until the earlier to occur of twelve months after his employment is
       terminated or ten years from the date of original grant. The restrictions
       on all 15,000 of Mr. Winegrad's outstanding performance share awards
       issued under Basin's performance share plan will be eliminated upon
       consummation of the merger and his termination as described above
       pursuant to the applicable change-in-control provisions.

     Additionally, Mr. Smith, the current chief executive officer of Basin, has
agreed to enter into a confidentiality and non-compete agreement with Stone in
connection with the merger. In exchange for Mr. Smith's confidentiality and
non-compete agreement Stone will pay Mr. Smith $300,000 per year for each of the
next three (3) years following completion of the merger.

     Performance Share Awards.  Immediately prior to the effective time of the
merger, there will be approximately 155,000 shares of Basin common stock subject
to earn-out schedules pursuant to the outstanding performance share awards under
the Performance Share Plan. The restrictions on all such
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<PAGE>   57

performance shares held by Messrs. Stenbuck, Boigon, Corley, Polasek, Pustka and
Winegrad will be eliminated upon consummation of the merger and such
individual's termination or resignation as described above pursuant to their
applicable change-in-control provisions; provided, however, that if such
individual's termination or resignation does not occur in connection with the
merger, such individual's award will be determined pursuant to the following two
sentences. With respect to the awards held by Messrs. Smith and Jackson and any
individuals listed in the preceding sentence who did not terminate or resign in
connection with the merger, such awards will be earned or forfeited as
determined prior to the effective time of the merger in accordance with the
change-in-control provisions of such holder's share awards. However, any shares
not earned based on the most recently issued year-end financial statement prior
to the effective time shall be earned as determined prior to the effective time
by Basin's compensation and incentive committee under the Performance Share Plan
(and subject to the prior approval of Stone) based on the financial performance
of Basin during the period beginning on the first day of the fiscal year in
which the effective time of the merger occurs and ending on the closing date of
the merger.

     Director Nomination.  Under the terms of the Merger Agreement, Stone has
agreed to cause Michael S. Smith to become a member of Stone's Board of
Directors as of the Effective Time. Mr. Smith will be a Class II Director whose
initial term shall expire in 2001. Stone has agreed to nominate Mr. Smith for
re-election to Stone's Board of Directors, which election is expected to take
place at Stone's annual meeting of stockholders in 2001.

     Voting Agreements.  Stockholders of Basin holding approximately 14.6% of
Basin's outstanding stock and stockholders of Stone holding approximately 15.7%
of Stone's outstanding stock have entered into voting agreements, pursuant to
which such stockholders have agreed to vote for the merger.

     Indemnification Arrangements.  Under the merger agreement, Stone has agreed
to, and to cause the surviving corporation in the merger to, indemnify and hold
harmless each present and former officer and director of Basin against any
costs, expenses, judgments, fines, losses, claims, damages, liabilities or
amounts paid in settlement, arising out of or pertaining to matters existing or
occurring at or prior to the effective time of the merger to the fullest extent
Basin would have been permitted under the DGCL and its certificate of
incorporation or by-laws on the date of the merger agreement.

     Insurance.  For a period of six years after the effective time of the
merger, Stone has agreed to cause the surviving corporation to maintain
directors' and officers' liability insurance covering the persons who are
covered as of the date of the merger agreement by Basin's directors' and
officers' liability insurance policy provided that Stone is not required to pay
more than 200% of the premium currently paid by Basin for such coverage.

     Financial Advisory Fee.  Goldman, Sachs & Co. has been retained by Basin as
a financial advisor in connection with the merger, for which Goldman, Sachs &
Co. will be paid a fee of approximately 1.25% of the aggregate consideration
paid in the merger upon consummation of the merger.

  Stone

     One of Stone's directors, Peter K. Barker, is an advisory director of
Goldman Sachs, Basin's is financial advisor. Mr. Barker did not participate in
the board decision on this transaction.

EFFECTS OF GOLDEN PARACHUTE TAX RULES

     The accelerated vesting of options and restricted share awards, whether at
the time of the merger or upon the subsequent termination of the above Basin
officers' employment, and payment of the severance benefits (three times salary
and bonus) to which one of the above officers of Basin may become entitled in
connection with such termination could, under certain circumstances, be at a
sufficiently high level to cause those benefits to be considered parachute
payments under Section 280G(b)(2)(A) of the Internal Revenue Code. Such
parachute payments will actually result if the combined parachute value of those
accelerated vesting benefits and severance payments exceeds 2.99 times the
individual's average W-2 wages for the five calendar years (or lesser number of
years of actual employment with Basin) preceding the

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<PAGE>   58

calendar year in which the merger occurs. The parachute value of each of those
benefits will be specially calculated for parachute payment purposes under the
proposed Treasury Regulations issued under Section 280G of the Internal Revenue
Code. If the resulting value exceeds the 2.99 limit, then an excess parachute
payment will result under the Internal Revenue Code to the extent that such
value exceeds one times the individual's average W-2 wages for those years (the
"base amount").

     In such event, a portion of the base amount will be allocated to each of
such officer's parachute payments in the same proportion as the value of each
particular payment (whether the parachute value attributed to the accelerated
vesting of his stock options or restricted shares or the parachute value of his
severance payments) bears to the total parachute value of all those parachute
payments. To the extent the parachute value attributed to the accelerated
vesting of his options or restricted shares of the parachute value of his
severance payments exceeds the portion of the base amount allocated to that
particular parachute payment, an excess parachute payment will arise, and the
deduction otherwise allowable to Basin (or any successor corporation) for
federal income tax purposes when those options are exercised or the restricted
shares vest or when those severance payments are made will be reduced by the
excess parachute payment triggered by those benefits. In other words, the
deduction to which Basin might otherwise be entitled upon the exercise of those
options (the excess of the fair market value of the purchased shares over the
option exercise price paid for those shares) or the vesting of the restricted
shares (the fair market value of those shares at the time of vesting) will be
reduced by the excess parachute payment attributed to the accelerated vesting of
those stock options or restricted shares, and the deduction otherwise allowable
for the severance payments made to such individual will also be reduced by the
excess parachute payment attributed to those severance benefits. In addition,
the individual would be subject to a 20% excise tax on his excess parachute
payments at the time those payments or benefits are paid or provided.

ACCOUNTING TREATMENT

     The merger will be accounted for as a pooling of interests for accounting
and financial reporting purposes. Under this method of accounting, the recorded
assets and liabilities of Stone and Basin will be carried forward to the
combined company at their recorded amounts, as adjusted to conform significant
accounting policies, and income of the combined company will include income of
Stone and Basin for the entire fiscal year in which the merger occurs. Unaudited
pro forma combined financial statements giving effect to the merger are
presented under "Condensed Unaudited Pro Forma Combined Financial Statements."

     The merger agreement provides that it is a condition to the obligations of
Stone and Basin that certain affiliates of Stone and Basin execute a written
agreement at the effective time of the merger. Pursuant to these agreements,
these affiliates will certify that they have not transferred shares of Stone
common stock or Basin common stock within the preceding 30 days and will not
transfer any shares of Stone common stock or shares of Basin common stock prior
to the date that Stone publishes financial statements that reflect 30 days of
consolidated operations of Stone and Basin. Compliance with these agreements
relates to the ability of Stone to account for the merger as a pooling of
interests.

REGULATORY APPROVALS

     Under the Hart-Scott-Rodino Act, the merger may not be consummated unless
certain filings have been submitted to the Federal Trade Commission and the
Antitrust Division of the U.S. Department of Justice and certain waiting period
requirements have been satisfied. On             , 2000, Stone and Basin
submitted the required filings to the Federal Trade Commission and the Antitrust
Division. The waiting period under the Hart-Scott-Rodino Act terminated on
            , 2000.

     The Federal Trade Commission and the Antitrust Division frequently
scrutinize the legality under the antitrust laws of transactions like the
merger. At any time before or after the completion of the merger, the Federal
Trade Commission or the Antitrust Division could take any action under the
antitrust laws as

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<PAGE>   59

its deems necessary or desirable in the public interest, including seeking to
enjoin the completion of the merger or seeking the divestiture of substantial
assets of Stone or Basin. Stone and Basin believe that the completion of the
merger will not violate the antitrust laws. We cannot predict, however, whether
the merger will be challenged on antitrust grounds, or, if such a challenge is
made, what the result will be.

     Other than as we describe in this document, the merger does not require the
approval of any U.S. federal or state or foreign agency. We will, however, be
required to make various filings with U.S. federal and state and foreign
governmental authorities to complete the merger.

LEGAL PROCEEDINGS

     Basin is, from time to time, a party to litigation arising in the normal
course of its business operations. Based on information currently available,
management of Basin believes that it is not a party to any litigation the
results of which it expects to have a material adverse effect on its business,
financial position or results of operations.

     Stone is, from time to time, a party to litigation arising in the normal
course of its business operations. Based on information currently available,
management of Stone believes that it is not a party to any litigation the
results of which it expects to have a material adverse effect on its business,
financial position or results of operations.

APPRAISAL RIGHTS

     Under Delaware law, a stockholder of a corporation who does not vote in
favor of certain merger transactions and who demands appraisal of such
stockholder's shares in connection therewith may, under varying circumstances,
be entitled to dissenters' rights pursuant to which the stockholder may receive
cash in the amount of the fair value of such stockholder's shares of stock in
lieu of the consideration the stockholder would otherwise receive in the
transaction.

     Unless the corporation's certificate of incorporation provides otherwise,
such dissenters' rights are not available in certain circumstances, including
the merger or consolidation by a corporation the shares of which are either
listed on a national securities exchange or the Nasdaq National Market or are
held of record by more than 2,000 holders if such stockholders receive only
shares of the surviving corporation or shares of any other corporation which are
either listed on a national securities exchange or the Nasdaq National Market or
held of record by more than 2,000 holders, plus cash in lieu of fractional
shares.

     Because Basin's shares of common stock are listed on the Nasdaq National
Market and Basin stockholders will receive, upon consummation of the merger,
only shares of Stone common stock, which will be listed on the NYSE, and cash in
lieu of any fractional shares, Basin common stockholders are not entitled to
dissenters' rights under Delaware law in connection with the merger.

DELISTING AND DEREGISTRATION OF BASIN COMMON STOCK

     If the merger is completed, the shares of Basin common stock will be
delisted from the Nasdaq National Market and will be deregistered under the
Securities Exchange Act of 1934. The stockholders of Basin will become
stockholders of Stone and their rights as stockholders will be governed by
Stone's certificate of incorporation and by-laws and by the laws of the State of
Delaware. See "Comparison of Stockholders' Rights."

FEDERAL SECURITIES LAW CONSEQUENCES

     All shares of Stone common stock that Basin stockholders will receive in
the merger will be freely transferable, except for shares of Stone common stock
that are received by persons who are deemed to be "affiliates" of Basin under
the Securities Act of 1933, as amended, at the time of the Basin special
meeting. These affiliates may resell the shares of Stone common stock they
receive in the merger only in transactions permitted by Rule 145 under the
Securities Act or as otherwise permitted under the Securities Act. Persons who
may be deemed to be affiliates of Basin for the above purposes generally include

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<PAGE>   60

individuals or entities that control, are controlled by or are under common
control with Basin, and include directors and certain executive officers of
Basin. The merger agreement requires that Basin use its reasonable best efforts
to cause each of these affiliates to deliver to Stone, within 30 days of the
date of entering into the merger agreement (and in any event prior to the
effective time), a written agreement to the effect that these persons will not
sell, transfer or otherwise dispose of any of the shares of Stone common stock
issued to them in the merger in violation of the Securities Act or the related
SEC rules.

     This joint proxy statement/prospectus does not cover any resales of the
Stone common stock received in the merger, and no person is authorized to make
any use of this joint proxy statement/prospectus in connection with any such
resales.

U.S. FEDERAL INCOME TAX CONSEQUENCES OF THE MERGER

     The following general discussion summarizes the anticipated material U.S.
federal income tax consequences of the merger to Basin stockholders. This
discussion addresses only those stockholders who hold their shares of Basin
common stock as a capital asset, and does not address all of the U.S. federal
income tax consequences that may be relevant to particular Basin stockholders in
light of their individual circumstances, or to Basin stockholders that are
subject to special rules, such as:

     - financial institutions;

     - mutual funds;

     - tax-exempt organizations;

     - insurance companies;

     - dealers in securities or foreign currencies;

     - traders in securities who elect to apply a mark-to-market method of
       accounting;

     - foreign holders;

     - persons who hold shares of Basin common stock as a hedge against currency
       risk or as part of a straddle, constructive sale or conversion
       transaction; or

     - holders who acquired their shares of Basin common stock upon the exercise
       of employee stock options or otherwise as compensation.

     The following discussion is not binding on the Internal Revenue Service. It
is based upon the Internal Revenue Code of 1986, as amended, and the
regulations, rulings and decisions thereunder in effect as of the date of this
document, all of which are subject to change, possibly with retroactive effect.
Tax consequences under state, local and foreign laws and U.S. federal laws other
than U.S. federal income tax laws, are not addressed. BASIN STOCKHOLDERS ARE
STRONGLY URGED TO CONSULT THEIR TAX ADVISORS AS TO THE SPECIFIC TAX CONSEQUENCES
TO THEM OF THE MERGER, INCLUDING THE APPLICABILITY AND EFFECT OF U.S. FEDERAL,
STATE AND LOCAL AND FOREIGN INCOME AND OTHER TAX LAWS IN THEIR PARTICULAR
CIRCUMSTANCES.

     It is a condition to the closing of the merger that Basin and Stone each
receive an opinion from tax counsel to the effect that the merger will qualify
as a reorganization within the meaning of Section 368(a) of the Internal Revenue
Code. These opinions are based on customary assumptions and customary
representations made by, among others, Basin, Stone and Partner Acquisition
Corp. An opinion of counsel represents counsel's best legal judgment and is not
binding on the Internal Revenue Service or any court. No ruling has been, or
will be, sought from the Internal Revenue Service as to the U.S. federal income
tax consequences of the merger.

     Assuming the merger qualifies as a reorganization within the meaning of
Section 368(a) of the Internal Revenue Code, holders of shares of Basin common
stock that receive shares of Stone common

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<PAGE>   61

stock in the merger will not recognize gain or loss for U.S. federal income tax
purposes, except with respect to cash, if any, they receive in lieu of a
fractional share of Stone common stock. Each stockholder's aggregate tax basis
in the shares of Stone common stock received in the merger will be the same as
such stockholder's aggregate tax basis in the shares of Basin common stock
surrendered in the merger, decreased by the amount of any tax basis allocable to
any fractional share interest for which cash is received. The holding period of
the shares of Stone common stock received in the merger by a holder of shares of
Basin common stock will include the holding period of shares of Basin common
stock that such stockholder surrendered in the merger. A holder of shares of
Basin common stock that receives cash in lieu of a fractional share of Stone
common stock will recognize gain or loss equal to the difference between the
amount of cash received and such stockholder's tax basis in the shares of Basin
common stock allocable to the fractional share. That gain or loss generally will
constitute capital gain or loss. In the case of an individual stockholder, any
of this capital gain generally will be subject to a maximum U.S. federal income
tax rate of 20% if the individual has held his shares of Basin common stock for
more than 12 months on the date of the merger. The deductibility of capital
losses is subject to limitations for both individuals and corporations.

     Because shares of Stone common stock will remain unchanged in the merger,
the merger will not cause Stone stockholders to recognize any gain or loss. No
gain or loss will be recognized by Stone, Basin or Partner Acquisition Corp.

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<PAGE>   62

                              THE MERGER AGREEMENT

     The following is a summary of the material terms of the merger agreement, a
copy of which is attached as Annex A to this document and is incorporated in
this document by reference. This summary is qualified in its entirety by
reference to the merger agreement. You should carefully read the merger
agreement in its entirety because it, and not this document, is the legal
document that governs the merger.

THE MERGER

     At the effective time of the merger, Partner Acquisition Corp., a
newly-formed, wholly-owned subsidiary of Stone, will merge with and into Basin
Exploration, Inc. Basin will be the surviving corporation in the merger and will
become a wholly-owned subsidiary of Stone. The directors and officers of Partner
Acquisition Corp. immediately prior to the effective time of the merger will be
the initial directors and officers of the surviving corporation. At the
effective time, Michael S. Smith, President, Chief Executive Officer and
Chairman of the Board of Basin, will become a member of Stone's board of
directors.

     The closing date of the merger will occur no later than the second business
day following the date on which all conditions to the merger, other than those
conditions that by their nature are to be satisfied at the closing, have been
satisfied or waived, unless we agree on another time. As early as practicable on
the closing date of the merger, we will file a certificate of merger with the
Secretary of State of the State of Delaware. The effective time of the merger
will be the time we file the certificate of merger. We currently anticipate that
we will complete the merger shortly after the Stone and Basin special
stockholders' meetings, assuming our respective stockholders approve at these
meetings the merger, the amendment to Stone's certificate of incorporation and
the issuance of Stone common stock in connection with the merger, and all other
conditions to the merger have been satisfied or waived. Approval by Stone
stockholders of the proposal to amend Stone's certificate of incorporation is a
prerequisite to approval of the proposal for the share issuance by Stone.

MERGER CONSIDERATION

  Exchange Ratio

     As of the effective time of the merger, each issued and outstanding share
of Basin common stock (other than shares of Basin common stock held as treasury
stock and shares that are owned by Stone, Partner Acquisition Corp. or any other
wholly-owned subsidiary of Stone or Basin, which shares will be cancelled and
retired without the right to receive any consideration in exchange therefor)
will be converted into the right to receive .3974 of a share of Stone common
stock. If, between the date of the merger agreement and the effective time of
the merger, the outstanding shares of Basin common stock or Stone common stock
are changed into a different number or class of shares by reason of any stock
split, division or subdivision of shares, stock dividend, reverse stock split,
reclassification, recapitalization or other similar transaction, then the
exchange ratio will be appropriately adjusted to reflect the economic effects
intended by the merger agreement.

  Fractional Shares

     Certificates for fractional shares of Stone common stock will not be issued
in the merger. Basin stockholders who would otherwise receive fractional shares
will instead be entitled to receive a cash payment equal to the value of these
fractional share interests as determined by multiplying the fractional part of a
share of Stone common stock by the average of the last reported sales prices of
Stone common stock on each of the ten trading days immediately preceding the
effective time of the merger.

EXCHANGE PROCEDURES

     As soon as reasonably practicable after the effective time of the merger,
an exchange agent will mail a letter of transmittal to each holder of record of
Basin stock certificates along with instructions for

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<PAGE>   63

effecting the surrender of Basin stock certificates in exchange for certificates
representing shares of Stone common stock (plus cash in lieu of fractional
shares as provided above). This letter of transmittal must be used in
surrendering those stock certificates to the exchange agent for cancellation.
Upon surrender of a Basin stock certificate for cancellation, together with a
duly executed letter of transmittal, the holder of the stock certificate will be
entitled to receive in exchange therefor (1) a Stone certificate representing
the number of whole shares of Stone common stock that the holder has the right
to receive and (2) a check representing the amount of cash payable in lieu of
any fractional shares of Stone common stock, if any. BASIN STOCKHOLDERS SHOULD
NOT SEND IN THEIR STOCK CERTIFICATES UNTIL THEY RECEIVE THE LETTER OF
TRANSMITTAL.

     After the effective time of the merger, each Basin stock certificate, until
surrendered and exchanged, will represent only the right to receive a
certificate representing shares of Stone common stock and cash in lieu of
fractional shares, if any. No interest will be paid or will accrue on any cash
payable to holders of Basin stock certificates. Holders of Basin stock
certificates will not be entitled to receive any dividends or other
distributions with respect to shares of Stone common stock declared or made by
Stone having a record date after the effective time of the merger until the
stock certificates are surrendered. Subject to applicable law, following
surrender of the Basin stock certificates, such dividends and distributions, if
any, will be paid without interest.

REPRESENTATIONS AND WARRANTIES

     The merger agreement contains customary and substantially reciprocal
representations and warranties made by each of us to the other. These
representations and warranties relate to, among other things:

     - corporate organization, qualification and good standing, and ownership of
       subsidiaries;

     - capitalization;

     - corporate power and authority to enter into the merger agreement, and due
       execution, delivery and enforceability of the merger agreement;

     - absence of a breach or violation of charter documents, bylaws, material
       agreements, orders, decrees, permits or laws as a result of the merger;

     - authorizations, consents, approvals and filings required to enter into
       the merger agreement or to complete the transactions contemplated by the
       merger agreement;

     - timely and accurate filings with the SEC in compliance with applicable
       rules and regulations;

     - undisclosed liabilities;

     - absence of certain adverse changes or events;

     - tax matters and actions that would prevent the merger from receiving
       certain tax treatment under the Internal Revenue Code;

     - title to property;

     - intellectual property;

     - material contracts;

     - absence of undisclosed investigations, material litigation and material
       judgments or injunctions;

     - environmental matters;

     - employee benefits and ERISA compliance;

     - compliance with applicable laws and possession of required permits;

     - labor and employee matters (only as to Basin);

     - insurance (only as to Basin);

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<PAGE>   64

     - fairness opinions of financial advisors;

     - state takeover laws (only as to Basin);

     - oil and gas reserve reports and production delivery arrangements;

     - hedging; and

     - required vote of stockholders to approve the merger, the amendment to
       Stone's certificate of incorporation in connection with the merger and
       the issuance of Stone common stock.

     The merger agreement also contains representations and warranties relating
to Partner Acquisition Corp., including: corporate organization, qualification
and good standing; corporate power and authority to enter into the merger
agreement; due execution, delivery and enforceability of the merger agreement;
and non-contravention.

     The representations and warranties contained in the merger agreement will
not survive the merger, but they form the basis of certain conditions to our
obligations to complete the merger. Only certain agreements set forth in the
merger agreement will survive the effective time of the merger.

COVENANTS AND AGREEMENTS

     We have each undertaken several covenants and agreements in the merger
agreement. The following summarizes the more significant of these covenants and
agreements.

  No Solicitation

     Basin has agreed that it will not, nor will it authorize or knowingly
permit, directly or indirectly, any of its officers, directors, employees,
financial advisors, agents and other representatives to:

     - solicit, initiate or encourage any proposals that constitute, or could
       reasonably be expected to lead to, a proposal or offer for a merger,
       consolidation, business combination, share exchange, recapitalization,
       sale of all or substantially all of Basin's assets, sale of shares (other
       than pursuant to Basin's incentive plan or performance share plan) of
       capital stock, including without limitation by way of a tender offer, or
       similar transaction involving us or any of Basin's subsidiaries, other
       than the transactions contemplated by the merger agreement;

     - engage in negotiations regarding, or provide any non-public information
       to any person or entity relating to, or take any other action intended to
       facilitate, any acquisition proposal of the type described above; or

     - agree to or recommend any acquisition proposal of the type described
       above.

     However, prior to the date of Basin's stockholders meeting, Basin is
permitted to:

     - comply with applicable provisions of federal securities laws requiring
       Basin to disclose to its stockholders its position with respect to any
       acquisition proposal; and

     - furnish non-public information to, or enter into negotiations with, any
       person or entity in connection with an unsolicited bona fide written
       acquisition proposal by that person or entity, or recommend an
       unsolicited bona fide written acquisition proposal to Basin's
       stockholders, if and only to the extent that:

      (1) the acquisition proposal was not made by a person or entity with whom
          Basin has actively negotiated an acquisition proposal within the
          three-month period prior to the date of the merger agreement;

      (2) Basin's board of directors, after consultation with its outside legal
          counsel, determines in good faith that such action is legally
          advisable for the board of directors to comply with its fiduciary
          duties to Basin's stockholders under applicable law;

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<PAGE>   65

      (3) the acquisition proposal is not subject to any financing contingencies
          or is, in the good faith judgment of Basin's board of directors, after
          consultation with Basin's financial advisor, reasonably capable of
          being financed by the person or entity making the proposal;

      (4) Basin's board of directors determines in good faith, after
          consultation with Basin's financial advisor, that the acquisition
          proposal is reasonably capable -- taking into account all legal,
          financial, regulatory and other aspects of the proposal and the person
          or entity making the proposal -- of being completed and would, if
          consummated, result in a transaction more favorable to Basin's
          stockholders than the transaction contemplated by the merger
          agreement; and

      (5) prior to furnishing any non-public information to, or entering into
          negotiations with, any person or entity, Basin's board of directors:

         - received from that person or entity an executed confidentiality
           agreement with terms regarding confidentiality and standstill
           provisions no less favorable to us than those contained in the
           confidentiality agreement between Basin and Stone; and

         - notified Stone of the acquisition proposal, including the material
           terms and conditions of the proposal and the identity of the person
           or entity making the proposal.

  Stockholders Meetings

     We have each agreed to call a meeting of our respective stockholders to be
held as promptly as practicable. At the meeting of Basin's stockholders, Basin
will submit the merger agreement and the merger for approval. At the meeting of
Stone's stockholders, Stone will submit an amendment to its certificate of
incorporation to increase its authorized capitalization and the issuance of its
shares of common stock in connection with the merger for approval. Approval of
the proposal to amend Stone's certificate of incorporation is a prerequisite to
approval of the proposal for the share issuance. We have also agreed to
coordinate and cooperate with respect to the timing of our respective meetings,
and to use our reasonable best efforts to hold the meetings on the same day.
Except as otherwise permitted with respect to Basin under the circumstances
described above under "-- No Solicitation," each of us shall use our reasonable
best efforts to solicit proxies in favor of the matters described above to be
voted upon by our respective stockholders and obtain a sufficient vote in favor
of such matters at our respective stockholder meetings. Stone has also agreed to
take such action with respect to Partner Acquisition Corp., and to cause Partner
Acquisition Corp. to take such action, as may be required to consummate the
merger, including without limitation, voting all shares of Partner Acquisition
Corp. in favor of the merger.

  Board of Directors Covenant to Recommend

     We have each agreed that this joint proxy statement/prospectus would
include the recommendation of Basin's board of directors in favor of the merger
agreement and the merger and of Stone's board of directors in favor of the
amendment to Stone's certificate of incorporation and the issuance of shares of
Stone's common stock in connection with the merger. However, Basin's board of
directors is permitted to withdraw its recommendation under the circumstances
described above under "-- No Solicitation," and we are each permitted to make
factual disclosures to our respective stockholders to the extent required to do
so by applicable law. Basin's obligation to call and hold a stockholders meeting
is not dependent on its board of directors' recommendation.

  Operations of the Companies Pending Closing

     We have each undertaken a separate covenant that places restrictions on
ourselves and our respective subsidiaries until the earlier of the effective
time of the merger or the termination of the merger agreement. In general, we
and our respective subsidiaries are required to carry on our operations in the
usual, regular and ordinary course of business in substantially the same manner
as previously conducted

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<PAGE>   66

and, to the extent consistent with such business, to use all reasonable efforts
consistent with past practices and policies to preserve intact our present
business.

     We have each also agreed to limitations, prohibitions and other provisions
relating to the conduct of our respective businesses during the period from the
date of the merger agreement to the earlier of the effective time of the merger
or the termination of merger agreement with respect to:

     - declaring or paying any dividends on or distributions in respect of our
       respective capital stock;

     - splits, combinations or reclassifications of our capital stock or the
       issuance or authorization of issuance of any other securities in respect
       of, in lieu of or in substitution for shares of our capital
       stock -- except that Stone is entitled to effect a stock split so long as
       an appropriate adjustment is made to the exchange ratio;

     - amendments or proposals to amend our respective certificates of
       incorporation or bylaws, except as contemplated by the merger agreement;

     - the adoption of a plan of complete or partial liquidation, dissolution or
       reorganization; and

     - changes in any method of accounting or accounting practice with respect
       to us or our respective subsidiaries, except for any changes required by
       generally accepted accounting principles.

     Basin has agreed to additional limitations, prohibitions and other
provisions relating to the conduct of its business and the business of its
subsidiaries with respect to:

     - accelerating, amending or changing the period of exercisability of
       options, restricted stock or other awards granted under any employee
       stock plan, including Basin's incentive plan and performance share plan,
       or authorizing cash payments in exchange for any options granted under
       any of such plans except as required by the terms of such plans or
       certain employment agreements or other related agreements in effect as of
       the date of the merger agreement;

     - purchasing or otherwise acquiring, directly or indirectly, any shares of
       Basin's capital stock, except from former employees, directors and
       consultants in accordance with agreements providing for the repurchase of
       shares in connection with any termination of service to those parties;

     - issuing, delivering or selling, or authorizing or proposing the issuance,
       delivery or sale, of any shares of Basin's capital stock or securities
       convertible into shares of Basin's capital stock, or subscriptions,
       rights, warrants or options to acquire, or other agreements or
       commitments of any character obligating Basin or its subsidiaries to
       issue any such shares or other convertible securities, other than (1) the
       issuance of shares of Basin's common stock pursuant to the exercise of
       options outstanding on the date of the merger agreement in accordance
       with their current terms, or (2) the issuance, earning or vesting of
       shares of Basin's common stock pursuant to outstanding performance share
       awards under Basin's performance share plan or other similar awards,
       including restricted stock awards under Basin's incentive plan, made
       prior to the date of the merger agreement, in accordance with their
       current terms;

     - acquiring or agreeing to acquire by merging or consolidating with, or by
       purchasing a substantial equity interest in or substantial portion of the
       assets of, or by any other manner, any business or any corporation,
       partnership or other business organization or division, except as
       described in the merger agreement;

     - except (1) in accordance with Basin's employee retention policy, (2)
       pursuant to the current terms of certain of Basin's existing contracts,
       obligations or agreements, (3) in connection with the payment of
       non-discretionary contributions to Basin's 401(k) plan at a designated
       level and (4) the payment of year-end bonuses up to a designated cap:

      -- increasing or agreeing to increase the compensation payable or to
         become payable to employees or officers;

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<PAGE>   67

      -- granting any additional severance or termination pay to, or entering
         into any employment or severance agreements with, any employees or
         officers;

      -- entering into any collective bargaining agreement, other than as
         required by law or extensions to existing agreements in the ordinary
         course of business;

      -- amending any of Basin's employee plans, other than certain specified
         amendments, or establishing, adopting, entering into or amending any
         bonus, profit sharing, thrift, compensation, stock option, restricted
         stock, pension, retirement, deferred compensation, employment,
         termination, severance or other plan, trust, fund, policy or
         arrangement for the benefit of any directors, officers or employees,
         except to the extent required by applicable law; and

      -- paying any material benefit or amount not required by a plan or
         arrangement as in effect on the date of the merger agreement to any
         person;

     - incurring, assuming, guaranteeing or prepaying any indebtedness for
       borrowed money, other than under Basin's existing credit facility in the
       ordinary course of business;

     - modifying or terminating any of Basin's material contracts or waiving or
       relinquishing any right under any of Basin's material contracts, other
       than any amendment to Basin's credit facility to reflect a
       redetermination of Basin's borrowing base under the facility and other
       than any modification, termination, waiver or relinquishment that is not
       adverse to Basin;

     - entering into any hedges or fixed price commodity sales agreements,
       except as may be agreed to by Stone;

     - making any material tax elections or settlements or compromises of any
       material tax liability;

     - except as permitted by the merger agreement:

      -- making any material capital expenditure, except as may be required to
         (1) continue operations on the drilling, completion or plugging of any
         well or any well operation for which Basin has consented to participate
         and is required to continue to participate pursuant to applicable
         agreements or (2) conduct emergency operations on any well, platform,
         pipeline or other production facility;

      -- entering into any sale, lease, farm-out or similar disposition (except
         for the sale of hydrocarbons or personal property in the ordinary
         course of business) of any (1) proved reserves described in Basin's
         reserve report or (2) interests in other properties without first
         granting Stone an option, to be exercised by Stone within 5 days, to
         acquire the interests on the same terms as they are being offered to a
         third party or industry provided, Basin has the right to relinquish
         interests in such properties pursuant to elections not to participate
         in operations proposed by third parties under operating or other
         applicable agreements so long as, to the extent allowed under such
         agreements, Basin has promptly offered Stone the opportunity to
         participate for, and thereby acquire, Basin's interest in such
         operation and Stone has either affirmatively rejected such options or
         failed to timely respond, provided further, that Basin shall not enter
         into any sale, lease, farmout, or other alienation or disposition of
         any interest in certain designated prospects;

      -- entering into any material joint venture agreement, partnership
         agreement or similar agreement not in conjunction with acquisitions or
         capital expenditures contemplated in the merger agreement or otherwise
         disclosed;

      -- acquiring or agreeing to acquire any assets other than inventory,
         equipment and other similar items in the ordinary course of business;
         and

      -- entering into any transaction with any third party in which, to Basin's
         knowledge, any officer or director of Basin has, directly or
         indirectly, any existing or prospective equity or other ownership
         interest or any other arrangement or understanding having the same
         economic effect, other than with respect to small holdings in publicly
         traded companies;

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<PAGE>   68

     -- waiving, releasing, assigning, or settling any material rights, claims
        or pending or threatened litigation matters; and

     -- entering into any contract, agreement, arrangement or understanding that
        materially limits or otherwise materially restricts Basin or any of its
        subsidiaries or any successor thereto, or that would, after the
        effective time of the merger, limit or restrict the surviving
        corporation and its affiliates (including Stone) or any successor
        thereto, from engaging in or competing in any line of business or in any
        geographic area, except for confidentiality agreements relating to
        specific prospects.

     Stone has agreed to additional limitations with respect to the issuance of
its common stock in connection with any acquisition of equity interests or
assets that could reasonably be expected to adversely affect Stone's ability to
consummate the merger or that would reasonably be expected to otherwise delay
the merger.

  Employee Benefit Matters

     If requested by Stone, Basin will be required to take all action necessary
to terminate before the effective time of the merger Basin's 401(k) plan. Stone
will provide the opportunity for participants in Basin's 401(k) plan who are
employed by Basin or Stone on the date that is 60 days after the closing date of
the merger to "roll over" their account balances into Stone's 401(k) plan.

     At the effective time of the merger or following a reasonable transition
period, Basin's continuing employees will be eligible to participate in those
Stone employee plans maintained for similarly situated employees of Stone, or in
substantially similar programs. The continuing employees will be eligible to
participate on the same terms applicable to similarly situated employees of
Stone and to the extent that Stone's plans and programs provide benefits for:

     - medical, dental and vision care,

     - life insurance,

     - disability income,

     - sick pay,

     - holiday and vacation pay,

     - 401(k) plan coverage,

     - Internal Revenue Code Section 125 benefit arrangements,

     - bonus, profit-sharing or other incentive plans,

     - pension or retirement programs,

     - dependent care assistance,

     - severance benefits, and

     - employee stock option and stock purchase plans.

     Each continuing employee will be given credit, in the circumstances set
forth in the merger agreement, for accrued vacation and sick leave time, for his
or her period of service with Basin, and for payments pursuant to co-payment,
deductible or other co-insurance features. Each continuing employee and eligible
dependent who, at the effective time of the merger (or, if later, the time of
the transition of the employee from a Basin employee plan to a Stone employee
plan), was participating in an employee group health plan maintained by Basin
will not be excluded from Stone's employee group health plan or limited in
coverage under that plan by reason of any waiting period restriction or
pre-existing condition limitation to the extent such restriction or limitation
did not apply to the continuing employee as of the

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<PAGE>   69

effective time of the merger (of, if later, the time of transition of the
employee from a Basin employee plan to a Stone employee plan) under Basin's
group health plan.

     Stone will make all payments to be paid after the effective time of the
merger pursuant to the provisions contained in Basin's retention policy and will
recognize all vesting, acceleration and other provisions under all written
agreements containing change in control type provisions applicable to Basin's
officers, employees or directors in existence as of the date of the merger
agreement and disclosed to Stone.

     To the extent permitted by, and in the manner described in, the merger
agreement, Basin may facilitate the elimination of loss of deductions and excise
taxes under Sections 280G and 4999 of the Internal Revenue Code with respect to
severance payments and other benefits to be provided to those persons who are
party to certain disclosed agreements by making specified advances to such
persons.

     Basin agreed that the following employee benefit payments shall not exceed
designated amounts: (1) annual bonuses that are paid or payable to Basin
employees for calendar year 2000; (2) retention and severance benefits to be
paid or payable to employees of Basin and its subsidiaries under Basin's
retention and severance policy; and (3) cash severance payments to be paid or
payable to employees of Basin and its subsidiaries (exclusive of any severance
payments attributable to the accelerated vesting of options or restricted stock
or performance share awards) pursuant to certain disclosed agreements.

     Until the closing of the merger, Basin is permitted to approve and assign
overriding royalty interests to its geoscientists pursuant to its existing
Onshore Geoscientist Overriding Royalty Interest Plan and Gulf Coast
Geoscientist Overriding Royalty Interest Plan, as more particularly described in
the merger agreement.

  Treatment of Basin Stock Options and Plans

     Assumption of Incentive Plan and Options.  At the effective time of the
merger, Stone will assume each option outstanding at such time to purchase
shares of Basin common stock under Basin's incentive plan, whether vested or
unvested (after giving effect to any applicable change in control or similar
type provisions), and Stone will assume Basin's incentive plan.

     Basin Options.  Each assumed Basin option will be converted into an option
to acquire, on the same terms and conditions in effect for the option
immediately prior to the closing date of the merger, that number of shares of
Stone common stock determined by multiplying the number of shares of Basin
common stock subject to that option immediately prior to the closing date of the
merger by .3974 and rounding out to the next whole number of shares. The
exercise price per share of Stone common stock subject to each assumed option
will be equal to the amount determined by dividing the exercise price per share
of Basin common stock in effect for that option immediately prior to the closing
date of the merger by .3974 and rounding up to the nearest whole cent.

     Form S-8.  Within 30 days after the effective time of the merger, Stone
will file a registration statement on Form S-8 or other appropriate form with
the SEC to register Stone common stock issuable upon exercise of the assumed
Basin options and will use its commercially reasonable best efforts to cause the
registration statement to remain effective, and to maintain the current status
of the prospectus or prospectuses contained therein, until the exercise or
expiration of the options.

     Basin's Performance Share Plan.  At the effective time of the merger, the
shares of Basin's common stock subject to earn-out schedules pursuant to the
outstanding performance share awards under Basin's performance share plan will
be earned or forfeited by the holders thereof in accordance with the change in
control provisions of such holders' share awards. Any shares not earned based on
the most recently issued year-end financial statement prior to the effective
time of the merger will be earned as determined prior to the effective time by
the compensation and incentive committee of Basin's board of directors under
Basin's performance share plan (and subject to the prior approval of Stone)
based on Basin's financial performance during the period beginning on the first
day of the fiscal year in which the effective time of the merger occurs and
ending on the closing date of the merger. The earned shares will, at the
effective

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time of the merger, be converted into shares of Stone common stock in accordance
with the exchange ratio.

     Approvals.  Prior to or as of the effective time of the merger, the board
of directors of Basin will take appropriate action to approve the deemed
cancellation of the Basin stock options for purposes of Section 16(b) of the
Exchange Act, and the board of directors of Stone will take appropriate action
to approve the deemed grant of options to purchase shares of Stone common stock
under the Basin stock options (as converted into options to purchase shares of
Stone common stock at the effective time of the merger) for purposes of Section
16(b) of the Exchange Act. The disposition of such shares of Basin common stock
and the issuance of such shares of Stone common stock in the merger will also be
included in the approval process of the boards of directors of Basin and Stone
for purposes of Section 16(b) of the Exchange Act. Similar action will be taken
by the boards of directors of Basin and Stone with respect to the shares of
Basin common stock outstanding under Basin's performance share plan that are to
be converted into shares of Stone common stock in the Merger.

     Restricted Stock.  If any shares of Basin common stock are, immediately
prior to the effective time of the merger, unvested or subject to any other
restrictions under Basin's incentive plan or any restricted stock purchase or
stock issuance agreement to which Basin is a party and the vesting schedule or
restrictions applicable to those shares are not to vest or lapse on an
accelerated basis in connection with the merger, then the shares of Stone common
stock issued in exchange for those shares of Basin common stock in the merger
will also be unvested and subject to the same vesting schedule in effect for the
unvested shares of Basin common stock immediately prior to the effective time of
the merger.

  Other Covenants

     Cooperation.  We have each agreed to confer on a regular and frequent
basis, from the date of the merger agreement until the effective time of the
merger, with each other's representatives to report on the general status of
ongoing operations, subject to compliance with applicable law. Each of us also
agreed to promptly provide the other party or its counsel with copies of all
filings made by each of us with any governmental entity in connection with the
merger agreement, the merger and the transactions contemplated by the merger
agreement and the merger. We further agreed to work in good faith and use our
reasonable best efforts to satisfy all of the closing conditions described in
the merger agreement.

     Access to Information.  We have each agreed to afford one another and one
another's representatives reasonable access for purposes reasonably related to
the merger agreement and the consummation of the transactions contemplated by
the merger agreement, during normal business hours, to all of our, and our
respective subsidiaries', properties, books, contracts, commitments and records.
Each inspecting party must agree to be bound by the terms of the existing
confidentiality agreement between Basin and Stone, or otherwise agree to treat
any information provided as confidential. We have also agreed to furnish, or
cause our respective subsidiaries to furnish, promptly to the other a copy of
each document filed or received prior to the effective time of the merger
pursuant to federal securities laws, and all other information concerning each
other's businesses, properties and personnel as the other party may reasonably
request for purposes reasonably related to the merger agreement and the
consummation of the transactions contemplated by the merger agreement. We have
each agreed to hold any information that is nonpublic in confidence in
accordance with our confidentiality agreement, unless we are otherwise required
by law to disclose the information.

     Affiliate Agreements.  Basin agreed to deliver to Stone, upon the execution
of the merger agreement, a list of all persons who are, in Basin's reasonable
judgment, Basin's "affiliates" for purposes of Rule 145 under the Securities
Act. Basin agreed to use its reasonable best efforts to cause each person who is
identified as an affiliate to execute and deliver to Stone an affiliate
agreement prior to the effective time of the merger. In each affiliate
agreement, each of Basin's affiliates will agree to comply with the applicable
requirements of Rule 145 and those other requirements as may be necessary for
the merger to be treated as a pooling of interests for accounting purposes.

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     Filings; Other Action.  We have each agreed to use our reasonable best
efforts to:

     - take, or cause to be taken, all appropriate action, and do, or cause to
       be done, all things necessary and proper under applicable law to
       consummate and make effective the transactions contemplated by the merger
       agreement as promptly as practicable;

     - obtain from any governmental entity or any other third party any
       consents, licenses, permits, waivers, approvals, authorizations, or
       orders required to be obtained or made in connection with the
       authorization, execution and delivery of the merger agreement and the
       consummation of the transactions contemplated by the merger agreement;
       and

     - as promptly as practicable, make all necessary filings, and thereafter
       make any other required submissions, with respect to the merger agreement
       and the merger required under (1) the Securities Act and the Exchange
       Act, and any other applicable federal or state securities laws, (2) the
       Hart-Scott-Rodino Antitrust Improvements Act and any related governmental
       request under that act and (3) any other applicable law.

     We have agreed to cooperate with each other in connection with the making
of all filings and to use our reasonable best efforts to furnish to each other
all information required for any application or other filing to be made pursuant
to the rules and regulations of any applicable law in connection with the
transactions contemplated by the merger agreement.

     We have each agreed to cooperate, cause each of our respective subsidiaries
to cooperate, and to use our respective reasonable best efforts to (1) obtain
any government clearances required for the closing of the merger, (2) respond to
any government requests for information, and (3) contest and resist any action,
including any legislative, administrative or judicial action, and to have
vacated, lifted, reversed or overturned any decree, judgment, injunction or
other order (whether temporary, preliminary or permanent) that restricts,
prevents or prohibits the consummation of the merger or the transaction
contemplated by the merger agreement. However, neither of us is required, in
connection with the receipt of any regulatory approval, to proffer to or agree
to sell or hold separate and agree to sell, divest or to discontinue or limit
any of our, or our respective affiliates', assets, businesses, or interest in
any assets or businesses, or to any conditions relating to, or changes or
restrictions in, the operations of any of our assets or businesses, which, in
either case, could reasonably be expected to have a material adverse effect on
Basin or on Stone, as applicable, or to materially and adversely impact the
economic or business benefits to either party of the transactions contemplated
by the merger agreement.

     Tax-Free Reorganization.  We have agreed to use our reasonable best efforts
to cause the merger to be treated as a reorganization within the meaning of
Section 368(a) of the Internal Revenue Code. We have also agreed that we will
not knowingly take any actions that could prevent the merger from being so
treated.

     New York Stock Exchange Listing.  Stone has agreed to use its reasonable
best efforts to cause the shares of its common stock to be issued in the merger
to be approved for listing on the New York Stock Exchange, subject to official
notice of issuance, prior to the closing date of the merger.

     Indemnification and Insurance.  Stone has agreed that, from and after the
effective time of the merger, it will, and it will cause the surviving
corporation to, indemnify and hold harmless each of Basin's present and former
directors and officers against any costs or expenses, judgments, fines, losses,
claims, damages, liabilities or amounts paid in settlement incurred in
connection with any claim, action, suit, proceeding or investigation, whether
civil, criminal, administrative or investigative, arising out of or pertaining
to matters existing or occurring at or prior to the effective time of the
merger, whether asserted or claimed prior to, at or after the effective time of
the merger, to the fullest extent that Basin would have been permitted under law
and its certificate of incorporation or bylaws in effect on the date of the
merger agreement to indemnify such parties.

     Stone also agreed, for six years from the effective time of the merger, to
cause the surviving corporation to maintain in effect a directors' and officers'
liability insurance policy covering those persons

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who were covered by Basin's directors' and officers' liability insurance policy
as of the date of the merger agreement, with coverage in amount and scope at
least as favorable as Basin's existing coverage, except that Stone is not
required to spend beyond a specified amount for annual premiums.

     Public Disclosure.  We each agreed that we will not issue any press release
or make any public statement with respect to the merger or the merger agreement
prior to consulting with the other party and obtaining the express prior written
approval of the other party, except as may be required by law and any applicable
stock exchange rules. We also agreed that prior to the effective time of the
merger or the termination of the merger agreement, we would endeavor to provide
the other party with a copy of any other press release by the close of business
on the business day prior to the issuance of the press release or, if that
notice is impracticable to provide, as soon as practicable prior to the release.

     Pooling Accounting.  From and after the date of the merger agreement and
until the effective time of the merger, neither of us, nor any of our respective
subsidiaries, may knowingly take any action, or knowingly fail to take any
action, that would jeopardize the treatment of the merger as a pooling of
interests for accounting purposes.

     Brokers or Finders.  Other than as to each party's payment of the fees of
its financial advisor, we have agreed to indemnify each other from claims,
liabilities or obligations for broker's and finder's fees, commissions or
expenses asserted by any person on the basis of any act or statement alleged to
have been made by the indemnifying party or any of its affiliates.

CONDITIONS

  Mutual Conditions

     Our respective obligations to complete the merger are subject to the
satisfaction of the following conditions:

     - the merger agreement and the merger have been approved and adopted by
       Basin's stockholders and the amendment to Stone's certificate of
       incorporation to increase the authorized shares of Stone common stock and
       the issuance of Stone common stock issuable in the merger have been
       approved by Stone's stockholders;

     - the SEC has declared the registration statement effective under the
       Securities Act, and the registration statement is not subject to any stop
       order or proceedings seeking a stop order;

     - the shares of Stone common stock to be issued in the merger have been
       approved for listing on the New York Stock Exchange;

     - any applicable waiting period under the Hart-Scott-Rodino Antitrust
       Improvements Act relating to the merger has expired or been terminated;

     - all authorizations, consents, orders or approvals of, or declarations or
       filings with, or expirations of waiting periods imposed by, any
       governmental authority have been filed, obtained or occurred, except in
       those cases where no material adverse effect would result; and

     - no governmental entity or federal, state or foreign court of competent
       jurisdiction has enacted, issued, promulgated, enforced or entered any
       order or statute, rule or regulation that is in effect and that has the
       effect of making the merger illegal or otherwise prohibiting the
       consummation of the merger.

  Conditions to Obligations of Stone and Partner Acquisition Corp. to Complete
the Merger

     The conditions to Stone's and Partner Acquisition Corp.'s obligations to
complete the merger also include the following:

     - the representations and warranties of Basin in the merger agreement,
       disregarding any materiality or material adverse effect qualifications
       set forth therein, are true and correct as of the date of the

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       merger agreement (except to the extent such representations and
       warranties speak as of an earlier date) and as of the closing date as
       though made on and as of the closing date, except for changes
       contemplated by the merger agreement and where the failures to be true
       and correct, individually or in the aggregate, do not have a material
       adverse effect on Basin or a material adverse effect upon the
       consummation of the transactions contemplated hereby;

     - Basin has performed in all material respects all of its obligations
       required to be performed by it under the merger agreement;

     - Stone has received an opinion of tax counsel to the effect that the
       merger will be treated for federal income tax purposes as a tax-free
       reorganization within the meaning of Section 368(a) of the Internal
       Revenue Code; and

     - except as otherwise provided by the merger agreement, Stone has received
       a letter from Arthur Andersen LLP to the effect that Basin is a "poolable
       entity" and the merger, for financial accounting purposes, is a pooling
       of interests.

  Conditions to Basin's Obligations to Complete the Merger

     The conditions to Basin's obligations to complete the merger also include
the following:

     - the representations and warranties of Stone and Partner Acquisition Corp.
       in the merger agreement, disregarding any materiality or material adverse
       effect qualifications set forth therein, are true and correct as of the
       date of the merger agreement (except to the extent such representations
       and warranties speak as of an earlier date) and as of the closing date as
       though made on and as of the closing date, except for changes
       contemplated by the merger agreement and where the failures to be true
       and correct, individually or in the aggregate, do not have a material
       adverse effect on Stone or a material adverse effect upon the
       consummation of the transactions contemplated hereby;

     - each of Stone and Partner Acquisition Corp. has performed in all material
       respects all obligations required to be performed by them under the
       merger agreement;

     - Basin has received an opinion of tax counsel to the effect that the
       merger will be treated for federal income tax purposes as a tax-free
       reorganization within the meaning of Section 368(a) of the Internal
       Revenue Code; and

     - except as otherwise provided by the merger agreement, Basin has received
       a letter from Arthur Andersen LLP to the effect that Basin is a "poolable
       entity" and the merger, for financial accounting purposes, is a pooling
       of interests.

TERMINATION

     The merger agreement may be terminated at any time before the effective
time of merger, whether before or after approval of the matters presented in
connection with the merger by our respective stockholders:

     - if both of us agree to terminate the merger agreement by mutual written
       consent;

     - by either of us if the merger has not been completed by May 31, 2001,
       except that the right to terminate the merger agreement under this
       provision is not available to any party whose failure to fulfill any of
       its obligations under the merger agreement was the cause of or resulted
       in the failure of the merger to occur on or before May 31, 2001;

     - by either of us if a court of competent jurisdiction or other
       governmental entity has issued a non-appealable final order, decree or
       ruling or taken any other non-appealable final action, in each case
       having the effect of permanently enjoining or otherwise permanently
       prohibiting the merger;

     - by either of us if, at Basin's stockholders' meeting, Basin does not
       obtain the requisite vote of its stockholders in favor of the merger
       agreement and the merger, or if, at Stone's stockholders'

                                       65
<PAGE>   74

       meeting, the required vote for the approval of the amendment to Stone's
       certificate of incorporation and the issuance of Stone common stock in
       the merger is not obtained;

     - by Stone, if (1) Basin's board of directors has withdrawn or modified, in
       a manner adverse to Stone, its recommendation of the merger agreement or
       the merger, (2) Basin's board of directors has recommended to Basin's
       stockholders an acquisition proposal that is more favorable than Stone's
       acquisition proposal, or (3) a tender offer or exchange offer for more
       than 35% of the outstanding shares of Basin's capital stock is commenced
       and Basin's board of directors recommends in favor of the acceptance of
       such offer;

     - by Basin, if Stone's board of directors has withdrawn or modified, in a
       manner adverse to Basin, its recommendation of the amendment to Stone's
       certificate of incorporation to increase its authorized shares of common
       stock or the issuance of Stone common stock in the merger; or

     - by either of us if, there has been a breach of any representation,
       warranty, covenant or agreement on the part of the other party set forth
       in the merger agreement, which breach (1) would, if uncured at closing,
       cause the closing conditions relating to our respective representations
       and warranties and performance of our respective obligations not to be
       satisfied, and (2) the breach is not cured within 20 business days after
       written notice of the breach is received from the other party.

EFFECT OF TERMINATION

     In the event of a termination of the merger agreement as provided above,
the merger agreement will immediately become void, except for certain provisions
relating to brokers fees, nonsurvival of representations, warranties and
agreements, governing law, assignment, termination fees and the payment of costs
and expenses and other specifically identified miscellaneous provisions. In
addition, in the event of a termination of the merger agreement, the
confidentiality agreement between us and Stone will survive and remain in full
force and effect. Except for certain provisions relating to payment of brokers
fees, termination fees and other costs and expenses, there will be no liability
or obligation on the part of Basin, Stone, Partner Acquisition Corp. or our
respective officers, directors, stockholders or affiliates; except that nothing
in the merger agreement relieves any party from liability for the willful and
knowing material breach of any of its representations, warranties, covenants or
agreements set forth in the merger agreement.

TERMINATION FEES

  Termination Fees Payable by Basin

     Basin has agreed to pay Stone a termination fee of $15 million upon the
earliest to occur of the following events:

     - Basin consummates, or executes a definitive agreement providing for, a
       merger, consolidation, business combination, share exchange,
       recapitalization, sale of all or substantially all of Basin's assets,
       sale of shares of Basin's capital stock (with certain exceptions) or
       similar transaction involving Basin or any of its subsidiaries, other
       than the merger with Stone, within 12 months after the termination of the
       merger agreement by either Stone or Basin based on the failure of the
       merger to be consummated by May 31, 2001 or the failure to obtain Basin
       stockholder approval of the merger, if an alternative acquisition
       proposal has been publicly announced and not subsequently abandoned or
       withdrawn prior to (1) the date of termination, in the event of
       termination based on the failure to consummate the merger by May 31,
       2001, or (2) the date of Basin's stockholders' meeting, in the event of
       termination based on the failure to obtain Basin stockholder approval of
       the merger; or

     - Stone terminates the merger agreement based on:

        -- Basin's board of directors withdrawal or modification, in a manner
           adverse to Stone, of its recommendation of the merger agreement or
           the merger;

                                       66
<PAGE>   75

        -- Basin's board of directors recommendation to its stockholders of an
           acquisition proposal that is more favorable than Stone's acquisition
           proposal; or

        -- the commencement of a tender offer or exchange offer for more than
           35% of the outstanding shares of Basin's capital stock and Basin's
           board of directors recommends in favor of the acceptance of such
           offer.

  Termination Fees Payable by Stone

     Stone has agreed to pay Basin a termination fee of $15 million if the
merger agreement is terminated by Basin or Stone based on:

     - the failure of the merger to be consummated by May 31, 2001; or

     - the failure of Stone to obtain Stone stockholder approval of the
       amendment to Stone's certificate of incorporation to increase the
       authorized shares of Stone common stock and the issuance of Stone shares
       in the merger,

if (1) any proposal or offer from a third party involving the acquisition of
Stone, whether in the form of a tender offer for, or merger or other business
combination with, Stone has been publicly announced and not subsequently
abandoned or withdrawn prior to the date of termination, in the event of
termination based on the failure of the merger to be consummated by May 31,
2001, or the date of Stone's stockholders' meeting, in the event of termination
based on the failure to obtain Stone stockholder approval of the amendment to
Stone's certificate of incorporation to increase the authorized shares of Stone
common stock and the issuance of Stone shares in the merger; and (2) the
proposal or offer is consummated, or Stone executes a definitive agreement
providing for the proposal or offer, within 12 months after such termination.

COSTS AND EXPENSES

     Except for the termination fees described above, all fees and expenses
incurred in connection with the merger agreement will be paid by the party
incurring the expenses, whether or not the merger is consummated, except that
the filing fee in connection with any Hart-Scott-Rodino antitrust filing, and
the expenses incurred in connection with the filing, printing and mailing of
this joint proxy statement are shared equally by Basin and Stone.

AMENDMENT AND WAIVER

     We may amend the merger agreement in writing, by action taken or authorized
by our respective boards of directors, at any time before or after approval of
the matters presented in connection with the merger by our respective
stockholders, but, after that approval, we may not make any amendment that by
law requires further approval by our stockholders without that further approval.
At any time before the effective time of the merger, we may, by action taken or
authorized by our respective boards of directors, to the extent legally allowed:

     - extend the time for the performance of any obligations or other acts of
       the other;

     - waive any inaccuracies in the representations and warranties of the other
       contained in the merger agreement or in any document delivered pursuant
       to the merger agreement; and

     - waive compliance with any of the agreements or conditions of the other
       contained in the merger agreement.

                                       67
<PAGE>   76

                               VOTING AGREEMENTS

     The following summary of the Basin voting agreement and the Stone voting
agreement is qualified in its entirety by reference to the complete text of the
Basin voting agreement and the Stone voting agreement, each of which is
incorporated by reference and attached as an exhibit to Annex A to this joint
proxy statement/prospectus. We urge you to read the full text of these voting
agreements.

BASIN VOTING AGREEMENT

     In connection with the execution and delivery of the merger agreement,
Stone entered into the Basin voting agreement with the existing directors of
Basin, solely in their capacity as stockholders, under which these stockholders
agreed to vote their shares of Basin common stock in favor of the adoption of
the merger agreement and approval of the transactions contemplated thereby,
including the merger. As of the record date for the special meeting, these
stockholders owned shares of Basin common stock representing approximately   %
of the total voting power of the outstanding Basin common stock. Approval of the
merger agreement and the transactions contemplated by the merger agreement,
including the merger, requires the approval of the holders of a majority of the
outstanding shares of Basin common stock.

     These Basin stockholders also agreed not to solicit, initiate or encourage
the submission of any proposal or offer for a merger, consolidation, business
combination, share exchange, recapitalization, sale of all or substantially all
of Basin's assets or similar transactions involving Basin or any of its
subsidiaries or participate in any negotiations regarding, or furnish to any
person any information with respect to, or take any other action to facilitate
any inquiries or the making of any proposal that constitutes or may reasonably
be expected to lead to any of the above, or agree to or recommend any of the
above, except as would be permitted by Basin under the merger agreement. The
Basin voting agreement prohibits, subject to limited exceptions, any stockholder
from selling, transferring, pledging, assigning or otherwise disposing of any
shares of Basin common stock. The Basin voting agreement terminates upon the
earlier to occur of the completion of the merger and the termination of the
merger agreement in accordance with its terms.

STONE VOTING AGREEMENT

     In connection with the execution and delivery of the merger agreement,
Basin entered into the Stone voting agreement with the existing directors of
Stone, solely in their capacity as stockholders, under which these stockholders
agreed to vote their shares of Stone common stock in favor of the amendment to
Stone's certificate of incorporation to increase the authorized shares of Stone
common stock and the issuance of shares of Stone common stock in connection with
the merger. As of the record date for the special meeting, these stockholders
owned shares of Stone common stock representing approximately   % of the total
voting power of the outstanding Stone common stock. Approval of the amendment to
Stone's certificate of incorporation to increase the authorized shares of
Stone's common stock requires the approval of the holders of a majority of all
outstanding shares of Stone common stock. Approval of the share issuance
requires the approval of the holders of a majority of the votes cast on the
proposal, provided that the total votes cast on the proposal represent over 50%
in interest of all securities entitled to vote on the proposal.

     These Stone stockholders agreed not to solicit, initiate or encourage the
submission of any acquisition proposal for Stone or participate in any
discussions or negotiations regarding, or furnish to any person any information
with respect to, or take any other action to facilitate any inquiries or the
making of any proposal that constitutes or may reasonably be expected to lead to
any takeover proposal for Stone. The Stone voting agreement prohibits, subject
to limited exceptions, any stockholder from selling, transferring, pledging,
assigning or otherwise disposing of any shares of Stone common stock. The Stone
voting agreement terminates upon the earlier to occur of the completion of the
merger and the termination of the merger agreement in accordance with its terms.

                                       68
<PAGE>   77

                                 THE COMPANIES

BUSINESS OF BASIN EXPLORATION, INC.

     Basin is an independent oil and gas company engaged in the exploration,
development and acquisition of oil and gas properties located in the shallow
waters of the Gulf of Mexico and selected areas of the onshore United States,
including the Powder River and Green River Basins of Wyoming. In 1996, Basin
sold its property in the Denver-Julesberg Basin, which represented approximately
70% of its fixed assets at the time, in order to commence an active exploratory
drilling program in the Gulf of Mexico. Since that time, Basin has significantly
increased its proved reserves, production and operating cash flow, primarily
through its Gulf of Mexico drilling operations. As of December 31, 1999, Basin
had estimated proved reserves of approximately 134.1 Bcf of natural gas and 12.6
MMBbls of oil, or an aggregate of approximately 210 Bcfe, 71% of which was
classified as proved developed. Natural gas accounted for 84% of Basin's total
oil and gas production in 1999 and 64% of its proved oil and gas reserves at
year end.

     Basin's Gulf of Mexico properties accounted for 89% of its production in
1999 and 64% of its total proved reserve quantities at the end of the year.
Basin's proved reserves in the Gulf of Mexico at the end of 1999 were
distributed among 25 properties in which Basin owned working interests ranging
from 8% to 100%, averaging 51%. Basin operates 16 of the 25 properties and these
16 properties accounted for approximately two-thirds of Basin's total proved
reserves in the Gulf of Mexico at the end of 1999.

     Most of the proved reserves value attributed to Basin's onshore assets as
of December 31, 1999 was concentrated in six fields in the Powder River and
Green River Basins. This value was broadly distributed among approximately 200
producing wells and a number of undeveloped locations.

     Basin has grown since 1996 primarily through its exploratory drilling
activities. As of December 31, 1999, Basin had assembled undeveloped leasehold
positions totaling 313,061 gross acres, or 193,013 net acres, and had acquired
the rights to Gulf of Mexico 3-D seismic data covering more than 1,100 lease
blocks and 2-D data covering approximately 375,000 miles.

     At September 30, 2000, Basin had 78 employees, including 11 employed in
field operations and 67 employed in its Denver headquarters or Houston division
office. Basin's corporate headquarters is located at 1670 Broadway, Suite 2800,
Denver, Colorado 80202 and its telephone number is (303) 685-8000.

     Additional information concerning Basin and its subsidiaries is included in
the Basin documents filed with the SEC, which are incorporated by reference in
this document. See "Where You Can Find More Information."

BUSINESS OF STONE ENERGY CORPORATION

     Stone is one of the Gulf Coast Basin's leading independent oil and gas
companies. Stone is engaged in the acquisition, exploration, development and
operation of oil and gas properties located onshore and in shallow waters
offshore Louisiana. Stone and its predecessors have been active in the Gulf
Coast Basin since 1973 and have established extensive geophysical, technical and
operational expertise in this area. As of December 31, 1999, Stone had estimated
proved reserves of approximately 251.6 Bcf of natural gas and 22.6 MMBbls of
oil, or an aggregate of approximately 387.4 Bcfe, 80% of which was classified as
proved developed. Stone currently operates all of its 21 properties, which
enables Stone to better control the timing, selection and costs of its drilling
and producing activities.

     Stone's business strategy is to increase production, cash flow and reserves
through the acquisition and development of mature properties located in the Gulf
Coast Basin, either onshore or in shallow waters offshore. Since 1990, Stone has
acquired interests in 21 fields in the Gulf Coast Basin from major and large
independent oil and gas companies, resulting in Stone's majority ownership
interests in 21 properties. Stone believes that there will continue to be
numerous attractive opportunities, in addition to the merger with Basin, to
acquire properties in the Gulf Coast Basin due to the increased focus by major
and large independent companies on projects in deeper waters and in foreign
countries.

                                       69
<PAGE>   78

     As of November 20, 2000, Stone had 139 full time employees. Stone's
corporate headquarters is located at 625 East Kaliste Saloom Road, Lafayette,
Louisiana 70508, and its telephone number is (337) 237-0410. Stone also has
offices in New Orleans, Louisiana and Houston, Texas.

     Additional information concerning Stone and its subsidiaries is included in
the Stone documents filed with the SEC, which are incorporated by reference in
this document. See "Where You Can Find More Information."

PARTNER ACQUISITION CORP.

     Partner Acquisition Corp., a Delaware corporation, is a newly-formed,
wholly-owned subsidiary of Stone Energy Corporation formed for the purpose of
effecting the merger. Partner Acquisition Corp. has no employees.

     Partner Acquisition Corp.'s headquarters are located at 625 East Kaliste
Saloom Road, Lafayette, Louisiana 70508, and its telephone number is (337)
237-0410.

                                       70
<PAGE>   79

                            STONE ENERGY CORPORATION
                         CONDENSED UNAUDITED PRO FORMA
                         COMBINED FINANCIAL STATEMENTS

     On October 28, 2000, Stone and Basin entered into a definitive merger
agreement, under which Basin common stockholders will receive .3974 of a share
of Stone common stock for each share of Basin common stock they own. The
transaction is subject to approval by the stockholders of both companies and to
customary regulatory approval.

     The following condensed unaudited pro forma combined financial statements
are presented to give effect to the merger between Stone and Basin based on the
pooling of interests method of accounting at the exchange ratio of .3974 of a
share of Stone common stock for each share of Basin common stock. The unaudited
pro forma balance sheet data are presented as if the merger was effective on
September 30, 2000. The unaudited pro forma statements of operations data are
presented as if the merger was effective as of the beginning of the earliest
period presented. You should not rely on the pro forma amounts as being
indicative of the financial position or the results of operations of the
combined company that would have actually occurred had the merger been effective
during the periods presented or of the future financial position or future
results of operations of the combined company.

     The unaudited pro forma combined statements of operations exclude
non-recurring charges directly attributable to the merger (estimated at $24
million), substantially all of which will be charged to operations in the
quarter in which the merger is consummated. The unaudited pro forma combined
balance sheet has been adjusted to reflect the assumed after-tax impact of such
non-recurring charges. You should read the condensed unaudited pro forma
combined financial statements in conjunction with the historical consolidated
financial statements and accompanying notes of Stone and Basin incorporated by
reference in this document.

                                       71
<PAGE>   80

                            STONE ENERGY CORPORATION
              CONDENSED UNAUDITED PRO FORMA COMBINED BALANCE SHEET
                               SEPTEMBER 30, 2000
                             (AMOUNTS IN THOUSANDS)

<TABLE>
<CAPTION>
                                              HISTORICAL
                                          -------------------                    PRO FORMA
                                           STONE      BASIN     ADJUSTMENTS    COMBINED STONE
                                          --------   --------   -----------    --------------
<S>                                       <C>        <C>        <C>            <C>
                 ASSETS
----------------------------------------
Current assets:
  Cash and cash equivalents.............  $ 64,379   $  4,519    $                $ 68,898
  Marketable securities, at market......       300         --                          300
  Accounts receivable...................    53,916     25,234                       79,150
  Other current assets..................       130      3,825                        3,955
                                          --------   --------    --------         --------
          Total current assets..........   118,725     33,578                      152,303

Oil and gas properties, net:
  Proved................................   395,508    227,522      18,701(1)       641,731
  Unevaluated...........................    19,617     36,972                       56,589
Building and land, net..................     4,792         --                        4,792
Fixed assets, net.......................     2,952      1,385                        4,337
Other assets, net.......................     3,388        714                        4,102
                                          --------   --------    --------         --------
          Total assets..................  $544,982   $300,171    $ 18,701         $863,854
                                          ========   ========    ========         ========
            LIABILITIES AND
          STOCKHOLDERS' EQUITY
----------------------------------------
Current liabilities:
  Accounts payable to vendors...........  $ 47,391   $ 11,568    $                $ 58,959
  Undistributed oil and gas proceeds....    27,161      8,949                       36,110
  Other accrued liabilities.............     4,141     19,900      24,000(2)        48,041
                                          --------   --------    --------         --------
          Total current liabilities.....    78,693     40,417      24,000          143,110
Long-term debt..........................   100,000     48,000                      148,000
Production payments.....................    12,549         --                       12,549
Deferred tax liability..................    27,679     10,852      (5,180)(2)       39,896
                                                                    6,545(1)
Other long-term liabilities.............     1,196        779                        1,975
                                          --------   --------    --------         --------
          Total liabilities.............   220,117    100,048      25,365          345,530
                                          --------   --------    --------         --------
Common stock............................       185        185        (111)(3)          259
Paid-in capital.........................   257,951    179,903         111(3)       437,965
Retained earnings.......................    66,729     20,035     (18,820)(2)       80,100
                                                                   12,156(1)
                                          --------   --------    --------         --------
          Total stockholders' equity....   324,865    200,123      (6,664)         518,324
                                          --------   --------    --------         --------
          Total liabilities and
            stockholders' equity........  $544,982   $300,171    $ 18,701         $863,854
                                          ========   ========    ========         ========
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       72
<PAGE>   81

                            STONE ENERGY CORPORATION
         CONDENSED UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                      NINE MONTHS ENDED SEPTEMBER 30, 2000
                (AMOUNTS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                               HISTORICAL
                                           ------------------                    PRO FORMA
                                            STONE      BASIN    ADJUSTMENTS    COMBINED STONE
                                           --------   -------   -----------    --------------
<S>                                        <C>        <C>       <C>            <C>
Revenues:
  Oil and gas production.................  $177,839   $84,007     $               $261,846
  Other revenue..........................     2,705       167                        2,872
                                           --------   -------     -------         --------
          Total revenues.................   180,544    84,174                      264,718
                                           --------   -------     -------         --------
Expenses:
  Normal lease operating expenses........    19,563    10,081                       29,644
  Major maintenance expenses.............     5,046        --                        5,046
  Production taxes.......................     4,301     1,367                        5,668
  Depreciation, depletion and
     amortization........................    56,528    31,869      (4,010)(1)       84,387
  Interest...............................     6,263       586                        6,849
  General and administrative expenses....     5,357     4,932                       10,289
                                           --------   -------     -------         --------
          Total expenses.................    97,058    48,835      (4,010)         141,883
                                           --------   -------     -------         --------
Net income before income taxes...........    83,486    35,339       4,010          122,835
                                           --------   -------     -------         --------
Income tax provision:
  Current................................       272        --                          272
  Deferred...............................    28,948    10,852       2,920(4)        42,720
                                           --------   -------     -------         --------
          Total income taxes.............    29,220    10,852       2,920           42,992
                                           --------   -------     -------         --------
Net income...............................  $ 54,266   $24,487     $ 1,090         $ 79,843
                                           ========   =======     =======         ========
Earnings per common share:
  Basic earnings per share...............  $   2.95   $  1.32                     $   3.10
                                           ========   =======     =======         ========
  Diluted earnings per share.............  $   2.89   $  1.30                     $   3.04
                                           ========   =======     =======         ========
  Average shares outstanding.............    18,421    18,497                       25,772
                                           ========   =======     =======         ========
  Diluted shares outstanding.............    18,796    18,826                       26,277
                                           ========   =======     =======         ========
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       73
<PAGE>   82

                            STONE ENERGY CORPORATION
         CONDENSED UNAUDITED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                      NINE MONTHS ENDED SEPTEMBER 30, 1999
                (AMOUNTS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                HISTORICAL
                                            ------------------                   PRO FORMA
                                             STONE      BASIN    ADJUSTMENTS   COMBINED STONE
                                            --------   -------   -----------   --------------
<S>                                         <C>        <C>       <C>           <C>
Revenues:
  Oil and gas production..................  $106,858   $52,750     $              $159,608
  Other revenue...........................     1,361        83                       1,444
                                            --------   -------     -------        --------
          Total revenues..................   108,219    52,833                     161,052
                                            --------   -------     -------        --------
Expenses:
  Normal lease operating expenses.........    16,026     8,352                      24,378
  Major maintenance expenses..............       618        --                         618
  Production taxes........................     2,168       537                       2,705
  Depreciation, depletion and
     amortization.........................    50,708    29,130      (1,473)(1)      78,365
  Interest................................    10,677     2,195                      12,872
  General and administrative expenses.....     4,335     5,153                       9,488
                                            --------   -------     -------        --------
          Total expenses..................    84,532    45,367      (1,473)        128,426
                                            --------   -------     -------        --------
Net income before income taxes............    23,687     7,466       1,473          32,626
                                            --------   -------     -------        --------
Income tax provision:
  Current.................................         5        --                           5
  Deferred................................     8,303        --       3,111(4)       11,414
                                            --------   -------     -------        --------
          Total income taxes..............     8,308        --       3,111          11,419
                                            --------   -------     -------        --------
Net income (loss).........................  $ 15,379   $ 7,466     $(1,638)       $ 21,207
                                            ========   =======     =======        ========
Earnings per common share:
  Basic earnings per share................  $   0.97   $  0.48                    $   0.96
                                            ========   =======     =======        ========
  Diluted earnings per share..............  $   0.95   $  0.47                    $   0.94
                                            ========   =======     =======        ========
  Average shares outstanding..............    15,841    15,600                      22,040
                                            ========   =======     =======        ========
  Diluted shares outstanding..............    16,157    15,943                      22,493
                                            ========   =======     =======        ========
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       74
<PAGE>   83

                            STONE ENERGY CORPORATION
              CONDENSED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          YEAR ENDED DECEMBER 31, 1999
                (AMOUNTS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                HISTORICAL
                                            ------------------                   PRO FORMA
                                             STONE      BASIN    ADJUSTMENTS   COMBINED STONE
                                            --------   -------   -----------   --------------
                                                                         (UNAUDITED)
<S>                                         <C>        <C>       <C>           <C>
Revenues:
  Oil and gas production..................  $146,919   $71,496    $               $218,415
  Other revenue...........................     2,215       134                       2,349
                                            --------   -------    --------        --------
          Total revenues..................   149,134    71,630                     220,764
                                            --------   -------    --------        --------
Expenses:
  Normal lease operating expenses.........    22,625    10,747                      33,372
  Major maintenance expenses..............     1,115        --                       1,115
  Production taxes........................     2,019       914                       2,933
  Depreciation, depletion and
     amortization.........................    65,803    39,494      (2,569)(1)     102,728
  Interest................................    12,840     2,279                      15,119
  General and administrative expenses.....     6,181     6,160                      12,341
                                            --------   -------    --------        --------
          Total expenses..................   110,583    59,594      (2,569)        167,608
                                            --------   -------    --------        --------
Net income before income taxes............    38,551    12,036       2,569          53,156
                                            --------   -------    --------        --------
Income tax provision:
  Current.................................        25        --                          25
  Deferred................................    12,036        --       6,544(4)       18,580
                                            --------   -------    --------        --------
          Total income taxes..............    12,061        --       6,544          18,605
                                            --------   -------    --------        --------
Net income (loss).........................  $ 26,490   $12,036    $ (3,975)       $ 34,551
                                            ========   =======    ========        ========
Earnings per common share:
  Basic earnings per share................  $   1.61   $  0.74                    $   1.51
                                            ========   =======    ========        ========
  Diluted earnings per share..............  $   1.58   $  0.72                    $   1.48
                                            ========   =======    ========        ========
  Average shares outstanding..............    16,469    16,319                      22,954
                                            ========   =======    ========        ========
  Diluted shares outstanding..............    16,789    16,676                      23,416
                                            ========   =======    ========        ========
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       75
<PAGE>   84

                            STONE ENERGY CORPORATION
              CONDENSED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          YEAR ENDED DECEMBER 31, 1998
                (AMOUNTS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                               HISTORICAL
                                           -------------------                   PRO FORMA
                                            STONE      BASIN     ADJUSTMENTS   COMBINED STONE
                                           --------   --------   -----------   --------------
                                                                         (UNAUDITED)
<S>                                        <C>        <C>        <C>           <C>
Revenues:
  Oil and gas production.................  $114,597   $ 48,620    $               $163,217
  Other revenue..........................     2,023         79                       2,102
                                           --------   --------    ---------       --------
          Total revenues.................   116,620     48,699                     165,319
                                           --------   --------    ---------       --------
Expenses:
  Normal lease operating expenses........    18,042      8,276                      26,318
  Major maintenance expenses.............     1,278         --                       1,278
  Production taxes.......................     2,083        770                       2,853
  Depreciation, depletion and
     amortization........................    68,187     29,775        1,090(1)      99,052
  Write-down of oil and gas properties...    89,135     38,500      (13,582)(1)     114,053
  Interest...............................    12,950      2,030                      14,980
  General and administrative expenses....     5,056      4,380                       9,436
                                           --------   --------    ---------       --------
          Total expenses.................   196,731     83,731      (12,492)       267,970
                                           --------   --------    ---------       --------
Net income (loss) before income taxes....   (80,111)   (35,032)      12,492       (102,651)
                                           --------   --------    ---------       --------
Income tax provision (benefit):
  Current................................        --         23                          23
  Deferred...............................   (28,480)    (6,555)        (916)(4)     (35,951)
                                           --------   --------    ---------       --------
          Total income taxes.............   (28,480)    (6,532)        (916)       (35,928)
                                           --------   --------    ---------       --------
Net income (loss)........................  $(51,631)  $(28,500)   $  13,408       $(66,723)
                                           ========   ========    =========       ========
Loss per common share:
  Basic loss per share...................  $  (3.43)  $  (2.06)                   $  (3.24)
                                           ========   ========    =========       ========
  Diluted loss per share.................  $  (3.43)  $  (2.06)                   $  (3.24)
                                           ========   ========    =========       ========
  Average shares outstanding.............    15,066     13,859                      20,574
                                           ========   ========    =========       ========
  Diluted shares outstanding.............    15,066     13,859                      20,574
                                           ========   ========    =========       ========
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       76
<PAGE>   85

                            STONE ENERGY CORPORATION
              CONDENSED PRO FORMA COMBINED STATEMENT OF OPERATIONS
                          YEAR ENDED DECEMBER 31, 1997
                (AMOUNTS IN THOUSANDS, EXCEPT PER SHARE AMOUNTS)

<TABLE>
<CAPTION>
                                                HISTORICAL
                                             -----------------                   PRO FORMA
                                              STONE     BASIN    ADJUSTMENTS   COMBINED STONE
                                             -------   -------   -----------   --------------
                                                                         (UNAUDITED)
<S>                                          <C>       <C>       <C>           <C>
Revenues:
  Oil and gas production...................  $69,079   $24,401    $               $93,480
  Other revenue............................    1,908       319                      2,227
                                             -------   -------    --------        -------
          Total revenues...................   70,987    24,720                     95,707
                                             -------   -------    --------        -------
Expenses:
  Normal lease operating expenses..........   10,123     4,600                     14,723
  Major maintenance expenses...............    1,844        --                      1,844
  Production taxes.........................    2,215     1,260                      3,475
  Depreciation, depletion and
     amortization..........................   28,739    10,622       1,022(1)      40,383
  Interest.................................    4,916       764                      5,680
  General and administrative expenses......    4,736     3,694                      8,430
                                             -------   -------    --------        -------
          Total expenses...................   52,573    20,940       1,022         74,535
                                             -------   -------    --------        -------
Net income (loss) before income taxes......   18,414     3,780      (1,022)        21,172
                                             -------   -------    --------        -------
Income tax provision (benefit):
  Current..................................       --      (471)                      (471)
  Deferred.................................    6,495     1,795        (409)(4)      7,881
                                             -------   -------    --------        -------
          Total income taxes...............    6,495     1,324        (409)         7,410
                                             -------   -------    --------        -------
Net income (loss)..........................  $11,919   $ 2,456    $   (613)       $13,762
                                             =======   =======    ========        =======
Earnings per common share:
  Basic earnings per share.................  $  0.79   $  0.22                    $  0.71
                                             =======   =======    ========        =======
  Diluted earnings per share...............  $  0.78   $  0.22                    $  0.70
                                             =======   =======    ========        =======
  Average shares outstanding...............   15,024    11,228                     19,486
                                             =======   =======    ========        =======
  Diluted shares outstanding...............   15,230    11,345                     19,739
                                             =======   =======    ========        =======
</TABLE>

   See accompanying notes to condensed unaudited pro forma combined financial
                                  statements.

                                       77
<PAGE>   86

                            STONE ENERGY CORPORATION
                     NOTES TO CONDENSED UNAUDITED PRO FORMA
                         COMBINED FINANCIAL STATEMENTS

A. BASIS OF PRESENTATION

     Stone expects to account for the merger using the pooling of interests
method of accounting. Accordingly, Stone's and Basin's historical balance sheets
and statements of operations will be consolidated as if the two companies had
always been combined. The accompanying condensed unaudited pro forma combined
balance sheet is presented as if the merger of Stone and Basin was effective as
of September 30, 2000. The condensed unaudited pro forma combined statements of
operations are presented as if the merger of Stone and Basin was effective as of
the beginning of the earliest period presented. Under the terms of the merger
agreement, Stone stockholders will retain their shares and each share of Basin
common stock will be exchanged for .3974 of a share of Stone common stock.

     In the opinion of management, these pro forma combined financial statements
include all adjustments necessary for a fair presentation of the condensed
unaudited pro forma combined financial statements. Accounting policies used in
the preparation of the pro forma statements are those disclosed in Stone's and
Basin's historical consolidated financial statements, which are incorporated by
reference herein. Except for the difference between Stone's historical future
gross revenue method and Basin's historical units of production method for
calculating depreciation, depletion and amortization of oil and gas properties,
the adjustments needed to conform the accounting policies of Stone and Basin are
insignificant.

     The condensed unaudited pro forma combined financial statements are not
necessarily indicative either of the results that actually would have been
achieved if the transactions reflected therein had been effective during the
periods presented or of the results that may be obtained in the future. In
preparing these pro forma statements, no adjustments have been made to reflect
transactions that have occurred since the dates of the pro forma financial
statements.

     The condensed unaudited pro forma combined financial statements should be
read in conjunction with the description of the merger of Stone and Basin
elsewhere in this document, the historical financial statements and related
notes of Stone, incorporated by reference in this document, and the historical
financial statements and related notes of Basin, incorporated by reference in
this document.

B. PRO FORMA ADJUSTMENTS

     The condensed unaudited pro forma combined financial statements give effect
to the following assumptions and adjustments:

        1. Adjustments to reflect property impairment and depreciation,
           depletion and amortization of oil and gas properties as if both
           companies had been combined as of January 1, 1997.

        2. Merger costs, including severance and related costs, fees for
           advisors, attorneys and other consultants and incremental direct
           costs of completing the merger, are estimated to be approximately $24
           million (approximately $19 million after tax) substantially all of
           which will be charged to expense upon consummation of the merger. For
           the purposes of the condensed pro forma balance sheet, these
           transaction costs, net of the related income tax effect, have been
           recorded as a reduction in retained earnings. These one-time merger
           costs are not reflected in the condensed pro forma statements of
           operations since they are non-recurring in nature.

        3. The issuance by Stone of .3974 of a Stone common share for each share
           of Basin common stock.

        4. Adjustments to reflect the income tax provision for the pro forma
           combined statements of operations at an effective tax rate of 35%.

                                       78
<PAGE>   87
                     NOTES TO CONDENSED UNAUDITED PRO FORMA
                         COMBINED FINANCIAL STATEMENTS
                                  (CONTINUED)

     Net income (loss) per average common share outstanding has been calculated
based upon the pro forma weighted average number of shares outstanding for each
period presented. To compute the combined company pro forma basic and diluted
net income (loss) per share, Stone's historical weighted average number of basic
and diluted shares outstanding were increased in each period by the historical
weighted average number of Basin basic and diluted shares outstanding,
multiplied by the exchange ratio of .3974.

                                       79
<PAGE>   88

                       COMPARISON OF STOCKHOLDERS' RIGHTS

     As a result of the merger, the holders of Basin common stock will become
holders of Stone common stock. The rights of the stockholders of Stone will be
governed by applicable Delaware law, including the Delaware General Corporation
Law, or DGCL, and by Stone's certificate of incorporation and by-laws.

     The following is a summary of the material differences between the rights
of Stone stockholders and Basin stockholders. Because both Stone and Basin are
organized under the laws of the State of Delaware, these differences arise
principally from differences between the Stone certificate of incorporation and
the Basin certificate of incorporation, and differences between Stone's by-laws
and Basin's by-laws.

     The following summaries do not purport to provide a complete description of
the specific rights of Stone stockholders under Stone's certificate of
incorporation and by-laws as compared with the rights of Basin stockholders
under Basin's certificate of incorporation and by-laws. The identification of
specific differences in the rights of these holders as material is not intended
to indicate that other equally important or more significant differences do not
exist. These summaries are qualified in their entirety by reference to the
governing corporate instruments of Stone and Basin to which stockholders are
referred.

AUTHORIZED CAPITAL STOCK

     The total number of authorized shares of capital stock of Stone is
30,000,000, consisting of 25,000,000 shares of common stock, par value $0.01 per
share, and 5,000,000 shares of preferred stock, par value $0.01 per share. In
connection with the merger, holders of Stone common stock will vote on a
proposal to amend Stone's certificate of incorporation to increase the number of
authorized shares of common stock to             shares.

     The total number of authorized shares of capital stock of Basin is
60,000,000, consisting of 50,000,000 shares of common stock, par value $0.01 per
share, and 10,000,000 shares of preferred stock, par value $0.01 per share.

DIRECTORS

     The board of directors of Stone has 10 members and will be increased to 11
members at the effective time of the merger to add Michael S. Smith, Chairman of
the Board, President and Chief Executive Officer of Basin, to Stone's board. The
Stone by-laws provide that the Stone board of directors will consist of a number
of directors to be fixed from time to time by resolution of the board of
directors, but in no event shall there be more than 12 directors in the
aggregate. The Basin board of directors has eight members. The Basin by-laws
provide that the Basin board of directors will consist of a number of directors,
not less than three nor greater than 12, to be fixed from time to time
exclusively by resolutions of the Basin board of directors.

     Delaware law permits, but does not require, a classified board of directors
with staggered terms under which one-half to one-third of the directors are
elected for terms of two or three years, respectively. Both the Basin board and
the Stone board are divided into three separate classes, consisting, as nearly
as possible, of equal numbers of directors, with one class being elected
annually. Members of both boards of directors are elected to serve a terms of
three years and until their successors are elected and qualified.

AMENDMENT OF BY-LAWS

     Under Delaware law, an amendment to a corporation's by-laws requires the
approval of the stockholders, unless the certificate of incorporation confers
the power to amend the by-laws upon the board of directors. Delaware law
requires that stockholders always have the power to make, alter or repeal by-
laws, even when the directors are also delegated such power.

     The Stone certificate of incorporation expressly authorizes the Stone board
of directors to adopt, amend or repeal the by-laws of the corporation or adopt
new by-laws, without any action on the part of the stockholders. However, no
such adoption, amendment or repeal is valid with respect to by-law provisions
that have been

                                       80
<PAGE>   89

adopted, amended, or repealed by the stockholders. Further, by-laws adopted or
amended by the board and any powers thereby conferred may be amended, altered,
or repealed by the stockholders.

     The Basin certificate of incorporation provides that the Basin board of
directors has the power to make, alter, amend and repeal the by-laws (except to
the extent that the by-laws adopted by the stockholders shall otherwise
provide). Any by-laws adopted by the Basin board may be altered, amended or
repealed by the directors or the stockholders. Notwithstanding the foregoing and
anything in the certificate of incorporation to the contrary, the Basin
certificate provides that Articles II and III of the by-laws (concerning the
registered address of the corporation, the registered agent, and the nature of
the business) shall not be altered, amended or repealed without the affirmative
vote of the holders of at least 80% of the voting power of all of the shares of
the corporation entitled to vote generally in the election of directors, voting
together as a single class.

AMENDMENT OF CERTIFICATE

     Under Delaware law, an amendment to the certificate of incorporation
requires the approval of the corporation's board of directors and the
affirmative vote of a majority of the outstanding shares entitled to vote. In
addition, amendments that make changes relating to the capital stock by
increasing or decreasing the par value or the aggregate number of authorized
shares of a class, or otherwise adversely affecting the rights of such class,
must be approved by the majority vote of each class or series of stock affected,
even if such stock would not otherwise have such voting rights.

     The Basin certificate of incorporation further requires the affirmative
vote of the holders of at least 80% of the voting power of all of the then
outstanding shares of the corporation entitled to vote generally in the election
of directors, voting together as a single class, to alter, amend, or adopt any
provision inconsistent with, or repeal, both Article V of the corporation's
certificate of incorporation, which deals generally with election and removal of
directors, stockholder action, and by-law amendments, and Article VI, which
details the higher voting requirements for certain business combinations.

REMOVAL OF DIRECTORS

     Under the Stone by-laws, any one or more directors or the entire board of
directors may be removed for cause by the holders of a majority of the shares
then entitled to vote at an election of directors.

     Under the Basin certificate of incorporation, any director, or the entire
board of directors, may be removed from office at any time (i) with cause by the
affirmative vote of the holders of at least a majority of the voting power or
all of the then outstanding shares of the corporation entitled to vote generally
in the election of directors, voting together as a single class, or (ii) without
cause by the affirmative vote of the holders of at least 80% of the voting power
of all of the then outstanding shares of the corporation entitled to vote
generally in the election of directors, voting together as a single class.

FILLING VACANCIES ON THE BOARD OF DIRECTORS

     The Stone by-laws provide that vacancies on the Stone board of directors
and newly created directorships resulting from any increase in the authorized
number of directors elected by all of the stockholders having the right to vote
as a single class may be filled only by the affirmative vote of a majority of
the directors then in office, although less than a quorum, or by a sole
remaining director. The by-laws further provide that if the Stone certificate of
incorporation entitles the holders of any class or classes of stock or series
thereof to elect one or more directors, vacancies and newly created
directorships of such class or classes or series may be filled only by a
majority of the directors elected by such class or classes or series thereof
then in office, or by a sole remaining director so elected.

     Under the Basin certificate of incorporation, any vacancy in the board of
directors, whether by an increase in the number of directors or vacancies on the
board resulting from death, resignation, disqualification, removal or other
cause, may be filled solely by a majority of the remaining directors then in
office, even if less than a quorum of the board of directors.

                                       81
<PAGE>   90

     Both the Stone by-laws and the Basin certificate of incorporation provide
that any director elected to fill vacancies or newly created directorships shall
hold office for the remainder of the full term of the class of directors in
which the new directorship was created or the vacancy occurred and until such
director's successor has been elected and qualified.

STOCKHOLDER MEETINGS

     The Stone by-laws provide that a special meeting of stockholders for any
proper purpose or purposes may be called at any time by the chairman of the
board, the president, a majority of the board of directors, or a majority of the
executive committee. Special meetings of the stockholders may not be called by
any other person or persons. Only business within the proper purpose or purposes
described in the notice required by Stone's by-laws may be conducted at a
special meeting of the stockholders.

     The Basin by-laws provide that special meetings of stockholders may be
called only by the chairman of the board, the president and chief executive
officer, or the board of directors pursuant to a resolution approved by a
majority of the entire board of directors.

QUORUM

     Pursuant to both the Stone by-laws and the Basin by-laws, a quorum for the
transaction of business at any meeting of the board of directors consists of a
majority of the entire board of directors.

     Under the Stone by-laws, a quorum for the transaction of business at any
stockholder meeting consists of the holders of a majority of the shares of
voting stock issued and outstanding and entitled to vote, present in person or
represented by proxy. Pursuant to the Basin by-laws, a quorum for the
transaction of business at any stockholder meeting consists of not less than
one-third of the shares entitled to vote at any meeting of the stockholders,
present in person or by proxy.

PREEMPTIVE RIGHTS

     Under Delaware law, stockholders have no preemptive rights unless such
rights are provided for in the certificate of incorporation. Neither the Stone
certificate nor the Basin certificate grants any preemptive rights to
stockholders.

VOTING BY STOCKHOLDERS

     Under the Stone by-laws, unless otherwise required by law, the Stone
certificate of incorporation or the Stone by-laws, action by Stone stockholders
is taken by the vote of the holders of a majority of the votes cast, except for
elections, which are determined by a plurality of the votes cast, at a meeting
of stockholders at which a quorum is present.

     Pursuant to the Basin by-laws, action by Basin stockholders is taken by the
vote of the holders of a majority of the stock represented and entitled to vote
at a stockholders meeting at which a quorum is present, subject to applicable
law, the Basin certificate of incorporation or the Basin by-laws.

STOCKHOLDER ACTION WITHOUT A MEETING

     Under Delaware law, unless otherwise provided in the certificate of
incorporation, stockholders may take any action on which they are required or
permitted to vote without a meeting if a written consent is signed by the
holders of outstanding stock having not less than the minimum number of votes
that would be required to authorize or take such action at a meeting at which
all shares entitled to vote thereon were present and voted.

     The Stone by-laws provide that the written consent of all of the holders of
the outstanding stock entitled to vote thereon is necessary for stockholder
action without a meeting. The Basin certificate of incorporation prohibits
stockholder action by written consent, unless there are three or less
stockholders and a written consent is signed by the holders of outstanding stock
having not less than 80% of the votes that would be necessary to authorize or
take such action at a meeting at which all shares entitled to vote were present
and voted.

                                       82
<PAGE>   91

RIGHTS PLAN

     In October 1998, Stone adopted a stockholder rights plan and entered into a
rights agreement with ChaseMellon Shareholder Services, L.L.C. as rights agent.
Under the Stone rights agreement, one right attaches to each outstanding Stone
common share. Each right, when exercisable, entitles its registered holder to
purchase from Stone one one-thousandth of a share of junior participating
preferred stock at an exercise price of $125.00, subject to adjustment. The
rights become exercisable only if a person or entity, or the affiliates,
associates, or successors thereof, acquires 15% or more of shares of Stone
common stock or announces a tender offer for 15% or more of shares of Stone
common stock, subject to certain exceptions specified in the Stone rights
agreement. The rights agreement has been amended to exclude the acquisition of
shares of Stone common stock by Basin, or any of its associates or affiliates,
as triggering events under the plan. Neither the execution of the merger
agreement nor the consummation of the transactions contemplated thereby will
result in these rights being exercised, distributed or triggered.

     In February 1996, Basin adopted a stockholders rights plan and entered into
a rights agreement with Corporate Stock Transfer, Inc. as rights agent. Under
the Basin rights agreement, one preferred stock purchase right attaches to each
share of Basin common stock. Each right, when exercisable, entitles its
registered holder to purchase from Basin one one-hundredth of a share of junior
participating preferred stock at an exercise price of $18.75, subject to
adjustment. The rights become exercisable only if any person or entity, or the
successor thereof, acquires, without the prior approval of Basin, 15% or more of
shares of the Basin common stock then outstanding or announces a tender offer
for 15% or more of shares of Basin common stock, subject to certain exceptions
specified in the Basin rights agreement. The rights agreement has been amended
to exclude the acquisition of shares of Basin common stock by Stone or Partner
Acquisition Corp., or any of their associates or affiliates, as triggering
events under the plan. Neither the execution of the merger agreement nor the
consummation of the transactions contemplated thereby will result in these
rights being exercised, distributed or triggered.

     The rights granted under the Stone and Basin rights agreements have similar
anti-takeover effects, each causing substantial dilution to a person or group
that attempts to acquire, or merge with, either company without conditioning the
offer on the rights being rendered inapplicable.

BUSINESS COMBINATIONS

     Under the Delaware business combination statute, a corporation is
prohibited from engaging in any business combination with an interested
stockholder who, together with its affiliates or associates, owns, or who is an
affiliate or associate of the corporation and within a three-year period did
own, 15% or more of the corporation's voting stock for a three-year period
following the time the stockholder became an interested stockholder, unless:

     - prior to the time the stockholder became an interested stockholder, the
       board of directors of the corporation approved either the business
       combination or the transaction that resulted in the stockholder becoming
       an interested stockholder;

     - the interested stockholder owned at least 85% of the voting stock of the
       corporation, excluding specified shares, upon consummation of the
       transaction that resulted in the stockholder becoming an interested
       stockholder; or

     - at or subsequent to the time the stockholder became an interested
       stockholder, the business combination is approved by the board of
       directors of the corporation and authorized by the affirmative vote, at
       an annual or special meeting and not by written consent, of at least
       two-thirds of the outstanding voting shares of the corporation, excluding
       shares held by that interested stockholder.

     A business combination generally includes:

     - mergers, consolidations and sales or other dispositions of 10% or more of
       the assets of a corporation to or with an interested stockholder;

                                       83
<PAGE>   92

     - specified transactions resulting in the issuance or transfer to an
       interested stockholder of any capital stock of the corporation or its
       subsidiaries; and

     - other transactions resulting in a disproportionate financial benefit to
       an interested stockholder.

     The Delaware business combination statute does not apply to a corporation
if the certificate of incorporation or by-laws of the corporation contain a
provision expressly electing not to be governed by the provisions of the
statute.

     Stone has not adopted any provision in its certificate of incorporation or
its by-laws opting out of the Delaware business combination statute or otherwise
discussing business combinations with interested stockholders.

     The Basin certificate of incorporation requires the affirmative vote of the
holders of at least two-thirds of the outstanding shares of Basin entitled to
vote, not beneficially owned by any interested stockholder and voting together
as a single class, for certain business combinations with interested
stockholders:

     - any merger or consolidation of Basin or any subsidiary with (i) any
       interested stockholder or (ii) any other corporation which is, or after
       the merger or consolidation would be, an affiliate; and

     - any sale, lease, exchange, mortgage, pledge, transfer or other
       disposition to or with any interested stockholder or any affiliate
       thereof of any assets of Basin or any Basin subsidiary having an
       aggregate fair market value equal to or greater than 15% of Basin's
       assets; or

     - the issuance or transfer by Basin or any Basin subsidiary of any
       securities of Basin or any subsidiary to any interested stockholder or
       any affiliate thereof in exchange for cash, securities or other property,
       which cash, securities or other property has an aggregate fair market
       value equal to or greater than 15% of Basin's assets; or

     - the adoption of any plan or proposal for the liquidation or dissolution
       of Basin, proposed by or on behalf of any interested stockholder or any
       affiliate thereof; or

     - any reclassification of securities, recapitalization, reorganization,
       merger or consolidation of Basin or any other transaction (whether or not
       involving an interested stockholder) which has the effect, directly or
       indirectly, of increasing the proportionate share of the outstanding
       shares of any class of equity security of Basin or any subsidiary which
       is beneficially owned by an interested stockholder or any affiliate
       thereof.

This two-thirds vote is not required, however, if: (1) the business combination
has been approved by a majority of disinterested directors, or (2) certain price
and procedure requirements, enumerated in the Basin certificate of
incorporation, have been met.

     The Delaware business combination statute is not applicable to the business
combination of Basin and Stone because the Basin board of directors has approved
this transaction.

INDEMNIFICATION AND LIMITATION OF LIABILITY

     Delaware law permits corporations to adopt a provision in their certificate
of incorporation eliminating the liability of a director to the corporation or
its stockholders for monetary damages for breach of the director's fiduciary
duty of care. A Delaware corporation may indemnify any person who is a party in
any civil, criminal, administrative or investigative, pending or completed
action, suit or proceeding (other than an action by or in the right of the
corporation) by reason of the fact that he or she is or was a director, officer,
employee or agent of the corporation, or is or was serving at the request of the
corporation as such for another entity, against judgments, fines, amounts paid
in settlement and expenses (including attorneys' fees), actually and reasonably
incurred by such person in connection with any threatened, pending or completed
action, suit or proceeding.

     With respect to actions by or in the right of the corporation, Delaware law
authorizes indemnification of such person against expenses (including attorneys'
fees) actually and reasonably incurred by him or her

                                       84
<PAGE>   93

in connection with the defense or settlement of such action or suit. A person
must have acted in good faith and in a manner he or she reasonably believed to
be in the best interests of the corporation, and, with respect to any criminal
action or proceeding, had no reasonable cause to believe his or her conduct was
unlawful with respect to those actions taken by or in the right of the
corporation. Court approval is required as a prerequisite to indemnification of
expenses for any claim as to which a person has been adjudged liable to the
corporation.

     Delaware law requires indemnification against expenses actually and
reasonably incurred by any director, officer, employee or agent in connection
with a proceeding against such person for actions in such capacity to the extent
that the person has been successful on the merits or otherwise. Advancement of
expenses prior to a determination on the merits is permitted, but not required.
Any director or officer must undertake to repay such expenses if it is
ultimately determined that he or she is not entitled to indemnification. The
disinterested members of the board of directors (or independent legal counsel or
the stockholders) must determine, in each instance where indemnification is not
required by Delaware law, that such director, officer, employee or agent is
entitled to indemnification. Delaware law provides that the indemnification
provided by statute is not exclusive.

     The Stone certificate of incorporation provides that the directors of Stone
are not personally liable to Stone or its stockholders for damages for breach of
duty as a director, except for such liability as is expressly not subject to
limitation under the DGCL. The Stone by-laws provide that Stone shall, to the
fullest extent permitted by law, indemnify any person, or such person's heirs,
executor, or administrator, who is or was or has agreed to become a director or
officer, or is or was serving or has agreed to serve at the request of Stone as
a director, officer, partner, venturer, proprietor, trustee, employee, agent, or
similar functionary of another foreign or domestic corporation, partnership,
joint venture, sole proprietorship, trust, employee benefit plan or other
enterprise, whether the basis of such proceeding is alleged action in an
official capacity as officer or director or in any other capacity while serving
or having agreed to serve as an officer or director. Indemnification is possible
when such person is made or threatened to be made a party to any threatened,
pending or completed action or proceeding, whether civil, criminal,
administrative, arbitrative, or investigative (other than an action by or in the
right of the corporation), by reason of the fact that such person is or was a
director or elected officer of Stone or is serving or served such other
organization in any capacity, against all reasonable expense, liability and loss
(including without limitation, attorneys' fees, judgments, fines, excise or
similar taxes, punitive damages or penalties and amounts paid or to be paid in
settlement) actually incurred by such person in connection with such proceeding,
provided that such proceeding (or part thereof) was authorized by the board of
directors. The Stone by-laws expressly acknowledge that such indemnification
could involve indemnification for negligence or under theories of strict
liability. Stone may, by action of its board of directors, indemnify employees
and agents of the corporation with the same scope and effect as the
indemnification of directors and officers.

     The Basin certificate of incorporation provides that Basin shall indemnify,
to the full extent permitted by Delaware law, any person against all liability
and expense incurred because such person was a director or officer of Basin, or
while serving as a director or officer of Basin, he or she is or was serving at
the request of Basin as a director, officer, partner or trustee of, or in any
similar managerial or fiduciary position of, or as an employee or agent of
another corporation, partnership, joint venture, association or other
enterprise, or by reason of any action alleged to have been taken or omitted in
such capacity. No director will be personally liable for monetary damages for
breach of fiduciary duties, except for liability for (a) any breach of the
director's duty of loyalty to Basin or its stockholders; (b) acts or omissions
not in good faith or involving intentional misconduct or knowing violations of
law; (c) the payment of unlawful dividends or unlawful stock repurchases or
redemptions; or (d) transactions from which the director derived an improper
personal benefit. These provisions do not preclude Basin from indemnifying other
persons from similar or other expenses and liabilities as the board of directors
or the stockholders may determine in a specific instance or by resolution of
general application. The Basin by-laws provide that any indemnification and
advancement of expenses will continue as to a person who is no longer a director
or officer and will inure to the heirs, executors, and administrators of such
person.

                                       85
<PAGE>   94

                             PROPOSED AMENDMENT TO
                      STONE'S CERTIFICATE OF INCORPORATION

     Stone's board of directors has approved a proposal authorizing an amendment
to Stone's certificate of incorporation to increase the authorized shares of
Stone's common stock. The certificate of amendment to effect this increase is in
the form attached to this joint proxy statement/prospectus as Annex D. Approval
of this proposed amendment requires the affirmative vote of the holders of a
majority of all outstanding shares of Stone's common stock. Approval of the
proposal to amend Stone's certificate of incorporation is a prerequisite to
approval of the proposal for the share issuance.

     Stone is currently authorized to issue up to 30,000,000 shares of capital
stock, of which 5,000,000 are shares of preferred stock, $0.01 par value per
share, and 25,000,000 are shares of common stock, $0.01 par value per share. The
proposed amendment would increase the authorized shares of Stone's capital stock
to             , which would consist of 5,000,000 shares of preferred stock,
$0.01 par value per share, and             shares of common stock, $0.01 par
value per share.

     The adoption of the amendment to Stone's certificate of incorporation is a
prerequisite to the issuance of shares of Stone common stock in connection with
the merger and is intended to facilitate the issuance of shares of Stone common
stock in the future upon the exercise of options or for other purposes
determined by Stone's board of directors to be in the best interests of Stone
and its stockholders.

     The principal effect of the issuance of shares of Stone common stock in
connection with the merger and any additional issuances of shares of Stone
common stock in the future is to dilute the relative ownership interests of
Stone stockholders. In the merger, Basin stockholders will become Stone
stockholders and will own approximately 29% of the shares of Stone common stock
that are outstanding after the merger. Current Stone stockholders will own the
remaining approximately 71%. After giving effect to the amendment proposal, and
taking into account such shares of Stone common stock to be issued in connection
with the merger, approximately       shares of Stone common stock will be
available for future issuance by the board of directors without further action
by the stockholders.

     Assuming the certificate amendment is approved and implemented, the
certificate of amendment amending Stone's certificate of incorporation will be
filed with the Secretary of State of Delaware as promptly as practicable
thereafter. The amendment would become effective as of the close of business on
the date of such filing.

                             LEGAL AND TAX MATTERS

     The validity of the shares of Stone common stock to be issued in the merger
will be passed upon for Stone by Vinson & Elkins L.L.P., counsel to Stone.
Vinson & Elkins L.L.P. will also render an opinion that the merger will qualify
as a "reorganization" within the meaning of Section 368(a) of the Internal
Revenue Code.

     Brobeck, Phleger & Harrison LLP, counsel to Basin, will render an opinion
that the merger will qualify as a "reorganization" within the meaning of Section
368(a) of the Internal Revenue Code.

                                    EXPERTS

     The financial statements of Stone as of December 31, 1999 and 1998, and for
each of the years in the three-year period ended December 31, 1999, incorporated
by reference herein, have been audited by Arthur Andersen LLP, independent
public accountants, as indicated in their report with respect thereto, and are
incorporated by reference herein in reliance upon the authority of said firm as
experts in accounting and auditing in giving said reports.

     With respect to the unaudited interim financial information for the
quarters ended September 30, 2000 and 1999, June 30, 2000 and 1999 and March 31,
2000 and 1999, Arthur Andersen LLP has applied limited procedures in accordance
with professional standards for a review of that information. However,

                                       86
<PAGE>   95

their separate reports thereon state that they did not audit and they do not
express an opinion on that interim financial information. Accordingly, the
degree of reliance on their reports on that information should be restricted in
light of the limited nature of the review procedures applied. In addition, the
accountants are not subject to the liability provisions of Section 11 of the
Securities Act of 1933 for their report on the unaudited interim financial
information because that report is not a "report" or a "part" of the
registration statement prepared or certified by the accountants within the
meaning of Sections 7 and 11 of the Securities Act.

     The consolidated financial statements of Basin incorporated by reference in
this joint proxy statement/ prospectus, to the extent and for the periods
indicated in their report, have been audited by Arthur Andersen LLP, independent
public accountants, and are incorporated by reference herein in reliance upon
the authority of said firm as experts in accounting and auditing in giving said
reports.

                         INDEPENDENT PUBLIC ACCOUNTANTS

     Representatives of Arthur Andersen LLP, current independent certified
accountants of Stone and Basin, expect to be present at the Stone and Basin
special meetings and will be available to respond to appropriate questions from
Stone and Basin stockholders, respectively, in attendance. Although these
representatives have stated that they do not intend to make any statements at
the Stone or Basin special meetings, they will have the opportunity to do so.

                                 OTHER MATTERS

     Pursuant to the Stone by-laws, the business that may be conducted at the
Stone special meeting is confined to the purposes described in the notice of
special meeting of stockholders that accompanies this document.

     Pursuant to Basin's by-laws, the business that may be conducted at the
Basin special meeting is confined to the purposes described in the notice of
special meeting of stockholders that accompanies this document.

                             STOCKHOLDER PROPOSALS

     Any Stone stockholder who intends to present a proposal at Stone's 2001
annual meeting of stockholders for inclusion in the proxy statement and form of
proxy relating to that meeting is advised that the proposal must be received by
the Secretary of Stone at its principal executive offices not later than
            , 2000. Stone will not be required to include in its proxy statement
a form of proxy or stockholder proposal that is received after that date or that
otherwise fails to meet the requirements for stockholder proposals established
by regulations of the SEC.

     If the merger is consummated as currently contemplated, there will be no
2001 annual meeting of Basin stockholders. However, if it is not consummated as
intended, any Basin stockholder who intends to present a proposal at Basin's
2001 annual meeting of stockholders for inclusion in the proxy statement and
form of proxy relating to that meeting is advised that the proposal must be
received by the Secretary of Basin at its principal executive offices not later
than           , 2000. Stockholders can present other proposals from the floor
of the annual meeting only if, in general, the corporate secretary receives
proper notice and certain information not less than 60 days nor more than 90
days prior to the meeting. Any stockholder who wishes to introduce a proposal
should consult Basin's certificate of incorporation and by-laws and the
applicable proxy rules of the SEC. Basin will not be required to include in its
proxy statement a form of proxy or stockholder proposal that is received after
that date or that otherwise fails to meet the requirements for stockholder
proposals established by regulations of the SEC.

                                       87
<PAGE>   96

                      WHERE YOU CAN FIND MORE INFORMATION

     Stone has filed with the SEC a registration statement on Form S-4 under the
Securities Act that registers the issuance of the shares of Stone common stock
in the merger to Basin stockholders. The registration statement, including the
attached exhibits and schedules, contains additional relevant information about
Stone and Basin. The rules and regulations of the SEC allow us to omit certain
information included in the registration statement from this document. You can
inspect and copy the registration statement at the addresses below or you can
review it on the SEC's website as set forth below.

     In addition, Stone and Basin file reports, proxy statements and other
information with the SEC under the Securities Exchange Act of 1934, as amended.
Please call the SEC at 1-800-SEC-0330 for further information on the public
reference rooms. You may read and copy this information at the following
locations of the SEC:

<TABLE>
<S>                          <C>                           <C>
Public Reference Room        New York Regional Office      Chicago Regional Office
450 Fifth Street, N.W. Room  7 World Trade Center Suite    Citicorp Center
1024                         1300                          500 West Madison Street
Washington, D.C. 20549       New York, New York 10048      Suite 1400
                                                           Chicago, Illinois
                                                           60661-2511
</TABLE>

     You may also obtain copies of this information by mail from the Public
Reference Section of the SEC, 450 Fifth Street, N.W., Room 1024, Washington,
D.C. 20549, at prescribed rates. The SEC also maintains an Internet website that
contains reports, proxy statements and other information about issuers, like
Stone and Basin, who file electronically with the SEC. The address of that
website is http://www.sec.gov. You can also inspect reports, proxy statements
and other information about Stone at the offices of the NYSE, 20 Broad Street,
New York, New York 10005 and about Basin at the offices of the National
Association of Securities Dealers, 1735 K Street, Washington, D.C. 20006.

     The SEC allows Stone and Basin to incorporate by reference information into
this document. This means that the companies can disclose important information
to you by referring you to another document filed separately with the SEC and
not included in, or delivered with, this document. The information incorporated
by reference is considered to be a part of this document, except for any
information that is superseded by information that is included directly in this
document.

     This document incorporates by reference the documents listed below that
Stone and Basin have previously filed with the SEC. They contain important
information about our companies and their financial condition. Some of these
filings have been amended by later filings, which are also listed.

<TABLE>
<CAPTION>
STONE COMMISSION FILINGS
(FILE NO. 001-12074)                                        DESCRIPTION OR PERIOD
------------------------                                    ---------------------
<S>                                             <C>
Quarterly Report on Form 10-Q................   Quarter Ended September 30, 2000
Quarterly Report on Form 10-Q................   Quarter Ended June 30, 2000
Quarterly Report on Form 10-Q................   Quarter Ended March 31, 2000
Proxy Statement on Schedule 14A..............   For Stone's 2000 annual meeting of
                                                stockholders   held on May 18, 2000
Annual Report on Form 10-K...................   Year Ended December 31, 1999
Current Report on Form 8-K...................   Press release, dated October 30, 2000,
                                                announcing merger agreement between Stone and
                                                Basin
</TABLE>

                                       88
<PAGE>   97

<TABLE>
<CAPTION>
BASIN COMMISSION FILINGS
(FILE NO. 000-20125)                                        DESCRIPTION OR PERIOD
------------------------                                    ---------------------
<S>                                             <C>
Quarterly Report on Form 10-Q................   Quarter Ended September 30, 2000
Quarterly Report on Form 10-Q................   Quarter Ended June 30, 2000
Quarterly Report on Form 10-Q................   Quarter Ended March 31, 2000
Proxy Statement on Schedule 14A..............   For Basin's 2000 annual meeting of
                                                stockholders   held on May 11, 2000
Annual Report on Form 10-K...................   Year Ended December 31, 1999
Current Report on Form 8-K...................   Report of merger agreement dated as of
                                                October 28, 2000 among Stone, Basin and
                                                Partner Acquisition Corp.
</TABLE>

     Stone and Basin incorporate by reference additional documents that either
company may file with the SEC pursuant to Section 13(a), 13(c), 14 or 15(d) of
the Exchange Act between the date of this document and the dates of the Stone
special meeting and the Basin special meeting. These documents include periodic
reports, such as annual reports on Form 10-K, quarterly reports on Form 10-Q and
current reports on Form 8-K, as well as proxy statements.

     You can obtain any of the documents incorporated by reference in this
document through Stone or Basin, as the case may be, or from the SEC through the
SEC's website at the address described above. Documents incorporated by
reference are available from the companies without charge, excluding any
exhibits to those documents unless the exhibit is specifically incorporated by
reference as an exhibit in this document. You can obtain documents incorporated
by reference as an exhibit in this document by requesting them in writing or by
telephone from the appropriate company at the following address:

<TABLE>
<S>                                             <C>
FOR STONE STOCKHOLDERS:                         FOR BASIN STOCKHOLDERS:
Stone Energy Corporation                        Basin Exploration, Inc.
625 East Kaliste Saloom Road                    1670 Broadway, Suite 2800
Lafayette, Louisiana 70508                      Denver, Colorado 80202
(337) 237-0410                                  (303) 685-8000
</TABLE>

     If you would like to request documents, please do so by           to
receive them before the special meetings. If you request any incorporated
documents from us, we will mail them to you by first class mail, or another
equally prompt means, within one business day after we receive your request.

     WE HAVE NOT AUTHORIZED ANYONE TO GIVE YOU ANY INFORMATION OR TO MAKE ANY
REPRESENTATION ABOUT THE MERGER OR OUR COMPANIES THAT DIFFERS FROM OR ADDS TO
THE INFORMATION CONTAINED IN THIS DOCUMENT OR IN THE DOCUMENTS OUR COMPANIES
HAVE PUBLICLY FILED WITH THE SEC. THEREFORE, IF ANYONE SHOULD GIVE YOU ANY
DIFFERENT OR ADDITIONAL INFORMATION, YOU SHOULD NOT RELY ON IT.

     IF YOU LIVE IN A JURISDICTION IN WHICH IT IS UNLAWFUL TO OFFER TO EXCHANGE
OR SELL, OR TO ASK FOR OFFERS TO EXCHANGE OR BUY, THE SECURITIES OFFERED BY THIS
DOCUMENT, OR TO ASK FOR PROXIES, OR IF YOU ARE A PERSON TO WHOM IT IS UNLAWFUL
TO DIRECT SUCH ACTIVITIES, THEN THE OFFER PRESENTED BY THIS DOCUMENT DOES NOT
EXTEND TO YOU.

     THE INFORMATION CONTAINED IN THIS DOCUMENT SPEAKS ONLY AS OF THE DATE
INDICATED ON THE COVER OF THIS DOCUMENT UNLESS THE INFORMATION SPECIFICALLY
INDICATES THAT ANOTHER DATE APPLIES.

                                       89







<PAGE>   98

                                                                         ANNEX A

                          AGREEMENT AND PLAN OF MERGER

                         DATED AS OF OCTOBER 28, 2000,
                                  BY AND AMONG

                            STONE ENERGY CORPORATION
                           PARTNER ACQUISITION CORP.
                                      AND
                            BASIN EXPLORATION, INC.
<PAGE>   99

                               TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                     PAGE
                                                                                     ----
<S>                   <C>                                                            <C>
AGREEMENT AND PLAN OF MERGER......................................................     1
ARTICLE I. THE MERGER.............................................................     1
SECTION 1.01          Effective Time Of The Merger................................     1
SECTION 1.02          Closing.....................................................     2
SECTION 1.03          Effects Of The Merger.......................................     2
SECTION 1.04          Directors And Officers......................................     2
ARTICLE II. CONVERSION OF SECURITIES..............................................     2
SECTION 2.01          Conversion Of Capital Stock.................................     2
SECTION 2.02          Exchange Of Certificates....................................     3
ARTICLE III. REPRESENTATIONS AND WARRANTIES OF COMPANY............................     6
SECTION 3.01          Organization Of Company.....................................     6
SECTION 3.02          Company Capital Structure...................................     6
SECTION 3.03          Authority; No Conflict; Required Filings And Consents.......     7
SECTION 3.04          SEC Filings; Financial Statements...........................     8
SECTION 3.05          No Undisclosed Liabilities; Suspense Accounts...............     9
SECTION 3.06          Absence Of Certain Changes Or Events........................     9
SECTION 3.07          Taxes.......................................................    10
SECTION 3.08          Properties..................................................    11
SECTION 3.09          Intellectual Property.......................................    12
SECTION 3.10          Contracts...................................................    12
SECTION 3.11          Investigations; Litigation..................................    13
SECTION 3.12          Environmental Matters.......................................    13
SECTION 3.13          Employee Benefit Plans......................................    14
SECTION 3.14          Compliance With Laws........................................    16
SECTION 3.15          Tax Matters.................................................    16
SECTION 3.16          Labor Matters...............................................    16
SECTION 3.17          Insurance...................................................    17
SECTION 3.18          No Existing Discussions.....................................    17
SECTION 3.19          Opinion Of Financial Advisor................................    17
SECTION 3.20          Section 203 Of The DGCL Not Applicable......................    17
SECTION 3.21          Oil And Gas Reserves........................................    17
SECTION 3.22          Take-Or-Pay Deliveries......................................    18
SECTION 3.23          Hedging.....................................................    18
SECTION 3.24          Required Vote of Company Stockholders.......................    18
ARTICLE IV. REPRESENTATIONS AND WARRANTIES OF PARTNER.............................    18
SECTION 4.01          Organization Of Partner And Merger Sub......................    18
SECTION 4.02          Partner Capital Structure...................................    19
SECTION 4.03          Authority; No Conflict; Required Filings And Consents.......    19
SECTION 4.04          SEC Filings; Financial Statements...........................    20
SECTION 4.05          No Undisclosed Liabilities; Suspense Accounts...............    21
SECTION 4.06          Absence Of Certain Changes Or Events........................    21
SECTION 4.07          Taxes.......................................................    22
SECTION 4.08          Properties..................................................    22
SECTION 4.09          Intellectual Property.......................................    23
SECTION 4.10          Contracts...................................................    23
SECTION 4.11          Investigations; Litigation..................................    24
SECTION 4.12          Environmental Matters.......................................    24
SECTION 4.13          Employee Benefit Plans......................................    25
</TABLE>

                                        i
<PAGE>   100

<TABLE>
<CAPTION>
                                                                                     PAGE
                                                                                     ----
<S>                   <C>                                                            <C>
SECTION 4.14          Compliance With Laws........................................    26
SECTION 4.15          Tax Matters.................................................    26
SECTION 4.16          Opinion Of Financial Advisor................................    26
SECTION 4.17          Oil And Gas Reserves........................................    26
SECTION 4.18          Take-Or-Pay Deliveries......................................    27
SECTION 4.19          Hedging.....................................................    27
SECTION 4.20          Required Vote of Partner Stockholders.......................    27
ARTICLE V. CONDUCT OF BUSINESS....................................................    27
SECTION 5.01          Covenants Of Company........................................    27
SECTION 5.02          Covenants Of Partner........................................    30
SECTION 5.03          Cooperation.................................................    30
ARTICLE VI. ADDITIONAL AGREEMENTS.................................................    30
SECTION 6.01          No Solicitation.............................................    30
SECTION 6.02          Joint Proxy Statement/Prospectus; Registration Statement....    31
SECTION 6.03          Quotation On Stock Exchanges................................    32
SECTION 6.04          Access To Information.......................................    32
SECTION 6.05          Stockholders Meetings.......................................    32
SECTION 6.06          Legal Conditions To Merger..................................    33
SECTION 6.07          Public Disclosure...........................................    34
SECTION 6.08          Tax-Free Reorganization.....................................    34
SECTION 6.09          Affiliate Agreements........................................    34
SECTION 6.10          New York Stock Exchange Quotation...........................    34
SECTION 6.11          Stock Plans.................................................    34
SECTION 6.12          Brokers Or Finders..........................................    36
SECTION 6.13          Indemnification.............................................    36
SECTION 6.14          Benefit Matters.............................................    36
SECTION 6.15          Registration Statement; Joint Proxy Statement/Prospectus....    38
SECTION 6.16          Pooling Accounting..........................................    39
ARTICLE VII. CONDITIONS TO MERGER.................................................    39
SECTION 7.01          Conditions To Each Party's Obligation To Effect The
                      Merger......................................................    39
SECTION 7.02          Additional Conditions To Obligations Of Partner And Merger
                      Sub.........................................................    40
SECTION 7.03          Additional Conditions To Obligations Of Company.............    40
ARTICLE VIII. TERMINATION AND AMENDMENT...........................................    41
SECTION 8.01          Termination.................................................    41
SECTION 8.02          Effect Of Termination.......................................    42
SECTION 8.03          Fees And Expenses...........................................    42
SECTION 8.04          Amendment...................................................    42
SECTION 8.05          Extension; Waiver...........................................    43
ARTICLE IX. MISCELLANEOUS.........................................................    43
SECTION 9.01          Nonsurvival Of Representations, Warranties And Agreements...    43
SECTION 9.02          Notices.....................................................    43
SECTION 9.03          Definitions.................................................    44
SECTION 9.04          Interpretation..............................................    44
SECTION 9.05          Counterparts................................................    45
SECTION 9.06          Entire Agreement; No Third Party Beneficiaries..............    45
SECTION 9.07          Governing Law...............................................    45
SECTION 9.08          Assignment..................................................    45
SECTION 9.09          Severability................................................    45
</TABLE>

                                       ii
<PAGE>   101

                             EXHIBITS AND APPENDIX

<TABLE>
<S>                   <C>
Exhibit A-1.........  Form of Company Voting Agreement
Exhibit A-2.........  Form of Partner Voting Agreement
Appendix 1.04(c)....  Non-Competition Term Sheet
</TABLE>

                                       iii
<PAGE>   102

                            TABLES OF DEFINED TERMS

<TABLE>
<CAPTION>
                                                               CROSS-REFERENCE
TERMS                                                           IN AGREEMENT
-----                                                          ---------------
<S>                                                            <C>
Acquisition Proposal........................................   Section 6.01
Affiliate...................................................   Section 6.09
Affiliate Agreement.........................................   Section 6.09
Agreement...................................................   Preamble
Bankruptcy and Equity Exception.............................   Section 3.03(a)
Certificate of Merger.......................................   Section 1.01
Closing.....................................................   Section 1.02
Closing Date................................................   Section 1.02
Company.....................................................   Preamble
Company Balance Sheet.......................................   Section 3.04(b)
Company Certificates........................................   Section 2.02(b)
Company Common Stock........................................   Section 2.01(b)
Company Disclosure Schedule.................................   Article III
Company Employee Plans......................................   Section 3.13(a)
Company Material Adverse Effect.............................   Section 9.03(a)
Company Material Contracts..................................   Section 3.10
Company Payout Balances.....................................   Section 3.21
Company Preferred Stock.....................................   Section 3.02(a)
Company Reserve Report......................................   Section 3.21
Company Stock Option........................................   Section 6.11(a)
Company SEC Reports.........................................   Section 3.04(a)
Company Stockholders' Meeting...............................   Section 6.15
Company Voting Agreements...................................   Preamble
Confidentiality Agreement...................................   Section 6.01
Continuing Employees........................................   Section 6.14(b)
Costs.......................................................   Section 6.13(a)
Current Premium.............................................   Section 6.13(b)
DGCL........................................................   Section 1.01
Effective Time..............................................   Section 1.01
Environmental Law...........................................   Section 3.12(b)
ERISA.......................................................   Section 3.13(a)
ERISA Affiliate.............................................   Section 3.13(a)
Exchange Act................................................   Section 3.03(c)
Exchange Agent..............................................   Section 2.02(a)
Exchange Fund...............................................   Section 2.02(a)
Exchange Ratio..............................................   Section 2.01(c)
Governmental Entity.........................................   Section 3.03(c)
Hazardous Substance.........................................   Section 3.12(c)
HSR Act.....................................................   Section 3.03(c)
Incentive Plan..............................................   Section 3.02(a)
Indemnified Parties.........................................   Section 6.13(a)
Internal Revenue Code.......................................   Preamble
IRS.........................................................   Section 3.07(b)
Joint Proxy Statement.......................................   Section 6.15
Liens.......................................................   Section 3.08
Litigation Matters..........................................   Section 3.11
Merger......................................................   Preamble
Order.......................................................   Section 6.06(b)
Outside Date................................................   Section 8.01(b)
</TABLE>

                                       iv
<PAGE>   103

<TABLE>
<CAPTION>
                                                               CROSS-REFERENCE
TERMS                                                           IN AGREEMENT
-----                                                          ---------------
<S>                                                            <C>
Partner.....................................................   Preamble
Partner Acquisition Proposal................................   Section 9.03(c)
Partner Balance Sheet.......................................   Section 4.04(b)
Partner Common Stock........................................   Section 2.01(b)
Partner Disclosure Schedule.................................   Article IV
Partner Employee Plans......................................   Section 4.13(a)
Partner Material Adverse Effect.............................   Section 9.03(b)
Partner Material Contracts..................................   Section 4.10
Partner Payout Balances.....................................   Section 4.21
Partner Preferred Stock.....................................   Section 4.02(a)
Partner Reserve Report......................................   Section 4.21
Partner SEC Reports.........................................   Section 4.04(a)
Partner Stock Plans.........................................   Section 4.02(a)
Partner Stockholders' Meeting...............................   Section 6.15
Partner Voting Agreements...................................   Preamble
Partner Voting Proposal.....................................   Section 6.05
Performance Share Plan......................................   Section 3.02(a)
Permits.....................................................   Section 3.14
Registration Statement......................................   Section 6.15
Retention Policy............................................   Section 3.06
Rights Agreement............................................   Section 3.02(a)
Rule 145....................................................   Section 6.09
SEC.........................................................   Section 3.03(c)
Securities Act..............................................   Section 3.04(a)
Subsidiary..................................................   Section 3.01
Superior Proposal...........................................   Section 6.01
Surviving Corporation.......................................   Section 1.03
Tax.........................................................   Section 3.07(a)
Taxes.......................................................   Section 3.07(a)
</TABLE>

                                        v
<PAGE>   104

                          AGREEMENT AND PLAN OF MERGER

     AGREEMENT AND PLAN OF MERGER (the "Agreement"), dated as of October 28,
2000, by and among Stone Energy Corporation, a Delaware corporation ("Partner"),
Partner Acquisition Corp., a Delaware corporation and a direct, wholly-owned
subsidiary of Partner ("Merger Sub"), and Basin Exploration, Inc., a Delaware
corporation ("Company").

     WHEREAS, the Boards of Directors of Partner and Company deem it advisable
and in the best interests of each corporation and its respective stockholders
that Partner and Company combine in order to advance the long-term business
interests of Partner and Company and each Board of Directors has recommended
that its respective stockholders approve the transactions contemplated hereby;

     WHEREAS, the combination of Partner and Company shall be effected by the
terms of this Agreement through a merger in which the stockholders of Company
will become stockholders of Partner (the "Merger");

     WHEREAS, as soon as practicable after the execution of this Agreement, as a
condition to the willingness of Partner to enter into this Agreement, the
members of the Board of Directors of Company, in their capacity as stockholders,
are entering into a Voting Agreement, dated as of the date hereof, with Partner,
a copy of which is attached to this Agreement as Exhibit A-1 (the "Company
Voting Agreement"), providing for, among other things, the agreement of such
stockholders to vote their respective shares of capital stock of Company in
favor of the approval and adoption of this Agreement and the Merger at the
Company Stockholders' Meeting (as defined herein);

     WHEREAS, as soon as practicable after the execution of this Agreement, as a
condition to the willingness of Company to enter into this Agreement, the
members of the Board of Directors of Partner, in their capacity as stockholders,
are entering into a Voting Agreement, dated as of the date hereof, with Company,
a copy of which is attached to this Agreement as Exhibit A-2 (the "Partner
Voting Agreement") providing for among other things, the agreement of such
stockholders to vote their respective shares of capital stock of Partner in
favor of any required amendment to Partner's certificate of incorporation and
the issuance of the shares of Partner Common Stock (as defined herein) in
connection with the Merger at the Partner Stockholders' Meeting (as defined
herein);

     WHEREAS, for federal income tax purposes, it is intended that the Merger
shall qualify as a reorganization within the meaning of Section 368(a) of the
Internal Revenue Code of 1986, as amended (the "Internal Revenue Code"); and

     WHEREAS, for accounting purposes, it is intended that the Merger shall be
accounted for as a pooling of interests.

     NOW, THEREFORE, in consideration of the foregoing and the respective
representations, warranties, covenants and agreements set forth below, the
parties agree as follows:

                                   ARTICLE I.

                                   THE MERGER

SECTION 1.01  Effective Time of the Merger.

     Subject to the provisions of this Agreement, a certificate of merger (the
"Certificate of Merger") in such form as is required by the relevant provisions
of the Delaware General Corporation Law (the "DGCL") shall be duly prepared,
executed and acknowledged by the Surviving Corporation (as defined in Section
1.03) and thereafter delivered to the Secretary of State of the State of
Delaware for filing, as provided in the DGCL, as early as practicable on the
Closing Date (as defined in Section 1.02). The Merger shall become effective
upon the filing of the Certificate of Merger with the Secretary of State of the
State of Delaware (the "Effective Time").
<PAGE>   105

SECTION 1.02  Closing.

     The closing of the Merger (the "Closing") will take place at 10:00 a.m.,
local time, on a date to be specified by Partner and Company, which shall be no
later than the second business day after satisfaction or waiver (as provided by
Section 8.05) of the latest to occur of the conditions set forth in Article
VII(other than those conditions that by their nature are to be satisfied at the
Closing, but subject to the fulfillment or waiver of those conditions) (the
"Closing Date"), at the offices of Brobeck, Phleger & Harrison LLP, Broomfield,
Colorado, unless another date, place or time is agreed to in writing by Partner
and Company.

SECTION 1.03  Effects of the Merger.

     At the Effective Time (i) the separate corporate existence of Merger Sub
shall cease and Merger Sub shall be merged with and into Company (Company
following the Merger is sometimes referred to below as the "Surviving
Corporation"), (ii) the Certificate of Incorporation of Merger Sub shall be
amended so that Article I of such Certificate of Incorporation reads in its
entirety as follows: "The name of the Corporation is Basin Exploration, Inc.,"
and, as so amended, such Certificate of Incorporation shall be the Certificate
of Incorporation of the Surviving Corporation, and (iii) the Bylaws of Merger
Sub as in effect immediately prior to the Effective Time shall be the Bylaws of
the Surviving Corporation.

     The Merger shall have the effects set forth in this Agreement and in the
applicable provisions of the DGCL. Without limiting the generality of the
foregoing, and subject thereto, at the Effective Time all the property, rights,
privileges, powers and franchises of Company and Merger Sub shall vest in the
Surviving Corporation, and all debts, liabilities and duties of Company and
Merger Sub shall become the debts, liabilities and duties of the Surviving
Corporation. As of the Effective Time, the Surviving Corporation shall be a
direct wholly-owned subsidiary of Partner.

SECTION 1.04  Directors and Officers.

     (a) The directors and officers of Merger Sub, immediately prior to the
Effective Time, shall be the initial officers and directors of the Surviving
Corporation, each to hold office in accordance with the Certificate of
Incorporation and Bylaws of the Surviving Corporation.

     (b) Partner shall take such action so that, upon the Effective Time,
Michael S. Smith shall become a member of Partner's Board of Directors as a
Class II Director whose term shall expire in 2001 (whereupon he will be
renominated by Partner as a Class II director for another term). Without
limiting the foregoing, if necessary to comply with this Section 1.04, Partner
shall cause the number of directors that shall constitute the Partner Board of
Directors to be increased by resolution of the Partner Board of Directors.

     (c) At or prior to the Effective Time, Partner shall, and Company shall use
its reasonable best efforts to cause Michael S. Smith to, enter into a
non-competition agreement, in form and substance reasonably satisfactory to
Partner and Michael S. Smith, reflecting the terms set forth on Appendix 1.04(c)
hereto, and which shall become effective as set forth therein.

                                  ARTICLE II.

                            CONVERSION OF SECURITIES

SECTION 2.01  Conversion of Capital Stock.

     As of the Effective Time, by virtue of the Merger and without any action on
the part of the holders of any shares of Company Common Stock (as defined in
Section 2.01(b)) or capital stock of Merger Sub:

          (a) Capital Stock of Merger Sub.  Each issued and outstanding share of
     the capital stock of Merger Sub shall be converted into and become one
     validly issued, fully paid and nonassessable share of Common Stock, par
     value $0.01 per share, of the Surviving Corporation.

                                        2
<PAGE>   106

          (b) Cancellation of Treasury Stock and Partner-Owned Stock.  All
     shares of Common Stock, par value $0.01 per share, of Company ("Company
     Common Stock") that are owned by Company as treasury stock and any shares
     of Company Common Stock owned by Partner, Merger Sub or any other
     wholly-owned Subsidiary (as defined in Section 3.01) of Partner or of
     Company shall be cancelled and retired and shall cease to exist and no
     stock of Partner or other consideration shall be delivered in exchange
     therefor. All shares of Common Stock, par value $0.01 per share, of Partner
     ("Partner Common Stock") owned by Company or any other holder thereof shall
     be unaffected by the Merger.

          (c) Exchange Ratio for Company Common Stock.  (i) Subject to Section
     2.02, each issued and outstanding share of Company Common Stock (other than
     shares to be cancelled in accordance with Section 2.01(b)) shall be
     converted into the right to receive .3974 of a share of Partner Common
     Stock (the "Exchange Ratio").

             (i) As of the Effective Time, all such shares of Company Common
        Stock shall no longer be outstanding and shall automatically be
        cancelled and retired and shall cease to exist, and each holder of a
        certificate or certificates that immediately prior to the Effective Time
        represented such shares shall cease to have any rights with respect
        thereto, except the right to receive the shares of Partner Common Stock
        and any cash in lieu of fractional shares of Partner Common Stock to be
        issued or paid in consideration therefor upon the surrender of such
        certificate in accordance with Section 2.02, without interest.

             (ii) If, between the date of this Agreement and the Effective Time,
        the outstanding shares of Company Common Stock or Partner Common Stock
        are changed into a different number or class of shares by reason of any
        stock split, division or subdivision of shares, stock dividend, reverse
        stock split, reclassification, recapitalization or other similar
        transaction, then the Exchange Ratio shall be appropriately adjusted to
        reflect the economic effects intended by this Section 2.01(c).

Section 2.02  Exchange of Certificates.

     The procedures for exchanging outstanding shares of Company Common Stock
for Partner Common Stock pursuant to the Merger are as follows:

          (a) Exchange Agent.  As of the Effective Time, Partner shall deposit
     with a bank or trust company designated by Partner and Company (the
     "Exchange Agent"), for the benefit of the holders of shares of Company
     Common Stock, for exchange in accordance with this Section 2.02, through
     the Exchange Agent, certificates representing the shares of Partner Common
     Stock (such shares of Partner Common Stock, together with any cash
     necessary to pay dividends or distributions with respect thereto and to
     make payments in lieu of any fractional shares as provided below, being
     hereinafter referred to as the "Exchange Fund") issuable pursuant to
     Section 2.01 in exchange for outstanding shares of Company Common Stock.

          (b) Exchange Procedures.  As soon as reasonably practicable after the
     Effective Time, the Exchange Agent shall mail to each holder of record of a
     certificate or certificates that immediately prior to the Effective Time
     represented outstanding shares of Company Common Stock (the "Company
     Certificates") whose shares were converted pursuant to Section 2.01 into
     the right to receive shares of Partner Common Stock plus cash in lieu of
     fractional shares, if any, of Partner Common Stock as provided below, (i) a
     letter of transmittal (which shall specify that delivery shall be effected,
     and risk of loss and title to the Company Certificates shall pass, only
     upon delivery of the Company Certificates to the Exchange Agent and shall
     be in such form and have such other provisions as Partner and Company may
     reasonably specify) and (ii) instructions for effecting the surrender of
     the Company Certificates in exchange for certificates representing shares
     of Partner Common Stock (plus cash in lieu of fractional shares, if any, of
     Partner Common Stock as provided below). Upon surrender of a Company
     Certificate for cancellation to the Exchange Agent or to such other agent
     or agents as may be appointed by Partner, together with such letter of
     transmittal, duly executed, the holder of such Company Certificate shall be
     entitled to receive in exchange therefor a certificate representing that
     number of whole shares of Partner Common Stock which such holder has the
     right to receive pursuant to the provisions of this Article II and
                                        3
<PAGE>   107

     cash in lieu of any fractional share of Partner Common Stock as provided
     below, and the Company Certificate so surrendered shall immediately be
     cancelled. In the event of a transfer of ownership of Company Common Stock
     that is not registered in the transfer records of Company, a certificate
     representing the proper number of shares of Partner Common Stock may be
     issued to a transferee if the Company Certificate representing such Company
     Common Stock is presented to the Exchange Agent, accompanied by all
     documents required to evidence and effect such transfer and by evidence
     that any applicable stock transfer taxes have been paid. Until surrendered
     as contemplated by this Section 2.02, each Company Certificate shall be
     deemed at any time after the Effective Time to represent only the right to
     receive upon such surrender the certificate representing shares of Partner
     Common Stock and cash, if any, in lieu of any fractional shares of Partner
     Common Stock as contemplated by this Section 2.02.  No interest will be
     paid or will accrue on any cash payable to holders of Company Certificates
     pursuant to the provisions of this Article II.

          (c) Distributions with Respect to Unexchanged Shares.  No dividends or
     other distributions declared or made after the Effective Time with respect
     to Partner Common Stock with a record date after the Effective Time shall
     be paid to the holder of any unsurrendered Company Certificate with respect
     to the shares of Partner Common Stock represented thereby and no cash
     payment in lieu of fractional shares shall be paid to any such holder
     pursuant to subsection (e) below until the holder of record of such Company
     Certificate shall surrender such Company Certificate. Subject to the effect
     of escheat or similar laws, following surrender of any such Company
     Certificate, there shall be paid to the record holder of the certificates
     representing whole shares of Partner Common Stock issued in exchange
     therefor, without interest, (i) at the time of such surrender, the amount
     of any cash payable in lieu of a fractional share of Partner Common Stock
     to which such holder is entitled pursuant to subsection (e) below and the
     amount of dividends or other distributions with a record date after the
     Effective Time previously paid with respect to such whole shares of Partner
     Common Stock, and (ii) at the appropriate payment date, the amount of
     dividends or other distributions with a record date after the Effective
     Time but prior to surrender and a payment date subsequent to surrender
     payable with respect to such whole shares of Partner Common Stock. Partner
     shall make available to the Exchange Agent, as needed, cash for these
     purposes.

          (d) No Further Ownership Rights in Company Common Stock.  All shares
     of Partner Common Stock issued upon the surrender for exchange of Company
     Certificates in accordance with the terms hereof (including any cash paid
     pursuant to subsection (c) or subsection (e) of this Section 2.02) shall be
     deemed to have been issued in full satisfaction of all rights pertaining to
     such shares of Company Common Stock, subject, however, to the Surviving
     Corporation's obligation to pay any dividends or make any other
     distributions with a record date prior to the Effective Time which may have
     been declared or made by Company on such shares of Company Common Stock in
     accordance with the terms of this Agreement (to the extent permitted under
     Section 5.01) prior to the date hereof and which remain unpaid at the
     Effective Time. At the Effective Time, holders of Company Certificates
     shall cease to have any rights as stockholders of Company, the stock
     transfer books of Company shall be closed with respect to all shares of
     Company Common Stock outstanding immediately prior to the Effective Time
     and from and after the Effective Time there shall be no further
     registration of transfers on the stock transfer books of the Surviving
     Corporation of the shares of Company Common Stock that were outstanding
     immediately prior to the Effective Time. If, after the Effective Time,
     Company Certificates are presented to the Surviving Corporation for any
     reason, they shall be cancelled and exchanged as provided in this Section
     2.02.

          (e) No Fractional Shares.  No certificate or scrip representing
     fractional shares of Partner Common Stock shall be issued upon the
     surrender for exchange of Company Certificates, no dividend or distribution
     of Partner shall relate to such fractional share interests, and such
     fractional share interests will not entitle the owner thereof to vote or to
     any other rights of a stockholder of Partner. Notwithstanding any other
     provision of this Agreement, each holder of shares of Company Common Stock
     exchanged pursuant to the Merger who would otherwise have been entitled to
     receive a fraction of a share of Partner Common Stock (after taking into
     account all Company Certificates delivered by such

                                        4
<PAGE>   108

     holder) shall receive, in lieu thereof, cash (without interest) in an
     amount equal to such fractional part of a share of Partner Common Stock
     multiplied by the average of the last reported sales prices of Partner
     Common Stock, as reported on the New York Stock Exchange Transaction Tape
     (as reported in The Wall Street Journal, or if not reported thereby, any
     other authoritative source) on each of the ten (10) trading days
     immediately preceding the date of the Effective Time.

          (f) Termination of Exchange Fund.  Any portion of the Exchange Fund
     that remains undistributed to the holders of Company Certificates for one
     hundred eighty (180) days after the Effective Time shall be delivered to
     Partner, upon demand, and any stockholders of Company who have not
     previously complied with this Section 2.02 shall thereafter look only to
     Partner for payment of their claim for Partner Common Stock, any cash in
     lieu of fractional shares of Partner Common Stock and any dividends or
     distributions with respect to Partner Common Stock.

          (g) No Liability.  None of Partner, Company, Merger Sub or the
     Exchange Agent shall be liable to any person in respect of any shares of
     Partner Common Stock or Company Common Stock, as the case may be, for such
     shares (or dividends or distributions with respect thereto) or cash from
     the Exchange Fund in each case delivered to a public official pursuant to
     any applicable abandoned property, escheat or similar law. If any Company
     Certificate shall not have been surrendered prior to seven years after the
     Effective Time (or immediately prior to such earlier date on which the
     shares of Partner Common Stock represented by such Company Certificate
     would otherwise escheat to or become the property of any governmental body
     or authority), any such shares of Partner Common Stock, or cash, dividends
     or distributions in respect of such Company Certificate shall, to the
     extent permitted by applicable law, become the property of Partner, free
     and clear of all claims or interest of any person previously entitled
     thereto.

          (h) Withholding Rights.  Each of Partner and the Surviving Corporation
     shall be entitled to deduct and withhold from the consideration otherwise
     payable pursuant to this Agreement to any holder of shares of Company
     Common Stock such amounts as it is required to deduct and withhold with
     respect to the making of such payment under the Internal Revenue Code and
     the rules and regulations promulgated thereunder, or any provision of
     state, local or foreign tax law. To the extent that amounts are so withheld
     by the Surviving Corporation or Partner, as the case may be, such withheld
     amounts shall be treated for all purposes of this Agreement as having been
     paid to the holder of the shares of Company Common Stock in respect of
     which such deduction and withholding was made by the Surviving Corporation
     or Partner, as the case may be.

          (i) Lost Company Certificates.  If any Company Certificate shall have
     been lost, stolen or destroyed, upon the making of an affidavit of that
     fact by the person claiming such Company Certificate to be lost, stolen or
     destroyed and, if required by the Surviving Corporation, the posting by
     such person of a bond in such reasonable amount as the Surviving
     Corporation may direct as indemnity against any claim that may be made
     against it with respect to such Company Certificate, the Exchange Agent
     will issue in exchange for such lost, stolen or destroyed Company
     Certificate the shares of Partner Common Stock and any cash in lieu of
     fractional shares, and unpaid dividends and distributions on shares of
     Partner Common Stock deliverable in respect thereof pursuant to this
     Agreement.

          (j) Affiliates.  Notwithstanding anything herein to the contrary,
     Company Certificates surrendered for exchange by any Affiliate (as defined
     in Section 6.09) of Company shall not be exchanged until Partner has
     received an Affiliate Agreement (as defined in Section 6.09) from such
     Affiliate.

          (k) Tax Consequences.  For federal income tax purposes, the Merger is
     intended to constitute a reorganization within the meaning of Section
     368(a) of the Internal Revenue Code. The parties to this Agreement hereby
     adopt this Agreement as a "plan of reorganization" within the meaning of
     Sections 1.368-2(g) and 1.368-3(a) of the United States Treasury
     Regulations.

          (l) Accounting Treatment.  For accounting purposes, the Merger is
     intended to be treated as a pooling of interests.

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<PAGE>   109

          (m) Investment of Exchange Fund.  The Exchange Agent shall invest any
     cash included in the Exchange Fund, as directed by Partner, on a daily
     basis. Any interest and other income resulting from such investments shall
     be paid to Partner.

          (n) Further Assurances.  At and after the Effective Time, the officers
     and directors of the Surviving Corporation shall be authorized to execute
     and deliver, in the name and on behalf of Company or Merger Sub, any deeds,
     bills or sale, assignments or assurances and to take and do, in the name
     and on behalf of Company or Merger Sub, any other actions and things
     reasonably required to vest, perfect or confirm of record or otherwise in
     the Surviving Corporation any and all rights, title and interest in, to and
     under any of the rights, properties or assets acquired or to be acquired by
     the Surviving Corporation as a result of or in connection with, the Merger.

                                  ARTICLE III.

                   REPRESENTATIONS AND WARRANTIES OF COMPANY

     Company represents and warrants to Partner that the statements contained in
this Article III are true and correct, except as set forth herein or in the
disclosure schedule delivered by Company to Partner and Merger Sub on or before
the date of this Agreement (the "Company Disclosure Schedule"). The Company
Disclosure Schedule shall be arranged in paragraphs corresponding to the
numbered and lettered sections contained in this Agreement and the disclosure in
any paragraph shall qualify other sections in this Agreement only to the extent
that it is reasonably apparent from a reading of such disclosure that it also
qualifies or applies to such other sections.

SECTION 3.01  Organization of Company.

     Each of Company and its Subsidiaries is a corporation duly organized,
validly existing and in good standing under the laws of the jurisdiction of its
incorporation, has all requisite corporate power and authority to own, lease and
operate its property and to carry on its business as now being conducted and as
proposed to be conducted, and is duly qualified to do business and is in good
standing as a foreign corporation in each jurisdiction in which the failure to
be so qualified would have a Company Material Adverse Effect (as defined in
Section 9.03(a)). The copies of Company's certificate of incorporation and
by-laws attached to the Company Disclosure Schedule are complete and correct and
in full force and effect on the date hereof. Neither Company nor any of its
Subsidiaries is in violation of any of the provisions of its organizational
documents. Except as set forth in the Company SEC Reports (as defined in Section
3.04(a)) filed prior to the date hereof, neither Company nor any of its
Subsidiaries directly or indirectly owns any equity or similar interest in, or
any interest convertible into or exchangeable or exercisable for, any
corporation, partnership, joint venture or other business association or entity,
excluding securities in any publicly traded company held for investment by
Company and comprising less than five percent (5%) of the outstanding stock of
such company and any interests owned by Company in oil and gas properties
pursuant to joint operating, participation or similar type agreements. As used
in this Agreement, the word "Subsidiary" means, with respect to any party, any
corporation or other organization, whether incorporated or unincorporated, of
which (i) such party or any other Subsidiary of such party is a general partner
(excluding partnerships, the general partnership interests of which held by such
party or any Subsidiary of such party do not have a majority of the voting
interest in such partnership) or (ii) at least a majority of the securities or
other interests having by their terms ordinary voting power to elect a majority
of the Board of Directors or others performing similar functions with respect to
such corporation or other organization is directly or indirectly owned or
controlled by such party or by any one or more of its Subsidiaries, or by such
party and one or more of its Subsidiaries.

SECTION 3.02  Company Capital Structure.

     (a) The authorized capital stock of Company consists of 50,000,000 shares
of Common Stock, $0.01 par value, and 10,000,000 shares of Preferred Stock,
$0.01 par value ("Company Preferred Stock"). As of October 6, 2000, (i)
18,516,390 shares of Company Common Stock were issued and outstanding, all of
which are validly issued, fully paid, nonassessable and not subject to any
statutory or contractual preemptive rights
                                        6
<PAGE>   110

(which total includes all shares of Company Common Stock issued as restricted
shares pursuant to the Incentive Plan described below or pursuant to outstanding
share awards under Company's Performance Share Plan described below) and (ii) no
shares of Company Common Stock were held in the treasury of Company or by its
Subsidiaries. The Company Disclosure Schedule shows the number of shares of
Company Common Stock reserved for future issuance pursuant to stock options
granted and outstanding as of October 6, 2000 under Company's Equity Incentive
Plan (the "Incentive Plan"), including the name of the holder of each option,
the number of shares of Company Common Stock subject to each such option, the
vesting schedule and exercise price per share and the maximum term of that
option. The Company Disclosure Schedule also indicates the number of shares of
Company Common Stock issued as restricted stock or pursuant to outstanding share
awards under Company's Performance Share Plan (the "Performance Share Plan") and
the applicable service requirements or performance milestones for earning those
shares. No material change in such capitalization has occurred between October
6, 2000 and the date of this Agreement. As of the date of this Agreement, none
of the shares of Company Preferred Stock is issued and outstanding. All shares
of Company Common Stock subject to issuance as specified above are duly
authorized and, upon issuance on the terms and conditions specified in the
instruments pursuant to which they are issuable, shall be validly issued, fully
paid and nonassessable. Except as set forth in the Incentive Plan or in the
Rights Agreement dated February 24, 1996, as amended (the "Rights Agreement"),
or, with respect to events occurring after the date hereof, to the extent
permitted by Section 5.01, there are no obligations, contingent or otherwise, of
Company or any Subsidiary to issue, transfer, sell, repurchase, redeem or
otherwise acquire any shares of capital stock or other voting security of
Company or the capital stock of any Subsidiary or to provide funds to or make
any material investment (in the form of a loan, capital contribution or
otherwise) in any such Subsidiary or any other entity other than guarantees of
bank obligations of Subsidiaries entered into in the ordinary course of
business. All of the outstanding shares of, capital stock of, or other ownership
interests in, each of Company's Subsidiaries are duly authorized, validly
issued, fully paid and nonassessable and all such shares are owned by Company
free and clear of all security interests, liens, claims, pledges, agreements,
limitations in Company's voting rights, charges or other encumbrances of any
nature.

     (b) Except as set forth in this Section 3.02 or as reserved for future
grants of options under the Incentive Plan, or, with respect to events occurring
after the date hereof, to the extent permitted by Section 5.01, there are no
equity securities of any class of Company or any of its Subsidiaries, or any
security exchangeable into or exercisable for such equity securities, issued,
reserved for issuance or outstanding. Except as set forth in this Section 3.02
or the Incentive Plan, or, with respect to events occurring after the date
hereof, to the extent permitted by Section 5.01, there are no outstanding
subscriptions, options, rights, warrants, convertible securities, stock
appreciation rights, phantom equity, calls, rights, commitments or agreements of
any character to which Company or any of its Subsidiaries is a party or by which
it is bound obligating Company or any of its Subsidiaries to issue, deliver or
sell, or cause to be issued, delivered or sold, additional shares of capital
stock of Company or any of its Subsidiaries or obligating Company or any its
Subsidiaries to grant, extend, accelerate the vesting of or enter into or make
payment with respect to any such subscription, option, right, warrant,
convertible security, stock appreciation right, phantom equity, call, right,
commitment or agreement. To the best knowledge of Company, there are no voting
trusts, proxies or other voting agreements or understandings with respect to the
shares of capital stock of Company.

SECTION 3.03  Authority; No Conflict; Required Filings and Consents.

     (a) Company has all requisite corporate power and authority to enter into
this Agreement and to consummate the transactions contemplated by this
Agreement. The execution and delivery of this Agreement and the consummation of
the transactions contemplated by this Agreement by Company have been duly and
validly authorized by all necessary corporate action on the part of Company,
subject only to the approval of the Merger by Company's stockholders under the
DGCL. This Agreement has been duly executed and delivered by Company and
constitutes a valid and binding obligation of Company, enforceable in accordance
with its terms, subject to bankruptcy, insolvency, fraudulent transfer,
reorganization, moratorium and similar laws of general applicability relating to
or affecting creditors' rights and to general principles of equity (the
"Bankruptcy and Equity Exception").

                                        7
<PAGE>   111

     (b) The execution and delivery of this Agreement by Company does not, and
the consummation of the transactions contemplated by this Agreement will not,
(i) conflict with, or result in any violation or breach of, any provision of the
Certificate of Incorporation or Bylaws of Company, (ii) assuming that those of
the consents contemplated by Section 3.03(c) of this Agreement, the failure of
which to obtain, individually or in the aggregate, would not have a Company
Material Adverse Effect, are obtained, result in any violation or breach of, or
constitute (with or without notice or lapse of time, or both) a default under,
or give rise to a penalty or right of termination, cancellation or acceleration
of any obligation or loss of any material benefit under, or to increased,
additional, accelerated or guaranteed rights or entitlements of any person or
entity under (including the receipt of any consideration), or require a consent
or waiver under, any of the terms, conditions or provisions of any note, bond,
mortgage, indenture, lease, contract (including, without limitation, any Company
Material Contract) or other agreement, instrument or obligation to which Company
or any of its Subsidiaries is a party or by which any of them or any of their
properties or assets may be bound, or (iii) assuming the consents contemplated
by Section 3.03(c) of this Agreement are obtained, conflict with or violate any
Permit (as defined in Section 3.14 below), judgment, order, decree, statute,
law, ordinance, rule or regulation applicable to Company or any of its
Subsidiaries or any of its or their properties or assets, except in the case of
(ii) and (iii) for any such conflicts, violations, breaches, defaults,
terminations, cancellations or accelerations that, individually or in the
aggregate, would not be reasonably likely to have a Company Material Adverse
Effect. Section 3.03(b) of the Company Disclosure Schedule sets forth a correct
and complete list of the Company Material Contracts (as defined in Section 3.10)
under which consents, waivers or notifications are required prior to the
consummation of the transactions contemplated by this Agreement, which have not
previously been obtained.

     (c) No consent, approval, order or authorization of, or registration,
declaration or filing with, any court, administrative agency or commission or
other governmental authority or instrumentality, domestic or foreign,
("Governmental Entity") is required by or with respect to Company in connection
with the execution and delivery of this Agreement or the consummation of the
transactions contemplated hereby, except for (i) the filing of the pre-merger
notification report under the Hart-Scott-Rodino Antitrust Improvements Act of
1976, as amended ("HSR Act"), (ii) the filing of the Certificate of Merger with
the Delaware Secretary of State, (iii) the filing of the Joint Proxy Statement
(as defined in Section 6.15 below) with the Securities and Exchange Commission
(the "SEC") in accordance with the Securities Exchange Act of 1934, as amended
(the "Exchange Act"), (iv) such consents, approvals, orders, authorizations,
registrations, declarations and filings as may be required under applicable
state securities laws and the laws of any foreign country, (v) such governmental
or tribal consents, qualifications or filings as are customarily obtained or
made following the transfer of interests in oil and gas property interests and
(vi) such other consents, authorizations, filings, approvals and registrations
that, if not obtained or made, would not be reasonably likely to have a Company
Material Adverse Effect.

SECTION 3.04  SEC Filings; Financial Statements.

     (a) Company has made available to Partner true and complete copies of each
registration statement (other than registration statements on Form S-8), report,
proxy statement or information statement (other than preliminary materials)
filed by Company with the SEC since December 31, 1998, each in the form
(including exhibits and any amendments thereto) filed with the SEC prior to the
date hereof (collectively, the "Company SEC Reports"), and Company has timely
filed all forms, reports and documents required to be filed by it with the SEC
pursuant to relevant securities statutes, regulations, policies and rules since
such time. The Company SEC Reports (i) at the time filed, complied in all
material respects with the applicable requirements of the Securities Act of
1933, as amended (the "Securities Act"), the Exchange Act, and the rules and
regulations thereunder, as the case may be, and (ii) did not at the time they
were filed (or if amended or superseded by a filing prior to the date of this
Agreement, then as and on the date so amended or superseded) contain any untrue
statement of a material fact or omit to state a material fact required to be
stated in such Company SEC Reports or necessary in order to make the statements
in such Company SEC Reports, in the light of the circumstances under which they
were made, not misleading. None of Company's Subsidiaries is subject to the
periodic reporting requirements of the Exchange Act or is otherwise required to
file any forms, reports or other documents with the SEC.
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<PAGE>   112

     (b) Each of the consolidated financial statements (including, in each case,
any related notes) contained in the Company SEC Reports complied as to form in
all material respects with the applicable published rules and regulations of the
SEC with respect thereto, was prepared in accordance with generally accepted
accounting principles applied on a consistent basis throughout the periods
involved (except as may be indicated in the notes to such financial statements
or, in the case of unaudited statements, as permitted by Form 10-Q of the SEC)
and fairly presented the consolidated financial position of Company and its
Subsidiaries as of the dates and the consolidated results of its operations and
cash flows for the periods indicated, except that the unaudited interim
financial statements are subject to normal and recurring year-end adjustments.
The unaudited balance sheet of Company as of June 30, 2000 is referred to herein
as the "Company Balance Sheet."

SECTION 3.05  No Undisclosed Liabilities; Suspense Accounts.

     Except as disclosed in the Company SEC Reports filed and publicly available
prior to the date hereof and except for abandonment obligations related to
Company's oil and gas properties which are estimated in the Reserve Report
(described in Section 3.21), Company and its Subsidiaries do not have any
obligations or liabilities, whether or not accrued, contingent or otherwise,
that individually or in the aggregate would reasonably be likely to have a
Company Material Adverse Effect. The Company Balance Sheet reflects all suspense
accounts owed by Company as of the date hereof, except as would not reasonably
be expected to have a Company Material Adverse Effect.

SECTION 3.06  Absence of Certain Changes or Events.

     Except as disclosed in the Company SEC Reports filed and publicly available
prior to the date hereof, since December 31, 1999, Company and its Subsidiaries
have conducted their businesses in all material respects only in the ordinary
course and in a manner consistent with past practice, and, since such date,
there has not been (i) any material change by Company and its Subsidiaries, when
taken as a whole, in their accounting methods, principles or practices to which
Partner has not previously consented in writing; (ii) any declaration, setting
aside, or payment of any dividend or other distribution in respect of the
capital stock of Company; (iii) any split, combination or reclassification of
any of Company's capital stock or any issuance or the authorization of any
issuance of any other securities in respect of, in lieu of or in substitution
for shares of Company's capital stock (other than under the Incentive Plan or
the Performance Share Plan); (iv) any event, occurrence, development or state of
circumstances or facts that has had, or would be reasonably likely to have, a
Company Material Adverse Effect; provided, however, that for purposes of this
Section 3.06(iv), the effects of (A) any aggregate decrease during any period of
20 consecutive days in the average daily quantity of oil, gas and other gaseous
and liquid hydrocarbons ("Hydrocarbons") being produced by Company and its
Subsidiaries, taken as a whole, that is less than 30% of the average of the net
daily production of such Hydrocarbons by the Company and its Subsidiaries, taken
as a whole, during the 20-day period ending with the date of this Agreement or
that is caused by mechanical difficulties, surface equipment, pipeline
curtailments or events of force majeure, and (B) any aggregate net decrease in
the proved Hydrocarbon reserves of Company and its Subsidiaries, taken as a
whole (excluding, for the purpose of determining the amount of any such
decrease, any decrease due to depletion resulting from production or due to
changes in oil and gas prices, and including any increase due to discoveries or
additions) that is less than 20% of the amount of the Company's proved reserves
set forth in the Company Reserve Report, shall not be considered in determining
whether a Company Material Adverse Effect has occurred or is reasonably likely
to occur, provided further, that any disagreement over the extent of any such
reserve decrease shall be resolved by prompt submittal to an independent
reservoir engineer reasonably acceptable to both parties whose decision shall be
binding and shall be delivered no later than five business days following
submittal; (v) (A) any granting by Company or any of its Subsidiaries to any
current or former director, executive officer or other employee of Company or
its Subsidiaries of any increase in compensation, bonus or other benefits,
except for, with respect to any events occurring prior to the date hereof,
normal increases in base compensation or bonuses in the ordinary course of
business consistent with past practice and set forth on Section 3.06 of the
Company Disclosure Schedule and, with respect to events occurring after the date
hereof, as permitted by Section 5.01 or as was required under any employment
agreements in effect as of the date of the most recent
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audited financial statements included in the Company SEC Reports filed and
publicly available prior to the date hereof, (B) any granting by Company or any
of its Subsidiaries to any such current or former director, executive officer or
employee of any increase in severance or termination pay, (C) any entry by
Company or any of its Subsidiaries into, or any amendments of, any employment,
deferred compensation, consulting, severance, termination or indemnification
agreement with any current or former director, executive officer or employee, or
(D) any amendment to, or modification of, any Company stock option or Company
warrant; (vi) any tax election or any settlement of any income tax liability or
tax attributes that individually or in the aggregate is reasonably likely to
adversely affect the tax liability or tax attributes of Company or any of its
Subsidiaries in any material respect or any settlement or compromise of any
material income tax liability; (vii) any incurrence of indebtedness for money
borrowed by Company or any of its Subsidiaries other than debt incurred in the
ordinary course of business in a manner consistent with past practice; (viii)
any creation of a material lien, security interest or any other encumbrance,
howsoever arising, in respect of or over any of the material assets of Company
or any of its Subsidiaries; (ix) other than, with respect to acquisitions or
dispositions occurring after the date hereof, as would be permitted by Section
5.01, any material acquisition or disposition of assets by Company or any of its
Subsidiaries, including the sale, lease, farm-out, license or other disposition
of any material properties or assets, except for (A) sales of Hydrocarbons in
the ordinary course of business, (B) acquisitions or dispositions set forth in
Section 3.06 of the Company Disclosure Schedule, (C) dispositions of interests
in exploratory prospects in exchange for interests in other prospects from third
parties which Company in good faith believes to have an equivalent value,
consistent with past practices, (D) sales of equipment and/or replacements
thereof in the ordinary course of business, and (E) acquisitions of leases at
the Central Gulf of Mexico lease sale in March 2000, provided, however, that the
exceptions set forth in clauses (A) through (E) above shall not be applicable to
any acquisitions of assets from, or dispositions of assets to, any third parties
in which, to Company's knowledge, any officer or director of Company has,
directly or indirectly, any existing or prospective equity or other ownership
interest or any other arrangement or understanding having the same economic
effect, other than with respect to any company that is publicly traded on a
national securities market or exchange, to the extent such ownership interest is
less than two percent (2%) of such publicly traded company; (x) any
modification, assignment, termination or relinquishment of rights under any
Company Material Contract by Company or any of its Subsidiaries other than such
modification, assignment, termination or relinquishment in the ordinary course
of business consistent with past practice; (xi) any damage, destruction or
casualty loss, whether or not covered by insurance, that individually or in the
aggregate would be reasonably likely to have a Company Material Adverse Effect
(it being understood that the availability of any insurance coverage shall be
taken into account in determining whether such damage, destruction or loss would
be reasonably likely to have a Company Material Adverse Effect); or (xii) any
making of a loan or an advance by Company or any of its Subsidiaries not in the
ordinary course of business.

SECTION 3.07  Taxes.

     (a) For the purposes of this Agreement, the terms "Tax" and, collectively,
"Taxes" mean any and all material federal, state, local and foreign taxes,
assessments and other governmental charges, duties, impositions and liabilities,
including taxes based upon or measured by gross receipts, income, profits,
sales, use and occupation, and value added, ad valorem, transfer, gains,
franchise, withholding, payroll, recapture, employment, excise, unemployment
insurance, social security, business license, occupation, business organization,
stamp and property taxes, together with all interest, penalties and additions
imposed with respect to such amounts and any obligations under any agreements or
arrangements with any other person with respect to such amounts and including
any liability for taxes of a predecessor entity.

     (b) Except as would not be reasonably likely, individually or in the
aggregate, to have a Company Material Adverse Effect, (i) Company and each of
its Subsidiaries have, or prior to the Closing Date will have, (A) filed all
federal, state, local and foreign tax returns and reports required to be filed
by them prior to the date of this Agreement (taking into account extensions),
(B) paid or accrued all Taxes due and payable with respect to the periods
covered by such tax returns and reports or otherwise due and payable on or prior
to the Closing Date and (C) paid or accrued all Taxes for which a notice of
assessment or collection has been received (other than amounts being contested
in good faith by appropriate proceedings), (ii) neither the
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Internal Revenue Service (the "IRS") nor any other taxing authority has asserted
or proposed in writing any claim or adjustment relating to Taxes, or to the
actual knowledge of the executive officers of Company, is threatening to assert
any claims for Taxes, (iii) Company and each of its Subsidiaries have withheld
or collected and paid over to the appropriate governmental authorities (or are
properly holding for such payment) all Taxes required by law to be withheld or
collected, and (iv) there are no liens for Taxes upon the assets of Company or
any of its Subsidiaries (other than liens for Taxes that are not yet due or that
are being contested in good faith by appropriate proceedings).

     (c) To Company's knowledge, there exists no claim by a Tax authority in a
jurisdiction where any of Company and its Subsidiaries does not file Tax returns
that it is or may be subject to taxation in that jurisdiction. There are no Tax
allocation or sharing agreements or arrangements affecting any of Company and
its Subsidiaries. No payments are due or will become due by any of Company and
its Subsidiaries pursuant to any such agreement or arrangement or any tax
indemnification agreement. Neither Company nor any of its Subsidiaries will be
required to include any amount in income for any taxable period beginning after
December 31, 1999 as a result of a change in accounting or pursuant to any
agreement with any Tax authority with respect to any prior taxable period.
Neither Company nor any of its Subsidiaries (i) has been a member of an
affiliated group filing a consolidated federal income Tax return (other than a
group the common parent of which was Company) or (ii) has any liability for the
Taxes of any person or entity (other than any of Company and its Subsidiaries)
under Treasury Regulation Section 1.1502-6 (or any similar provision of state,
local or foreign law), as a transferee or successor, by contract, or otherwise.
Neither Company nor any of its Subsidiaries have entered into any agreement or
arrangement with any Tax authority that requires any of Company and its
Subsidiaries to take any action or to refrain from taking any action.

SECTION 3.08  Properties.

     (a) Except for goods and other property sold, used or otherwise disposed of
since June 30, 2000 in the ordinary course of business, Company and its
Subsidiaries have Good and Marketable Title (as defined below), for oil and gas
purposes, in and to all federal leases covering acreage offshore in the Gulf of
Mexico and to all the proved reserves reflected in the Company Reserve Report
(as defined in Section 3.21) as owned by Company and its Subsidiaries, and
defensible title for oil and gas purposes to all other properties, interests in
properties and assets, real and personal, reflected in the Company Balance Sheet
as owned by Company and its Subsidiaries, free and clear of any liens, security
interests, charges, mortgages or other encumbrances of any kind (collectively
"Liens"), except: (i) Liens associated with obligations reflected in the Company
Reserve Report or the Company Balance Sheet; (ii) Liens for current taxes not
yet due and payable, (iii) materialman's, mechanic's, repairman's, employee's,
contractor's, operator's, and other similar liens, charges or encumbrances
arising in the ordinary course of business (A) if they have not been perfected
pursuant to law, (B) if perfected, they have not yet become due and payable or
payment is being withheld as provided by law, or (C) if their validity is being
contested in good faith by appropriate action, (iv) all rights to consent by,
required notices to, filings with, or other actions by governmental entities in
connection with the sale or conveyance of oil and gas leases or interests if
they are customarily obtained subsequent to the sale or conveyance, and (v) such
imperfections of title, easements and Liens as would not reasonably be expected
to have, individually or in the aggregate, a Company Material Adverse Effect.
All leases and other agreements pursuant to which Company or any of its
Subsidiaries leases or otherwise acquires or obtains operating rights affecting
any real or personal property are in good standing, valid and effective and all
royalties, rentals and other payments due by the Company to any lessor of any
such oil and gas leases have been paid, except in each case, as would not,
individually or in the aggregate, reasonably be expected to have a Company
Material Adverse Effect. All major items of operating equipment of Company and
its Subsidiaries are in good operating condition and in a state of reasonable
maintenance and repair, ordinary wear and tear excepted, except as would not,
individually or in the aggregate, reasonably be expected to have a Company
Material Adverse Effect.

     (b) The term "Good and Marketable Title" shall, for purposes of this
Section 3.08, with respect to Company and its Subsidiaries, mean such title
that: (1) is deducible of record (from the records of the applicable parish or
county or (A) in the case of federal leases, from the records of the applicable
office of the

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<PAGE>   115

Minerals Management Service or Bureau of Land Management, (B) in the case of
Indian leases, from the applicable office of the Bureau of Indian Affairs, (C)
in the case of state leases, from the records of the applicable state land
office) or is assignable to Company or its Subsidiaries out of an interest of
record (as so defined) by reason of the performance by Company or its
Subsidiaries of all operations required to earn an enforceable right to such
assignment; (2) is free from reasonable doubt to the end that a prudent
purchaser engaged in the business of the ownership, development and operation of
producing oil and gas properties with knowledge of all of the facts and their
legal bearing would be willing to accept and pay full value for the same and a
prudent lender would be willing to lend against it as collateral without
discount for title matters; (3) entitles Company or its Subsidiaries to receive
not less than the interest set forth in the Company Reserve Report with respect
to each proved property evaluated therein under the caption "Net Revenue
Interest" or "NRI" without reduction during the life of such property except as
stated in the Company Reserve Report; (4) obligates Company or its Subsidiaries
to pay costs and expenses relating to each such proved property in an amount not
greater than the interest set forth under the caption "Working Interest" or "WI"
in the Company Reserve Report with respect to such property without increase
over the life of such property except as shown on the Company Reserve Report;
and (5) does not restrict the ability of Company or its Subsidiaries to utilize
the properties as currently intended.

SECTION 3.09  Intellectual Property.

     Each of Company and its Subsidiaries owns, or is licensed or otherwise
possesses legally enforceable rights to use, all trademarks, trade names,
patents, service marks, copyrights, and any applications for such trademarks,
trade names, patents, service marks and copyrights, know-how, computer software
programs or applications and tangible or intangible proprietary information or
material ("Intellectual Property") that are necessary to conduct the business of
Company and its Subsidiaries as currently conducted, including without
limitation, any seismic data or information used by Company and its
Subsidiaries, subject to such exceptions that, individually or in the aggregate,
would not be reasonably likely to have a Company Material Adverse Effect.
Section 3.09 of the Company Disclosure Schedule sets forth a list of each
material agreement pursuant to which Company or its Subsidiaries licenses or has
the right to use or acquire Intellectual Property (including, without
limitation, seismic data or information). No person or entity has notified
either Company or any of its Subsidiaries that their use of the Intellectual
Property infringes on the rights of any person or entity, subject to such claims
and infringements as do not, individually or in the aggregate, give rise to any
liability on the part of Company and its Subsidiaries that would be reasonably
likely to have a Company Material Adverse Effect, and to Company's knowledge, no
person is infringing on any right of Company or any of its Subsidiaries with
respect to any such Intellectual Property. No claims are pending or, to
Company's knowledge, threatened that Company or any of its Subsidiaries is
infringing upon the rights of any person or entity with regard to any
Intellectual Property that, individually or in the aggregate, would be
reasonably likely to have a Company Material Adverse Effect.

SECTION 3.10  Contracts.

     (a) Set forth in Section 3.10 of the Company Disclosure Schedule is a list
of each contract, lease, indenture, agreement, arrangement or understanding to
which Company or any of its Subsidiaries is a party or subject that would be
required to be included as an exhibit to a Form S-1 Registration Statement
pursuant to the rules and regulations of the SEC if such a registration
statement were to be filed by the Company on the date hereof and no previous
filings had been made (collectively, the "Company Material Contracts").

     (b) Except for such matters that, individually or in the aggregate, would
not be reasonably expected to have a Company Material Adverse Effect, with
respect to the Company Material Contracts, (A) all Company Material Contracts
are in full force and effect and are the valid and legally binding obligations
of Company or the Subsidiary party thereto, and to Company's knowledge, the
legally binding obligations of the other parties thereto, and are enforceable in
accordance with their respective terms, subject to the Bankruptcy and Equity
Exception; (B) Company or the Subsidiary party thereto is not in breach or
default (nor does there exist any condition which upon the passage of time or
the giving of notice or both would reasonably be expected to cause such a breach
or default) with respect to, and to the knowledge of Company, no other party to
any

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Company Material Contract is in breach or default with respect to, its
obligations thereunder, including with respect to payments or otherwise; and (C)
no party to any Company Material Contract has given written notice to Company or
the Subsidiary party thereto of any action to terminate, cancel, rescind or
procure a judicial reformation thereof.

SECTION 3.11  Investigations; Litigation.

     Section 3.11 of the Company Disclosure Schedule sets forth a list of all
pending Litigation Matters (as defined below). Except as described in the
Company SEC Reports filed prior to the date hereof or pursuant to the pre-merger
notification process under the HSR Act with respect to this transaction (i) no
investigation or review by any Governmental Entity with respect to Company or
any of its Subsidiaries or any of the transactions contemplated by this
Agreement is pending, nor to Company's knowledge has any Governmental Entity
(foreign or domestic) indicated an intention to conduct the same, (ii) there is
no action, suit or proceeding, claim, arbitration or investigation ("Litigation
Matter") against Company or any of its Subsidiaries pending or, to Company's
knowledge, threatened, and (iii) there are no outstanding orders, rulings,
injunctions, awards, decrees, judgments or stipulations by or with any court or
administrative agency or by arbitration, that in the case of each of (i), (ii)
and (iii) above, individually or in the aggregate, if determined adversely to
Company or any of its Subsidiaries, would have a Company Material Adverse Effect
or would materially impair or delay the ability of Company to consummate the
transactions contemplated by this Agreement.

SECTION 3.12  Environmental Matters.

     (a) Except as disclosed in the Company SEC Reports filed and publicly
available prior to the date hereof and, in case of clauses (i)-(iv) and
(viii)-(ix) and (xi), except for such matters that, individually or in the
aggregate, are not reasonably likely to have a Company Material Adverse Effect:
(i) Company and its Subsidiaries have complied with all applicable Environmental
Laws (as defined in Section 3.12(b)) and, to the knowledge of Company, there are
no facts or circumstances that could reasonably be expected to prevent or
preclude future compliance with all applicable Environmental Laws; (ii) the
properties currently owned or operated by Company and its Subsidiaries
(including soils, groundwater, surface water, buildings or other structures) are
not contaminated with any Hazardous Substances (as defined in Section 3.12(c));
(iii) to the knowledge of Company, the properties formerly owned or operated by
Company or any of its Subsidiaries were not contaminated with Hazardous
Substances during the period of ownership or operation by Company or any of its
Subsidiaries; (iv) Company's and its Subsidiaries' properties have been used by
Company and its Subsidiaries solely for oil and gas exploration, production,
processing, transportation and related operations and to its knowledge have not
been used, whether by Company, its Subsidiaries or any other person or entity,
for the generation, storage or disposal of a Hazardous Substance (other than
those substances lawfully used and contained in oil and gas operations) or as a
landfill or other waste disposal site; (v) neither Company nor any of its
Subsidiaries, within the five years immediately preceding the date hereof, has
received any written notice, demand, letter, claim or request for information
alleging that Company or any of its Subsidiaries may be in violation of or
liable under any Environmental Law; (vi) neither Company nor any of its
Subsidiaries is subject to any orders, decrees, injunctions or other
arrangements with any Governmental Entity or (except for indemnities under
purchase and sale agreements, operating agreements, farm-out agreements or other
similar agreements, whereby Company or any of its Subsidiaries has acquired,
disposed of, or operated oil and gas properties, as to which (A) no existing
claim is pending or to its knowledge threatened against Company or any of its
Subsidiaries and (B) Company is not aware of any facts or circumstances that
could reasonably be expected to form the basis for a claim) is subject to any
indemnity or other agreement with any third party relating to liability under
any Environmental Law or relating to Hazardous Substances, including without
limitation any arrangements that require any change in the present condition or
operation of any of its properties in order to comply with conditions or
restrictions that relate to the protection of the environment; (vii) there are
no actions, suits, claims or proceedings seeking money damages, injunctive
relief, remedial action or other remedy pending or, to Company's knowledge,
threatened against Company or its Subsidiaries relating to the violation of, or
noncompliance with, an Environmental Law; the disposal, discharge, or release of
any Hazardous Substance; or the exposure of any person to any other solid waste,
pollutant, chemical
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<PAGE>   117

substance, noise or vibration; (viii) each of Company and its Subsidiaries has
obtained all permits, licenses and other authorizations which are required under
Environmental Laws for the conduct of its existing drilling and development
operations and is in compliance with all terms and conditions of such permits,
licenses and authorizations; (ix) all necessary applications, inspection
reports, certificates and other instruments pertaining to Environmental Laws on
properties operated by Company or any of its Subsidiaries have been filed with
the appropriate Governmental Entity; (x) neither the execution of this Agreement
nor the consummation of the transactions contemplated by this Agreement will
violate any Environmental Law or require the consent or approval of any agency
charged with enforcing any Environmental Law, which violation or the failure to
obtain such consent or approval would materially impair or delay the ability of
Company to consummate the transactions contemplated by this Agreement; and (xi)
there are no circumstances or conditions involving Company or any of its
Subsidiaries that could reasonably be expected to result in any claims,
liability, investigations, costs or restrictions on the ownership, use or
transfer of any property of Company pursuant to any Environmental Law.

     (b) As used herein, the term "Environmental Law" means any federal, state,
local or foreign law, regulation, order, decree, permit, authorization, opinion,
common law or agency requirement relating to: (i) the protection, investigation
or restoration of the environment, health and safety, or natural resources, (ii)
the handling, use, presence, disposal, release or threatened release of any
Hazardous Substance or (iii) noise, odor, wetlands, pollution, contamination or
any injury or threat of injury to persons or property, including, but not
limited to, the federal Comprehensive Environmental Response, Compensation, and
Liability Act, the Resource Conservation and Recovery Act, the Clean Water Act,
the Clean Air Act, the Safe Drinking Water Act, the Toxic Substance Control Act,
the Hazardous Materials Transportation Act, the Hazardous Materials
Transportation Act, the Oil Pollution Act of 1990, and all state statutes
serving similar or related purposes.

     (c) As used herein, the term "Hazardous Substance" means any substance that
is: (i) listed, classified or regulated as a "hazardous substance," "toxic
substance," "hazardous material," or "solid waste" pursuant to any Environmental
Law; (ii) any petroleum product or by-product, asbestos-containing material,
lead-containing paint or plumbing, polychlorinated biphenyls, radioactive
materials or radon; (iii) any chemical substance, (A) which is toxic, explosive,
corrosive, flammable, infectious, radioactive, carcinogenic, mutagenic, or
otherwise hazardous and is regulated by any Governmental Entity, (B) the
presence of which at any property owned by a party causes a nuisance upon such
location or to adjacent properties or poses a hazard to the health or safety of
persons at or about such property, or (C) the presence of which on adjacent
properties constitutes a trespass by a party's business; or (iv) any other
substance which is the subject of regulatory action by any Governmental Entity
pursuant to any Environmental Law or the presence of which requires
investigation or remediation thereunder. Hazardous Substances does not include
Naturally Occurring Radioactive Material which may be found in Company's oil and
gas wells and related well equipment. The term "Hazardous Substance" shall not
include crude oil or drilling mud or drilling fluids used in the exploration,
development or production of oil or natural gas.

SECTION 3.13  Employee Benefit Plans.

     (a) Company has listed in Section 3.13(a) of the Company Disclosure
Schedule, and has provided to Partner complete and correct copies of, all
employee benefit plans (as defined in Section 3(3) of the Employee Retirement
Income Security Act of 1974, as amended ("ERISA")) and all bonus, stock option,
stock purchase, incentive, deferred compensation, supplemental retirement,
severance, and other similar employee benefit plans (including, without
limitation, the retention and severance plan and program thereunder adopted by
Company for its non-executive officer employees (the "Retention Policy")),
written or otherwise, for the benefit of, or relating to, any current or former
employee or other service provider of Company, any Subsidiary of Company or any
trade or business (whether or not incorporated) which is treated as a single
employer with Company or any Subsidiary of Company (an "ERISA Affiliate") within
the meaning of Section 414(b), (c), (m) or (o) of the Internal Revenue Code
(together, the "Company Employee Plans").

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<PAGE>   118

     (b) With respect to each Company Employee Plan, Company has made available
to Partner, a true and correct copy of (i) the most recent annual report (Form
5500) filed with the IRS for each Company Employee Plan with respect to which
such report is required to be filed, (ii) each trust agreement and group annuity
contract or insurance policy, if any, relating to such Company Employee Plan,
(iii) the most current favorable determination letter received from the IRS as
to the qualified status under the Internal Revenue Code of each Company Employee
Plan subject to Section 401 of the Internal Revenue Code, and (iv) the most
recent summary plan description for each Company Employee Plan required to have
such a summary plan description. None of Company, any Subsidiary of Company or
any ERISA Affiliate sponsors, maintains or contributes to, nor has any such
entity at any time within six years preceding the date of this Agreement
sponsored, maintained or contributed to, any plan that is subject to Title IV of
ERISA (including without limitation a multiemployer plan within the meaning of
Section 3(37) of ERISA), Section 302 of ERISA or Section 412 of the Internal
Revenue Code. Each Company Employee Plan intended to be qualified under Section
401 of the Internal Revenue Code has been administered and maintained in all
material respects in accordance with its terms and all applicable laws,
including ERISA and the Internal Revenue Code, and, except as set forth in
Section 3.13(b) of the Company Disclosure Schedule, each such plan has received
a favorable determination letter from the Internal Revenue Service regarding
such qualified status. Except as set forth in Section 3.13(b) of the Company
Disclosure Schedule, there has been no termination or partial termination of any
such plan within the meaning of Section 411(d)(3) of the Internal Revenue Code.
Affected participants were fully vested in their plan accounts as required under
Section 411(d)(3) of the Internal Revenue Code in connection with the partial
termination described in Section 3.13(b) of the Company Disclosure Schedule.
There are no actions, suits or claims pending (other than routine claims for
benefits) or, to Company's knowledge, threatened against, or with respect to,
any of the Company Employee Plans or their assets. There is no matter pending
(other than routine qualification determination filings) with respect to any of
the Company Employee Plans before any Governmental Entity.

     (c) With respect to the Company Employee Plans, individually and in the
aggregate, no event has occurred, and to the knowledge of Company, there exists
no condition or set of circumstances in connection with which Company could be
subject to any material liability under ERISA, the Internal Revenue Code or any
other applicable law.

     (d) With respect to the Company Employee Plans, individually and in the
aggregate, there are no funded benefit obligations for which contributions have
not been made or properly accrued and there are no unfunded benefit obligations
which have not been accounted for by reserves, or otherwise properly footnoted
in accordance with generally accepted accounting principles, on the financial
statements of Company, which obligations are reasonably likely to have a Company
Material Adverse Effect.

     (e) Except as disclosed in the Company SEC Reports filed prior to the date
of this Agreement, and except as provided for in this Agreement, neither Company
nor any of its Subsidiaries is a party to any oral or written (i) agreement with
any officer or other key employee of Company or any of its Subsidiaries, the
benefits of which are contingent, or the terms of which are materially altered,
upon the occurrence of a transaction involving Company of the nature
contemplated by this Agreement, (ii) agreement with any officer of Company
providing any term of employment or compensation guarantee, or (iii) agreement
or plan, including any stock option plan, stock appreciation right plan,
restricted stock plan or stock purchase plan, any of the benefits of which will
be increased, or the vesting of the benefits of which will be accelerated, by
the occurrence of any of the transactions contemplated by this Agreement or the
value of any of the benefits of which will be calculated on the basis of any of
the transactions contemplated by this Agreement.

     (f) Except as set forth in Section 3.13(f) of the Company Disclosure
Schedule, and based on the assumptions set forth therein (which assumptions
represent the best currently available estimates of Company after consultation
with its accountants as to the matters covered thereby, it being understood that
the actual calculation may differ from the assumed amounts), in connection with
the consummation of the transactions contemplated by this Agreement, no payments
of money or other property, acceleration of benefits, or provisions of other
rights have or will be made hereunder, under any agreement contemplated herein,
under any agreement described in Section 3.13(e) or Section 3.16(e)(determined
without regard to whether such agreement is terminable by Company, without
material cost to Company, with no more than 30 days notice)
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<PAGE>   119

or under the Company Employee Plans that would be reasonably likely to result in
imposition of the sanctions imposed under Sections 280G and 4999 of the Internal
Revenue Code, whether or not some other subsequent action or event would be
required to cause such payment, acceleration, or provision to be triggered.
Partner represents and warrants that nothing has come to Partner's attention as
of the date hereof that causes Partner to believe that Section 3.13(f) of the
Company Disclosure Schedule is incorrect.

SECTION 3.14  Compliance With Laws.

     Neither Company nor any of its Subsidiaries is in violation or default of,
or has received any notices of violation or default with respect to, any
applicable federal, state, local or foreign statute, law, rule, order, decree or
regulation, including without limitation, any filing or reporting requirement
thereunder with respect to the conduct of its business, or the ownership or
operation of its business, except for violations or defaults that, individually
or in the aggregate, are not reasonably likely to have a Company Material
Adverse Effect. Each of Company and its Subsidiaries has all licenses,
franchises, permits, authorizations, approvals, plans, surveys and environmental
impact reports ("Permits") legally required to enable it to carry on its
business as currently carried on and such Permits are all in full force and
effect and no proceeding is pending and neither Company nor any of its
Subsidiaries has received any written notice of any action seeking the
revocation or limitation of or is in default or violation of, any such Permit,
except in each case as would not reasonably be expected to have a Company
Material Adverse Effect; provided, however, that notwithstanding the foregoing,
no representation or warranty in this Section 3.14 is made with respect to
Permits issued pursuant to Environmental Laws, which are covered exclusively by
the provisions set forth in Section 3.12, or with respect to Permits to conduct
exploratory operations which have not been commenced as of the date of this
Agreement.

SECTION 3.15  Tax Matters.

     To its knowledge, after consulting with its Tax counsel, neither Company
nor any of its Affiliates (as defined in Section 6.09) has taken or agreed to
take any action that would prevent the Merger from constituting a transaction
qualifying as a reorganization under Section 368(a) of the Internal Revenue
Code.

SECTION 3.16  Labor Matters.

     (a) Neither Company nor any of its Subsidiaries is a party to or otherwise
bound by any collective bargaining agreement, contract or other agreement or
understanding with a labor union or labor organization, nor, as of the date
hereof, is Company or any of its Subsidiaries the subject of any material
proceeding asserting that Company or any of its Subsidiaries has committed an
unfair labor practice or is seeking to compel it to bargain with any labor union
or labor organization nor, as of the date of this Agreement, is there pending
or, to the knowledge of the executive officers of Company, threatened, any
material labor strike, dispute, walkout, work stoppage, slow-down or lockout
involving Company or any of its Subsidiaries.

     (b) Neither Company nor any of its Subsidiaries has any knowledge of any
current union organizing activities among the employees of Company or any of its
Subsidiaries, nor does any question concerning representation exist concerning
such employees.

     (c) Company and its Subsidiaries are and have been in compliance with all
applicable laws respecting employment and employment practices (including
without limitation with respect to discrimination and harassment) and all laws,
ordinances and regulations respecting the terms and conditions of employment,
except as would not reasonably be expected to have a Company Material Adverse
Effect.

     (d) Neither the Company nor any of its Subsidiaries is in violation of the
Worker Adjustment and Retraining Notification Act of 1988 (the "WARN Act"), or
any similar state or local law, in each case that would reasonably be expected
to have a Company Material Adverse Effect.

     (e) Company has listed in Section 3.16 of the Company Disclosure Schedule,
and has provided to Partner complete and correct copies of, all employment and
consulting agreements with any current or former employees or consultants
currently in effect to which Company or any of its Subsidiaries is a party and
that are

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not terminable in Company's sole discretion, without material cost to Company,
with no more than 30 days notice.

SECTION 3.17  Insurance.

     Company and its Subsidiaries maintain insurance coverage with reputable
companies, reasonably adequate for the operation of their business and
consistent in all material respects with industry practice, including without
limitation, as to amounts and types of coverage.

SECTION 3.18 No Existing Discussions.

     As of the date of this Agreement, Company has ceased, and has instructed
its directors, officers, financial advisors, representatives, employees and
agents to cease, all direct and indirect discussions and negotiations with any
other party that were ongoing immediately prior to the date hereof with respect
to an Acquisition Proposal (as defined in Section 6.01).

SECTION 3.19 Opinion of Financial Advisor.

     The financial advisor of Company, Goldman, Sachs & Co., has delivered to
Company an opinion dated the date of this Agreement to the effect that, based
upon and subject to the matters set forth therein, the Exchange Ratio is fair to
the holders of Company Common Stock from a financial point of view. Company has
delivered, or will deliver promptly after receipt of such written opinion, a
copy of such written opinion to Partner.

SECTION 3.20 Section 203 of the DGCL Not Applicable.

     Company and its Board of Directors have each taken all action required to
be taken by it in order to exempt the execution, delivery or performance of this
Agreement by Company, the consummation of the Merger by Company and the
transactions contemplated hereby from, and this Agreement, the Merger and the
transactions contemplated hereby are exempt from, the restrictions contained in
Section 203 of the DGCL applicable to a "business combination" (as defined in
Section 203). No other "fair price," "moratorium," "control share acquisition"
or other similar anti-takeover statute or regulation is applicable to Company or
(by reason of Company's participation therein) the Merger or the other
transactions contemplated by this Agreement. Company and its Board of Directors
have each taken all action required to be taken by it in order to exempt Partner
from the status of an "Acquiring Person" under the Rights Plan and to ensure
that no stock acquisition date, distribution date or triggering event shall
occur by reason of the execution of this Agreement or the consummation of the
Merger.

SECTION 3.21 Oil and Gas Reserves.

     Company has furnished Partner the Company's estimates of Company's and its
Subsidiaries' oil and gas reserves as of June 30, 2000 in a report as described
in Section 3.21 of the Company Disclosure Schedule (the "Company Reserve
Report"). Except as would not reasonably be expected to have a Company Material
Adverse Effect, the factual, non-interpretive data on which the Company Reserve
Report was based for purposes of estimating the oil and gas reserves set forth
in the Company Reserve Report and in any supplement thereto or update thereof
furnished to Partner was accurate and incorporates the following: the interests
owned by Company and its Subsidiaries at the time the Company Reserve Report was
prepared, the cost of operating the properties, all production and cost data
adjusted for all oil and/or gas imbalances due, all tests and operations on
Company's and its Subsidiaries' properties of which Company was aware at the
time the Company Reserve Report was prepared and all capital costs reasonably
expected by Company at such time to be necessary to operate, develop and plug
and abandon the properties described therein. To the best knowledge of Company,
and based on the information given to Company by third-party operators for all
wells not operated by Company, the Company Payout Balances (as defined below)
for each of the wells as used in the Company Reserve Report were accurate as of
the dates to which Company had calculated them, except as would not reasonably
be expected to have a Company Material Adverse Effect. "Company Payout Balances"

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<PAGE>   121

means the status, as of the dates of Company's calculations, of the recovery by
Company or a third party of a cost amount specified in the contract relating to
a well out of the revenue from such well where the net revenue interest of
Company therein will be reduced or increased when such amount has been
recovered.

SECTION 3.22 Take-or-Pay Deliveries.

     Except as would not, individually or in the aggregate, reasonably be
expected to have a Company Material Adverse Effect, there are no calls
(exclusive of market calls) on Company's oil or gas production and Company has
no obligation to deliver oil or gas pursuant to any take-or-pay, prepayment or
similar arrangement without receiving full payment therefor. Section 3.22 of the
Company Disclosure Schedule sets forth the Company's estimates of its imbalances
in gas production as of September 30, 2000. The Company does not have any other
imbalances in gas production that, individually or in the aggregate, would be
reasonably likely to have a Company Material Adverse Effect.

SECTION 3.23 Hedging.

     Company has set forth in Section 3.23 of the Company Disclosure Schedule a
summary of Company's position with respect to its futures, hedge, swap, collar,
put, call, floor, cap, option or other contracts that are intended to benefit
from, relate to or reduce or eliminate the risk of fluctuations in the price of
commodities, including Hydrocarbons, or securities (collectively, "Hedges") as
of the date hereof. Except as set forth in Section 3.23 of the Company
Disclosure Schedule, neither Company nor any of its Subsidiaries is bound by any
Hedges as of the date hereof.

SECTION 3.24 Required Vote of Company Stockholders.

     The affirmative vote of the holders of a majority of the outstanding shares
of Company Common Stock is required to approve the Merger. No other vote of the
stockholders of Company is required by law, the certificate of incorporation or
by-laws of Company or otherwise in order for Company to consummate the Merger
and the transactions contemplated thereby.

                                  ARTICLE IV.

                   REPRESENTATIONS AND WARRANTIES OF PARTNER

     Partner represents and warrants to Company that the statements contained in
this Article IV are true and correct, except as set forth in the disclosure
schedule delivered by Partner to Company and Merger Sub on or before the date of
this Agreement (the "Partner Disclosure Schedule"). The Partner Disclosure
Schedule shall be arranged in paragraphs corresponding to the numbered and
lettered sections contained in this Agreement and the disclosure in any
paragraph shall qualify other sections in this Agreement only to the extent that
it is reasonably apparent from a reading of such disclosure that it also
qualifies or applies to such other sections.

SECTION 4.01 Organization of Partner and Merger Sub.

     Each of Partner and its Subsidiaries is a corporation duly organized,
validly existing and in good standing under the laws of the jurisdiction of its
incorporation, has all requisite corporate power and authority to own, lease and
operate its property and to carry on its business as now being conducted and as
proposed to be conducted, and is duly qualified to do business and is in good
standing as a foreign corporation in each jurisdiction in which the failure to
be so qualified would have a Partner Material Adverse Effect (as defined in
Section 9.03(b)). The copies of Partner's certificate of incorporation and
by-laws attached to the Partner Disclosure Schedule are complete and correct and
in full force and effect on the date hereof. Neither Partner nor any of its
Subsidiaries is in violation of any of the provisions of its organizational
documents. Except as set forth in the Partner SEC Reports (as defined in Section
4.04(a)) filed prior to the date hereof, neither Partner nor any of its
Subsidiaries directly or indirectly owns any equity or similar interest in, or
any interest convertible into or exchangeable or exercisable for, any
corporation, partnership, joint venture or other

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<PAGE>   122

business association or entity, excluding securities in any publicly traded
company held for investment by Partner and comprising less than five percent
(5%) of the outstanding stock of such company and any interests owned by Partner
in oil and gas properties pursuant to joint operating, participation or similar
type agreements.

SECTION 4.02  Partner Capital Structure.

     (a) The authorized capital stock of Partner consists of 25,000,000 shares
of Common Stock, $0.01 par value, and 5,000,000 shares of Preferred Stock, $0.01
par value ("Partner Preferred Stock"). As of October 27, 2000, (i) 18,515,725
shares of Partner Common Stock were issued and outstanding, all of which are
validly issued, fully paid, nonassessable and not subject to any statutory or
contractual preemptive rights and (ii) no shares of Partner Common Stock were
held in the treasury of Partner or by its Subsidiaries. The Partner Disclosure
Schedule shows the number of shares of Partner Common Stock reserved for future
issuance pursuant to stock options granted and outstanding as of October 27,
2000, under Partner's 2000 Amended and Restated Stock Option Plan and Partner's
1993 Non-employee Directors Stock Option Plan (collectively, the "Partner Stock
Plans"), and the plans under which such options were granted. No material change
in such capitalization has occurred between October 27, 2000 and the date of
this Agreement. As of the date of this Agreement, none of the shares of Partner
Preferred Stock is issued and outstanding. All shares of Partner Common Stock
subject to issuance as specified above are duly authorized and, upon issuance on
the terms and conditions specified in the instruments pursuant to which they are
issuable, shall be validly issued, fully paid and nonassessable. Except as set
forth in the Partner Stock Plans or in the Rights Agreement dated October 15,
1998 (the "Rights Agreement"), or, with respect to events occurring after the
date hereof, to the extent permitted by Section 5.02, there are no obligations,
contingent or otherwise, of Partner or any Subsidiary to issue, transfer, sell,
repurchase, redeem or otherwise acquire any shares of capital stock or other
voting security of Partner or the capital stock of any Subsidiary or to provide
funds to or make any material investment (in the form of a loan, capital
contribution or otherwise) in any such Subsidiary or any other entity other than
guarantees of bank obligations of Subsidiaries entered into in the ordinary
course of business. All of the outstanding shares of, capital stock of, or other
ownership interests in, each of Partner's Subsidiaries are duly authorized,
validly issued, fully paid and nonassessable and all such shares are owned by
Partner free and clear of all security interests, liens, claims, pledges,
agreements, limitations in Partner's voting rights, charges or other
encumbrances of any nature.

     (b) Except as set forth in this Section 4.02 or as reserved for future
grants of options under the Partner Stock Plans, or, with respect to events
occurring after the date hereof, to the extent permitted by Section 5.02, there
are no equity securities of any class of Partner or any of its Subsidiaries, or
any security exchangeable into or exercisable for such equity securities,
issued, reserved for issuance or outstanding. Except as set forth in this
Section 4.02, the Partner Stock Plans, awards granted under the Partner Stock
Plans, and Partner's 401(k) Profit Sharing Plan, as of the date hereof, there
are no outstanding subscriptions, options, rights, warrants, convertible
securities, stock appreciation rights, phantom equity, calls, rights,
commitments or agreements of any character to which Partner or any of its
Subsidiaries is a party or by which it is bound obligating Partner or any of its
Subsidiaries to issue, deliver or sell, or cause to be issued, delivered or
sold, additional shares of capital stock of Partner or any of its Subsidiaries
or obligating Partner or any its Subsidiaries to grant, extend, accelerate the
vesting of or enter into or make payment with respect to any such subscription,
option, right, warrant, convertible security, stock appreciation right, phantom
equity, call, right, commitment or agreement. To the best knowledge of Partner,
there are no voting trusts, proxies or other voting agreements or understandings
with respect to the shares of capital stock of Partner.

SECTION 4.03  Authority; No Conflict; Required Filings and Consents.

     (a) Each of Partner and Merger Sub has all requisite corporate power and
authority to enter into this Agreement and to consummate the transactions
contemplated by this Agreement. The execution and delivery of this Agreement and
the consummation of the transactions contemplated by this Agreement by Partner
and Merger Sub have been duly and validly authorized by all necessary corporate
action on the part of each of Partner and Merger Sub (including the approval of
the Merger by Partner as the sole stockholder of Merger Sub), subject only to
the approval of the Partner Voting Proposal (as defined in Section 6.05) by
Partner's

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<PAGE>   123

stockholders. This Agreement has been duly executed and delivered by each of
Partner and Merger Sub and constitutes a valid and binding obligation of each of
Partner and Merger Sub, enforceable in accordance with its terms, subject to the
Bankruptcy and Equity Exception.

     (b) The execution and delivery of this Agreement by Partner and Merger Sub
does not, and the consummation of the transactions contemplated by this
Agreement will not, (i) conflict with, or result in any violation or breach of,
any provision of the Certificate of Incorporation or Bylaws of Partner or Merger
Sub, (ii) result in any violation or breach of, or constitute (with or without
notice or lapse of time, or both) a default under, or give rise to a penalty or
right of termination, cancellation or acceleration of any obligation or loss of
any material benefit under, or to increased, additional, accelerated or
guaranteed rights or entitlements of any person or entity under (including the
receipt of any consideration), or require a consent or waiver under, any of the
terms, conditions or provisions of any note, bond, mortgage, indenture, lease,
contract (including, without limitation, any Partner Material Contract) or other
agreement, instrument or obligation to which Partner or any of its Subsidiaries
is a party or by which any of them or any of their properties or assets may be
bound, or (iii) assuming the consents contemplated by Section 4.03(c) of this
Agreement are obtained, conflict with or violate any Permit, judgment, order,
decree, statute, law, ordinance, rule or regulation applicable to Partner or any
of its Subsidiaries or any of its or their properties or assets, except in the
case of (ii) and (iii) for any such conflicts, violations, breaches, defaults,
terminations, cancellations or accelerations that, individually or in the
aggregate, would not be reasonably likely to have a Partner Material Adverse
Effect. Section 4.03(b) of the Partner Disclosure Schedule sets forth a correct
and complete list of the Partner Material Contracts (as defined in Section 4.10)
under which consents, waivers or notifications are required prior to the
consummation of the transactions contemplated by this Agreement, which have not
previously been obtained.

     (c) No consent, approval, order or authorization of, or registration,
declaration or filing with, any Governmental Entity is required by or with
respect to Partner in connection with the execution and delivery of this
Agreement or the consummation of the transactions contemplated hereby, except
for (i) the filing of the pre-merger notification report under the HSR Act, (ii)
the filing of the Certificate of Merger with the Delaware Secretary of State,
(iii) the filing of the Registration Statement (as defined in Section 6.15
below) with the SEC in accordance with the Securities Act, (iv) the filing of
the Joint Proxy Statement with the SEC in accordance with the Exchange Act, (v)
such consents, approvals, orders, authorizations, registrations, declarations
and filings as may be required under applicable state securities laws and the
laws of any foreign country, (vi) such governmental or tribal consents,
qualifications or filings as are customarily obtained or made following the
transfer of interests in oil and gas property interests and (vii) such other
consents, authorizations, filings, approvals and registrations that, if not
obtained or made, would not be reasonably likely to have a Partner Material
Adverse Effect.

SECTION 4.04  SEC Filings; Financial Statements.

     (a) Partner has made available to Company true and complete copies of each
registration statement (other than registration statements on Form S-8), report,
proxy statement or information statement (other than preliminary materials)
filed by Partner with the SEC since December 31, 1998, each in the form
(including exhibits and any amendments thereto) filed with the SEC prior to the
date hereof (collectively, the "Partner SEC Reports"), and Partner has timely
filed all forms, reports and documents required to be filed by it with the SEC
pursuant to relevant securities statutes, regulations, policies and rules since
such time. The Partner SEC Reports (i) at the time filed, complied in all
material respects with the applicable requirements of the Securities Act, the
Exchange Act, and the rules and regulations thereunder, as the case may be, and
(ii) did not at the time they were filed (or if amended or superseded by a
filing prior to the date of this Agreement, then as and on the date so amended
or superseded) contain any untrue statement of a material fact or omit to state
a material fact required to be stated in such Partner SEC Reports or necessary
in order to make the statements in such Partner SEC Reports, in the light of the
circumstances under which they were made, not misleading. None of Partner's
Subsidiaries is subject to the periodic reporting requirements of the Exchange
Act or is otherwise required to file any forms, reports or other documents with
the SEC.

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     (b) Each of the consolidated financial statements (including, in each case,
any related notes) contained in the Partner SEC Reports complied as to form in
all material respects with the applicable published rules and regulations of the
SEC with respect thereto, was prepared in accordance with generally accepted
accounting principles applied on a consistent basis throughout the periods
involved (except as may be indicated in the notes to such financial statements
or, in the case of unaudited statements, as permitted by Form 10-Q of the SEC)
and fairly presented the consolidated financial position of Partner and its
Subsidiaries as of the dates and the consolidated results of its operations and
cash flows for the periods indicated, except that the unaudited interim
financial statements are subject to normal and recurring year-end adjustments.
The unaudited balance sheet of Partner as of June 30, 2000 is referred to herein
as the "Partner Balance Sheet."

SECTION 4.05  No Undisclosed Liabilities; Suspense Accounts.

     Except as disclosed in the Partner SEC Reports filed and publicly available
prior to the date hereof and except for abandonment obligations related to
Partner's oil and gas properties that are estimated in the Partner Reserve
Report (described in Section 4.17), Partner and its Subsidiaries do not have any
obligations or liabilities, whether or not accrued, contingent or otherwise,
that individually or in the aggregate would reasonably be likely to have a
Partner Material Adverse Effect. The Partner Balance Sheet reflects all suspense
accounts and gas balancing obligations owed by Partner as of the date hereof,
except as would not reasonably be expected to have a Partner Material Adverse
Effect.

SECTION 4.06  Absence Of Certain Changes Or Events.

     Except as disclosed in the Partner SEC Reports filed and publicly available
prior to the date hereof, since December 31, 1999, Partner and its Subsidiaries
have conducted their businesses in all material respects only in the ordinary
course and in a manner consistent with past practice, and, since such date,
there has not been (i) any material change by Partner and its Subsidiaries, when
taken as a whole, in their accounting methods, principles or practices to which
Company has not previously consented in writing; (ii) any declaration, setting
aside, or payment of any dividend or other distribution in respect of the
capital stock of Partner; (iii) any split, combination or reclassification of
any of Partner's capital stock or any issuance or the authorization of any
issuance of any other securities in respect of, in lieu of or in substitution
for shares of Partner's capital stock; (iv) any event, occurrence, development
or state of circumstances or facts that has had, or would be reasonably likely
to have, a Partner Material Adverse Effect; provided, however, that for purposes
of this Section 4.06(iv), the effects of (A) any aggregate decrease during any
period of 20 consecutive days in the average daily quantity of oil, gas and
other gaseous and liquid hydrocarbons ("Hydrocarbons") being produced by Partner
and its Subsidiaries, taken as a whole, that is less than 30% of the average of
the net daily production of such Hydrocarbons by the Partner and its
Subsidiaries, taken as a whole, during the 20-day period ending with the date of
this Agreement or that is caused by mechanical difficulties, surface equipment,
pipeline curtailments or events of force majeure, and (B) any aggregate net
decrease in the proved Hydrocarbon reserves of Partner and its Subsidiaries,
taken as a whole (excluding, for the purpose of determining the amount of any
such decrease, any decrease due to depletion resulting from production or due to
changes in oil and gas prices and any increase due to discoveries or additions)
that is less than 20% of the amount of the Partner's proved reserves set forth
in the Partner Reserve Report, shall not be considered in determining whether a
Partner Material Adverse Effect has occurred or is reasonably likely to occur,
provided, further, that any disagreement over the extent of any such reserve
decrease shall be resolved by prompt submittal to an independent reservoir
engineer reasonably acceptable to both parties whose decision shall be binding
and shall be delivered no later than five business days following submittal; (v)
any tax election or any settlement of any income tax liability or tax attributes
that individually or in the aggregate is reasonably likely to adversely affect
the tax liability or tax attributes of Partner or any of its Subsidiaries in any
material respect or any settlement or compromise of any material income tax
liability; (vi) any modification, assignment, termination or relinquishment of
rights under any Partner Material Contract by Partner or any of its Subsidiaries
other than such modification, assignment, termination or relinquishment in the
ordinary course of business consistent with past practice; or (vii) any damage,
destruction or casualty loss, whether or not covered by insurance, that
individually or in the aggregate would be reasonably likely to have a Partner
Material Adverse Effect (it being understood that the availability of any
insurance coverage shall be taken into
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account in determining whether such damage, destruction or loss would be
reasonably likely to have a Partner Material Adverse Effect).

SECTION 4.07  Taxes.

     (a) Except as would not be reasonably likely, individually or in the
aggregate, to have a Partner Material Adverse Effect, (i) Partner and each of
its Subsidiaries have, or prior to the Closing Date will have, (A) filed all
federal, state, local and foreign tax returns and reports required to be filed
by them prior to the date of this Agreement (taking into account extensions),
(B) paid or accrued all Taxes due and payable with respect to the periods
covered by such tax returns and reports or otherwise due and payable on or prior
to the Closing Date and (C) paid or accrued all Taxes for which a notice of
assessment or collection has been received (other than amounts being contested
in good faith by appropriate proceedings), (ii) neither the IRS nor any other
taxing authority has asserted or proposed in writing any claim or adjustment
relating to Taxes, or to the actual knowledge of the executive officers of
Partner, is threatening to assert any claims for Taxes, (iii) Partner and each
of its Subsidiaries have withheld or collected and paid over to the appropriate
governmental authorities (or are properly holding for such payment) all Taxes
required by law to be withheld or collected, and (iv) there are no liens for
Taxes upon the assets of Partner or any of its Subsidiaries (other than liens
for Taxes that are not yet due or that are being contested in good faith by
appropriate proceedings).

     (b) To Partner's knowledge, there exists no claim by a Tax authority in a
jurisdiction where any of Partner and its Subsidiaries does not file Tax returns
that it is or may be subject to taxation in that jurisdiction. There are no Tax
allocation or sharing agreements or arrangements affecting any of Partner and
its Subsidiaries. No payments are due or will become due by any of Partner and
its Subsidiaries pursuant to any such agreement or arrangement or any tax
indemnification agreement. Neither Partner nor any of its Subsidiaries will be
required to include any amount in income for any taxable period beginning after
December 31, 1999 as a result of a change in accounting or pursuant to any
agreement with any Tax authority with respect to any prior taxable period.
Neither Partner nor any of its Subsidiaries (i) has been a member of an
affiliated group filing a consolidated federal income Tax return (other than a
group the common parent of which was Partner) or (ii) has any liability for the
Taxes of any person or entity (other than any of Partner and its Subsidiaries)
under Treasury Regulation Section 1.1502-6 (or any similar provision of state,
local or foreign law), as a transferee or successor, by contract, or otherwise.
Neither Partner nor any of its Subsidiaries have entered into any agreement or
arrangement with any Tax authority that requires any of Partner and its
Subsidiaries to take any action or to refrain from taking any action.

SECTION 4.08  Properties.

     (a) Except for goods and other property sold, used or otherwise disposed of
since June 30, 2000 in the ordinary course of business, Partner and its
Subsidiaries have Good and Marketable Title (as defined below), for oil and gas
purposes, in and to all federal leases covering acreage offshore in the Gulf of
Mexico and to all the proved reserves reflected in the Partner Reserve Report
(as defined in Section 4.17) as owned by Partner and its Subsidiaries, and
defensible title for oil and gas purposes to all other properties, interests in
properties and assets, real and personal, reflected in the Partner Balance Sheet
as owned by Partner and its Subsidiaries, free and clear of any Liens, except:
(i) Liens associated with obligations reflected in the Partner Reserve Report or
the Partner Balance Sheet; (ii) Liens for current taxes not yet due and payable,
(iii) materialman's, mechanic's, repairman's, employee's, contractor's,
operator's, and other similar liens, charges or encumbrances arising in the
ordinary course of business (A) if they have not been perfected pursuant to law,
(B) if perfected, they have not yet become due and payable or payment is being
withheld as provided by law, or (C) if their validity is being contested in good
faith by appropriate action, (iv) all rights to consent by, required notices to,
filings with, or other actions by governmental entities in connection with the
sale or conveyance of oil and gas leases or interests if they are customarily
obtained subsequent to the sale or conveyance, and (v) such imperfections of
title, easements and Liens as would not reasonably be expected to have,
individually or in the aggregate, a Partner Material Adverse Effect. All leases
and other agreements pursuant to which Partner or any of its Subsidiaries leases
or otherwise acquires or obtains operating rights affecting any real or personal
property are in good standing, valid and effective and all royalties, rentals
and

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other payments due by the Partner to any lessor of any such oil and gas leases
have been paid, except in each case, as would not, individually or in the
aggregate, reasonably be expected to have a Partner Material Adverse Effect. All
major items of operating equipment of Partner and its Subsidiaries are in good
operating condition and in a state of reasonable maintenance and repair,
ordinary wear and tear excepted, except as would not, individually or in the
aggregate, reasonably be expected to have a Partner Material Adverse Effect.

     (b) The term "Good and Marketable Title" shall, for purposes of this
Section 4.08, with respect to Partner and its Subsidiaries, mean such title
that: (1) is deducible of record (from the records of the applicable parish or
county or (A) in the case of federal leases, from the records of the applicable
office of the Minerals Management Service or Bureau of Land Management, (B) in
the case of Indian leases, from the applicable office of the Bureau of Indian
Affairs, (C) in the case of state leases, from the records of the applicable
state land office) or is assignable to Partner or its Subsidiaries out of an
interest of record (as so defined) by reason of the performance by Partner or
its Subsidiaries of all operations required to earn an enforceable right to such
assignment; (2) is free from reasonable doubt to the end that a prudent
purchaser engaged in the business of the ownership, development and operation of
producing oil and gas properties with knowledge of all of the facts and their
legal bearing would be willing to accept and pay full value for the same and a
prudent lender would be willing to lend against it as collateral without
discount for title matters; (3) entitles Partner or its Subsidiaries to receive
not less than the interest set forth in the Partner Reserve Report with respect
to each proved property evaluated therein under the caption "Net Revenue
Interest" or "NRI" without reduction during the life of such property except as
stated in the Partner Reserve Report; (4) obligates Partner or its Subsidiaries
to pay costs and expenses relating to each such proved property in an amount not
greater than the interest set forth under the caption "Working Interest" or "WI"
in the Partner Reserve Report with respect to such property without increase
over the life of such property except as shown on the Partner Reserve Report;
and (5) does not restrict the ability of Partner or its Subsidiaries to utilize
the properties as currently intended.

SECTION 4.09  Intellectual Property.

     Each of Partner and its Subsidiaries owns, or is licensed or otherwise
possesses legally enforceable rights to use, all Intellectual Property that is
necessary to conduct the business of Partner and its Subsidiaries as currently
conducted, including without limitation, any seismic data or information used by
Partner and its Subsidiaries, subject to such exceptions that, individually or
in the aggregate, would not be reasonably likely to have a Partner Material
Adverse Effect. No person or entity has notified either Partner or any of its
Subsidiaries that their use of the Intellectual Property infringes on the rights
of any person or entity, subject to such claims and infringements as do not,
individually or in the aggregate, give rise to any liability on the part of
Partner and its Subsidiaries that would be reasonably likely to have a Partner
Material Adverse Effect, and to Partner's knowledge, no person is infringing on
any right of Partner or any of its Subsidiaries with respect to any such
Intellectual Property. No claims are pending or, to Partner's knowledge,
threatened that Partner or any of its Subsidiaries is infringing upon the rights
of any person or entity with regard to any Intellectual Property that,
individually or in the aggregate, would be reasonably likely to have a Partner
Material Adverse Effect.

SECTION 4.10  Contracts.

     (a) Set forth in Section 4.10 of the Partner Disclosure Schedule is a list
of each contract, lease, indenture, agreement, arrangement or understanding to
which Partner or any of its Subsidiaries is a party or subject that would be
required to be included as an exhibit to a Form S-1 Registration Statement
pursuant to the rules and regulations of the SEC if such a registration
statement were to be filed by the Partner on the date hereof and no previous
filings had been made (collectively, the "Partner Material Contracts").

     (b) Except for such matters that, individually or in the aggregate, would
not be reasonably expected to have a Partner Material Adverse Effect, with
respect to the Partner Material Contracts, (A) all Partner Material Contracts
are in full force and effect and are the valid and legally binding obligations
of Partner or the Subsidiary party thereto, and to Partner's knowledge, the
legally binding obligations of the other parties thereto, and are enforceable in
accordance with their respective terms, subject to the Bankruptcy and Equity
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<PAGE>   127

Exception; (B) Partner or the Subsidiary party thereto is not in breach or
default (nor does there exist any condition which upon the passage of time or
the giving of notice or both would reasonably be expected to cause such a breach
or default) with respect to, and to the knowledge of Partner, no other party to
any Partner Material Contract is in breach or default with respect to, its
obligations thereunder, including with respect to payments or otherwise; and (C)
no party to any Partner Material Contract has given written notice to Partner or
the Subsidiary party thereto of any action to terminate, cancel, rescind or
procure a judicial reformation thereof.

SECTION 4.11  Investigations; Litigation.

     Section 4.11 of the Partner Disclosure Schedule sets forth a list of all
pending Litigation Matters. Except as described in the Partner SEC Reports filed
prior to the date hereof or pursuant to the pre-merger notification process
under the HSR Act with respect to this transaction (i) no investigation or
review by any Governmental Entity with respect to Partner or any of its
Subsidiaries or any of the transactions contemplated by this Agreement is
pending, nor to Partner's knowledge has any Governmental Entity (foreign or
domestic) indicated an intention to conduct the same, (ii) there is no
Litigation Matter against Partner or any of its Subsidiaries pending or, to
Partner's knowledge, threatened, and (iii) there are no outstanding orders,
rulings, injunctions, awards, decrees, judgments or stipulations by or with any
court or administrative agency or by arbitration, that in the case of each of
(i), (ii) and (iii) above, individually or in the aggregate, if determined
adversely to Partner or any of its Subsidiaries, would have a Partner Material
Adverse Effect or would materially impair or delay the ability of Partner to
consummate the transactions contemplated by this Agreement.

SECTION 4.12  Environmental Matters.

     Except as disclosed in the Partner SEC Reports filed and publicly available
prior to the date hereof and, in case of clauses (i)-(iv) and (viii)-(ix) and
(xi), except for such matters that, individually or in the aggregate, are not
reasonably likely to have a Partner Material Adverse Effect: (i) Partner and its
Subsidiaries have complied with all applicable Environmental Laws and, to the
knowledge of Partner, there are no facts or circumstances that could reasonably
be expected to prevent or preclude future compliance with all applicable
Environmental Laws; (ii) the properties currently owned or operated by Partner
and its Subsidiaries (including soils, groundwater, surface water, buildings or
other structures) are not contaminated with any Hazardous Substances; (iii) to
the knowledge of Partner, the properties formerly owned or operated by Partner
or any of its Subsidiaries were not contaminated with Hazardous Substances
during the period of ownership or operation by Partner or any of its
Subsidiaries; (iv) Partner's and its Subsidiaries' properties have been used by
Partner and its Subsidiaries solely for oil and gas exploration, production,
processing, transportation and related operations and to its knowledge have not
been used, whether by Partner, its Subsidiaries or any other person or entity,
for the generation, storage or disposal of a Hazardous Substance (other than
those substances lawfully used and contained in oil and gas operations) or as a
landfill or other waste disposal site; (v) neither Partner nor any of its
Subsidiaries, within the five years immediately preceding the date hereof, has
received any written notice, demand, letter, claim or request for information
alleging that Partner or any of its Subsidiaries may be in violation of or
liable under any Environmental Law; (vi) neither Partner nor any of its
Subsidiaries is subject to any orders, decrees, injunctions or other
arrangements with any Governmental Entity or (except for indemnities under
purchase and sale agreements, operating agreements, farm-out agreements or other
similar agreements, whereby Partner or any of its Subsidiaries has acquired,
disposed of, or operated oil and gas properties, as to which (A) no existing
claim is pending or to its knowledge threatened against Partner or any of its
Subsidiaries and (B) Partner is not aware of any facts or circumstances that
could reasonably be expected to form the basis for a claim) is subject to any
indemnity or other agreement with any third party relating to liability under
any Environmental Law or relating to Hazardous Substances, including without
limitation any arrangements that require any change in the present condition or
operation of any of its properties in order to comply with conditions or
restrictions that relate to the protection of the environment; (vii) there are
no actions, suits, claims or proceedings seeking money damages, injunctive
relief, remedial action or other remedy pending or, to Partner's knowledge,
threatened against Partner or its Subsidiaries relating to the violation of, or
noncompliance with, an Environmental Law;
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<PAGE>   128

the disposal, discharge, or release of any Hazardous Substance; or the exposure
of any person to any other solid waste, pollutant, chemical substance, noise or
vibration; (viii) each of Partner and its Subsidiaries has obtained all permits,
licenses and other authorizations which are required under Environmental Laws
for the conduct of its existing drilling and development operations and is in
compliance with all terms and conditions of such permits, licenses and
authorizations; (ix) all necessary applications, inspection reports,
certificates and other instruments pertaining to Environmental Laws on
properties operated by Partner or any of its Subsidiaries have been filed with
the appropriate Governmental Entity; (x) neither the execution of this Agreement
nor the consummation of the transactions contemplated by this Agreement will
violate any Environmental Law or require the consent or approval of any agency
charged with enforcing any Environmental Law, which violation or the failure to
obtain such consent or approval would materially impair or delay the ability of
Partner to consummate the transactions contemplated by this Agreement; and (xi)
there are no circumstances or conditions involving Partner or any of its
Subsidiaries that could reasonably be expected to result in any claims,
liability, investigations, costs or restrictions on the ownership, use or
transfer of any property of Partner pursuant to any Environmental Law.

SECTION 4.13  Employee Benefit Plans.

     (a) Partner has listed in Section 4.13(a) of the Partner Disclosure
Schedule, and has provided to Company complete and correct copies of, all
employee benefit plans (as defined in Section 3(3) of ERISA and all bonus, stock
option, stock purchase, incentive, deferred compensation, supplemental
retirement, severance, and other similar employee benefit plans, written or
otherwise, for the benefit of, or relating to, any current or former employee or
other service provider of Partner, any Subsidiary of Partner or any trade or
business (whether or not incorporated) which is treated as a single employer
with Partner or any Subsidiary of Partner (a "Partner ERISA Affiliate") within
the meaning of Section 414(b), (c), (m) or (o) of the Internal Revenue Code
(together, the "Partner Employee Plans").

     (b) With respect to each Partner Employee Plan, Partner has made available
to Company, a true and correct copy of (i) the most recent annual report (Form
5500) filed with the IRS for each Partner Employee Plan with respect to which
such report is required to be filed, (ii) each trust agreement and group annuity
contract or insurance policy, if any, relating to such Partner Employee Plan,
(iii) the most current favorable determination letter received from the IRS as
to the qualified status under the Internal Revenue Code of each Partner Employee
Plan subject to Section 401 of the Internal Revenue Code, and (iv) the most
recent summary plan description for each Partner Employee Plan required to have
such a summary plan description. None of Partner, any Subsidiary of Partner or
any Partner ERISA Affiliate sponsors, maintains or contributes to, nor has any
such entity at any time within six years preceding the date of this Agreement
sponsored, maintained or contributed to, any plan that is subject to Title IV of
ERISA (including without limitation a multiemployer plan within the meaning of
Section 3(37) of ERISA), Section 302 of ERISA or Section 412 of the Internal
Revenue Code. Each Partner Employee Plan intended to be qualified under Section
401 of the Internal Revenue Code has been administered and maintained in all
material respects in accordance with its terms and all applicable laws,
including ERISA and the Internal Revenue Code, and each such plan has received a
favorable determination letter from the Internal Revenue Service regarding such
qualified status. There has been no termination or partial termination of any
such plan within the meaning of Section 411(d)(3) of the Internal Revenue Code.
There are no actions, suits or claims pending (other than routine claims for
benefits) or, to Partner's knowledge, threatened against, or with respect to,
any of the Partner Employee Plans or their assets. There is no matter pending
(other than routine qualification determination filings) with respect to any of
the Partner Employee Plans before any Governmental Entity.

     (c) With respect to the Partner Employee Plans, individually and in the
aggregate, no event has occurred, and to the knowledge of Partner, there exists
no condition or set of circumstances in connection with which Partner could be
subject to any material liability under ERISA, the Internal Revenue Code or any
other applicable law.

     (d) With respect to the Partner Employee Plans, individually and in the
aggregate, there are no funded benefit obligations for which contributions have
not been made or properly accrued and there are no unfunded benefit obligations
which have not been accounted for by reserves, or otherwise properly footnoted
in
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<PAGE>   129

accordance with generally accepted accounting principles, on the financial
statements of Partner, which obligations are reasonably likely to have a Partner
Material Adverse Effect.

     (e) Except as disclosed in the Partner SEC Reports filed prior to the date
of this Agreement, and except as provided for in this Agreement, neither Partner
nor any of its Subsidiaries is a party to any oral or written (i) agreement with
any officer or other key employee of Partner or any of its Subsidiaries, the
benefits of which are contingent, or the terms of which are materially altered,
upon the occurrence of a transaction involving Partner of the nature
contemplated by this Agreement, (ii) agreement with any officer of Partner
providing any term of employment or compensation guarantee, or (iii) agreement
or plan, including any stock option plan, stock appreciation right plan,
restricted stock plan or stock purchase plan, any of the benefits of which will
be increased, or the vesting of the benefits of which will be accelerated, by
the occurrence of any of the transactions contemplated by this Agreement or the
value of any of the benefits of which will be calculated on the basis of any of
the transactions contemplated by this Agreement.

SECTION 4.14  Compliance with Laws.

     Neither Partner nor any of its Subsidiaries is in violation or default of,
or has received any notices of violation or default with respect to, any
applicable federal, state, local or foreign statute, law, rule, order, decree or
regulation, including without limitation, any filing or reporting requirement
thereunder with respect to the conduct of its business, or the ownership or
operation of its business, except for violations or defaults that, individually
or in the aggregate, are not reasonably likely to have a Partner Material
Adverse Effect. Each of Partner and its Subsidiaries has all Permits legally
required to enable it to carry on its business as currently carried on and such
Permits are all in full force and effect and no proceeding is pending and
neither Partner nor any of its Subsidiaries has received any written notice of
any action seeking the revocation or limitation of or is in default or violation
of, any such Permit, except in each case as would not reasonably be expected to
have a Partner Material Adverse Effect; provided, however, that notwithstanding
the foregoing, no representation or warranty in this Section 4.14 is made with
respect to Permits issued pursuant to Environmental Laws, which are covered
exclusively by the provisions set forth in Section 4.12, or with respect to
Permits to conduct exploratory operations which have not been commenced as of
the date of this Agreement.

Section 4.15  Tax Matters.

     To its knowledge, after consulting with its Tax counsel, neither Partner
nor any of its Affiliates has taken or agreed to take any action that would
prevent the Merger from constituting a transaction qualifying as a
reorganization under Section 368(a) of the Internal Revenue Code.

Section 4.16  Opinion of Financial Advisor.

     The financial advisor of Partner, Merrill Lynch & Co., has delivered to
Partner an opinion dated the date of this Agreement to the effect that, based
upon and subject to the matters set forth therein, the Exchange Ratio is fair to
Partner from a financial point of view. Partner has delivered, or will deliver
promptly after receipt of such written opinion, a copy of such written opinion
to Company.

Section 4.17  Oil and Gas Reserves.

     Partner has furnished Company the Partner's estimates of Partner's and its
Subsidiaries' oil and gas reserves as of December 31, 1999 in a report as
described in Section 4.17 of the Partner Disclosure Schedule (the "Partner
Reserve Report"). Except as would not reasonably be expected to have a Partner
Material Adverse Effect, the factual, non-interpretive data on which the Partner
Reserve Report was based for purposes of estimating the oil and gas reserves set
forth in the Partner Reserve Report and in any supplement thereto or update
thereof furnished to Partner was accurate and incorporates the following: the
interests owned by Partner and its Subsidiaries at the time the Partner Reserve
Report was prepared, the cost of operating the properties, all production and
cost data adjusted for all oil and/or gas imbalances due, all tests and
operations on Partner's and its Subsidiaries' properties of which Partner was
aware at the time the Partner Reserve

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<PAGE>   130

Report was prepared and all capital costs reasonably expected by Partner at such
time to be necessary to operate, develop and plug and abandon the properties
described therein. To the best knowledge of Partner, and based on the
information given to Partner by third-party operators for all wells not operated
by Partner, the Partner Payout Balances (as defined below) for each of the wells
as used in the Partner Reserve Report were accurate as of the dates to which
Partner had calculated them, except as would not reasonably be expected to have
a Partner Material Adverse Effect. "Partner Payout Balances" means the status,
as of the dates of Partner's calculations, of the recovery by Partner or a third
party of a cost amount specified in the contract relating to a well out of the
revenue from such well where the net revenue interest of Partner therein will be
reduced or increased when such amount has been recovered. Partner agrees that
Company will have access to the Partner Reserve Report in accordance with the
procedures set forth in Section 4.17 of the Partner Disclosure Schedule.

SECTION 4.18  Take-or-Pay Deliveries.

     Except as provided in Partner SEC Reports or in Section 4.18 of the Partner
Disclosure Schedule, there are no calls (exclusive of market calls) on Partner's
oil or gas production and Partner has no obligation to deliver oil or gas
pursuant to any take-or-pay, prepayment or similar arrangement without receiving
full payment therefor.

SECTION 4.19  Hedging.

     Partner has set forth in Section 4.19 of the Partner Disclosure Schedule a
summary of Partner's position with respect to its Hedges as of the date hereof.
Except as set forth in Section 4.19 of the Partner Disclosure Schedule, neither
Partner nor any of its Subsidiaries is bound by any Hedges as of the date
hereof.

SECTION 4.20  Required Vote of Partner Stockholders.

     The affirmative vote of the holders of a majority of the outstanding shares
of Parent Common Stock is required to approve the amendment to Partner's
certificate of incorporation to increase its authorized capitalization. The
affirmative vote of a majority of the votes cast on the proposal, so long as the
total number of votes cast in favor of and against the proposal represents a
majority of the outstanding shares of Partner Common Stock, is required to
approve the issuance of Partner Common Stock pursuant to the Merger.

                                   ARTICLE V.

                              CONDUCT OF BUSINESS

SECTION 5.01  Covenants of Company.

     During the period from the date of this Agreement and continuing until the
earlier of the termination of this Agreement or the Effective Time, Company
agrees as to itself and each of its Subsidiaries (except to the extent that
Partner shall otherwise consent in writing), to carry on its operations in the
usual, regular and ordinary course of business in substantially the same manner
as previously conducted, to pay its debts and taxes when due subject to good
faith disputes over such debts or taxes, to pay or perform its other obligations
when due, and, to the extent consistent with such business, use all reasonable
efforts consistent with past practices and policies to preserve intact its
present business and its relationships with customers, suppliers and others with
whom Company deals in the ordinary course of its business. Company shall
promptly notify Partner of any material event or occurrence not in the ordinary
course of business of Company. Except as expressly contemplated by this
Agreement or as set forth in Section 5.01 of Company Disclosure Schedule,
subject to Section 6.01, Company shall not (and shall not permit any of its
Subsidiaries to), without the written consent of Partner:

          (a) Accelerate, amend or change the period of exercisability of
     options, restricted stock or other awards granted under any employee stock
     plan (including, without limitation, the Incentive Plan and the Performance
     Share Plan) of such party or authorize cash payments in exchange for any
     options granted

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<PAGE>   131

     under any of such plans except as required by the terms of such plans or
     any employment agreements or other related agreements in effect as of the
     date of this Agreement and set forth in Sections 3.13 and 3.16 of the
     Company Disclosure Schedule;

          (b) Declare or pay any dividends on or make any other distributions
     (whether in cash, stock or property) in respect of any of its capital
     stock, or split, combine or reclassify any of its capital stock or issue or
     authorize the issuance of any other securities in respect of, in lieu of or
     in substitution for shares of its capital stock, or purchase or otherwise
     acquire, directly or indirectly, any shares of its capital stock except
     from former employees, directors and consultants in accordance with
     agreements providing for the repurchase of shares in connection with any
     termination of service to such party;

          (c) Issue, deliver or sell, or authorize or propose the issuance,
     delivery or sale of, any shares of its capital stock or securities
     convertible into shares of its capital stock, or subscriptions, rights,
     warrants or options to acquire, or other agreements or commitments of any
     character obligating it to issue any such shares or other convertible
     securities, other than (i) the issuance of shares of Company Common Stock
     pursuant to the exercise of options outstanding on the date of this
     Agreement and referred to in Section 3.02 in accordance with their current
     terms or (ii) the issuance, earning or vesting of shares of Company Common
     Stock pursuant to outstanding performance share awards under the
     Performance Share Plan or other similar awards (including without
     limitation restricted stock awards under the Incentive Plan) made prior to
     the date of this Agreement in accordance with their current terms;

          (d) Acquire or agree to acquire by merging or consolidating with, or
     by purchasing a substantial equity interest in or substantial portion of
     the assets of, or by any other manner, any business or any corporation,
     partnership or other business organization or division, except as set forth
     in Section 5.01(k);

          (e) Except in accordance with the Retention Policy or pursuant to the
     current terms of Company's existing contracts, obligations or agreements
     set forth in Section 3.13 or Section 3.16 of the Company Disclosure
     Schedule or in connection with the payment of non-discretionary
     contributions to Company's 401(k) Plan at a level of 3% of eligible
     compensation and the payment of year-end bonuses (which year-end bonuses
     will not exceed $1.8 million in the aggregate for all employees, including
     officers, and are expected to be paid prior to the Effective Time or
     December 31, 2000, whichever occurs first), (i) increase or agree to
     increase the compensation payable or to become payable to its employees or
     officers, (ii) grant any additional severance or termination pay to, or
     enter into any employment or severance agreements with, any employees or
     officers, (iii) enter into any collective bargaining agreement (other than
     as required by law or extensions to existing agreements in the ordinary
     course of business), (iv) amend any Company Employee Plan (other than any
     amendment that does not increase Company's (or any successor's) obligations
     under such Company Employee Plan or that does not provide additional
     rights, including vesting rights, or benefits to any employee, except for
     accelerated vesting in connection with any termination of the Company's
     401(k) Plan as provided in Section 6.14(a)) or establish, adopt, enter into
     or amend any bonus, profit sharing, thrift, compensation, stock option,
     restricted stock, pension, retirement, deferred compensation, employment,
     termination, severance or other plan, trust, fund, policy or arrangement
     for the benefit of any directors, officers or employees, except to the
     extent required by applicable law, or (v) pay any material benefit or
     amount not required by a plan or arrangement as in effect on the date of
     this Agreement to any person;

          (f) Amend or propose to amend its Certificate of Incorporation or
     Bylaws, except as contemplated by this Agreement;

          (g) Incur, assume, guarantee or prepay any indebtedness for borrowed
     money, other than under Company's existing credit facility in the ordinary
     course of business; provided that in the case of any such incurrence,
     assumption, guarantee or prepayment that exceeds, individually or in the
     aggregate, $500,000, such incurrence, assumption, guarantee or prepayment
     is made after consultation with Partner;

          (h) Modify or terminate any of the Company Material Contracts or waive
     or relinquish any right thereunder, other than any amendment to Company's
     credit facility to reflect a redetermination of

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<PAGE>   132

     Company's borrowing base thereunder and other than any modification,
     termination, waiver or relinquishment that is not adverse to Company;

          (i) Enter into any Hedges or fixed price commodity sales agreements;

          (j) Make any material Tax election or settle or compromise any
     material Tax liability;

          (k) Except as permitted by Section 5.01(k) of the Company Disclosure
     Schedule, (i) make any material capital expenditure, except as may be
     required to (A) continue operations on the drilling, completion or plugging
     of any well or any well operation for which Company has consented to
     participate and is required to continue to participate pursuant to
     applicable agreements or (B) conduct emergency operations on any well,
     platform, pipeline or other production facility, (ii) enter into any sale,
     lease, farm-out or similar disposition (except for the sale of Hydrocarbons
     or personal property in the ordinary course of business) of any (A) proved
     reserves described on the Company Reserve Report or (B) interests in
     properties (other than proved reserves, which are addressed by the
     preceding clause) without first granting Partner the option (to be
     exercised within five days) to acquire such interests on the same terms as
     they are being offered to a third party or industry, provided that Company
     shall have the right to relinquish interests in such properties pursuant to
     elections not to participate in operations proposed by third parties under
     operating agreements or other applicable agreements so long as (to the
     extent allowed under such agreements) in each such case Company has
     promptly offered Partner the option to participate for, and thereby
     acquire, Company's interest in such operation and Partner has either
     affirmatively rejected such option or failed to respond in the manner
     provided for in such agreement within one-half of the response time
     required therein for Company to respond to the proposing party (provided
     that in the event of a required response time of less than 48 hours,
     Company shall use its reasonable best efforts to notify Partner at least 24
     hours prior to the anticipated receipt of such notice), (iii) enter into
     any material joint venture agreement, partnership agreement or similar
     agreement not in conjunction with acquisitions or capital expenditures
     contemplated in this Section 5.01(k) or Section 5.01(k)of the Company
     Disclosure Schedule or (iv) acquire or agree to acquire any assets (other
     than inventory, equipment and other similar items in the ordinary course of
     business); provided, however, neither Company nor any of its Subsidiaries
     shall be permitted to enter into any transaction with any third party in
     which, to Company's knowledge, any officer or director of Company has,
     directly or indirectly, any existing or prospective equity or other
     ownership interest or any other arrangement or understanding having the
     same economic effect, other than with respect to any company that is
     publicly traded on a national securities market or exchange, to the extent
     such ownership interest is less than two percent (2%) of such publicly
     traded company; and provided, further, however, that the Company shall not
     enter into any sale, lease, farmout, or other alienation or disposition of
     any interest in those 11 prospects specified in Section 5.01(k) of the
     Company Disclosure Schedule.

          (l) Change any method of accounting or accounting practice by Company
     or any of its Subsidiaries, except for any such change required by GAAP;

          (m) Adopt a plan of complete or partial liquidation, dissolution, or
     reorganization;

          (n) Waive, release, assign, or settle any material rights, claims or
     pending or threatened Litigation Matters;

          (o) Enter into any contract, agreement, arrangement or understanding
     that materially limits or otherwise materially restricts Company or any of
     its Subsidiaries or any successor thereto, or that would, after the
     Effective Time, limit or restrict the Surviving Corporation and its
     Affiliates (including Partner) or any successor thereto, from engaging in
     or competing in any line of business or in any geographic area (except for
     confidentiality agreements relating to specific prospects); or

          (p) Take, or agree in writing or otherwise to take, any of the actions
     described in Section 5.01(a) through Section 5.01(o) above.

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<PAGE>   133

SECTION 5.02  Covenants of Partner.

     During the period from the date of this Agreement and continuing until the
earlier of the termination of this Agreement or the Effective Time, Partner
agrees as to itself and its Subsidiaries (except to the extent that Company
shall otherwise consent in writing), to carry on its operations in the usual,
regular and ordinary course of business in substantially the same manner as
previously conducted, to pay its debts and taxes when due subject to good faith
disputes over such debts or taxes, to pay or perform its other obligations when
due, and, to the extent consistent with such business, use all reasonable
efforts consistent with past practices and policies to preserve intact its
present business. Partner shall promptly notify Company of any material event or
occurrence not in the ordinary course of business of Partner. Except as
expressly contemplated by this Agreement or as set forth in Section 5.02 of the
Partner Disclosure Schedule, subject to Section 6.01, Partner shall not (and
shall not permit any of its Subsidiaries to), without the written consent of
Company:

          (a) Declare or pay any dividends on or make any other distributions
     (whether in cash, stock or property) in respect of any of its capital
     stock, or split, combine or reclassify any of its capital stock or issue or
     authorize the issuance of any other securities in respect of, in lieu of or
     in substitution for shares of its capital stock; provided, however, that
     Partner shall be entitled to effect a stock split so long as an appropriate
     adjustment is made to the Exchange Ratio;

          (b) Issue shares of Partner Common Stock in connection with any
     acquisition of equity interests or assets that could reasonably be expected
     to adversely affect the ability of Partner to consummate or would
     reasonably be expected to otherwise delay the Merger;

          (c) Amend or propose to amend its Certificate of Incorporation or
     Bylaws, except as contemplated by this Agreement;

          (d) Adopt a plan of complete or partial liquidation, dissolution, or
     reorganization;

          (e) Change any method of accounting or accounting practice by Partner
     or any of its Subsidiaries, except for any such change required by GAAP; or

          (f) Take, or agree in writing or otherwise to take, any of the actions
     described in Section 5.02(a) through Section 5.02(e) above.

SECTION 5.03  Cooperation.

     Subject to compliance with applicable law, from the date hereof until the
Effective Time, each of Partner and Company shall confer on a regular and
frequent basis with one or more representatives of the other party to report on
the general status of ongoing operations and shall promptly provide the other
party or its counsel with copies of all filings made by such party with any
Governmental Entity in connection with this Agreement, the Merger and the
transactions contemplated hereby and thereby. Each party further agrees to work
in good faith and use its reasonable best efforts to satisfy all of the closing
conditions set forth in Article VII hereof, but is under no obligation to waive
any of such conditions.

                                  ARTICLE VI.

                             ADDITIONAL AGREEMENTS

SECTION 6.01  No Solicitation.

     Company shall not, and nor will it authorize or knowingly permit, directly
or indirectly, any officer, director, financial advisor, representative,
employee or agent of Company to, (i) solicit, initiate, or encourage any
proposals that constitute, or could reasonably be expected to lead to, a
proposal or offer for a merger, consolidation, business combination, share
exchange, recapitalization, sale of all or substantially all of its assets, sale
of shares (other than pursuant to the Incentive Plan or Performance Share Plan)
of capital stock (including without limitation by way of a tender offer) or
similar transaction involving Company or any of its Subsidiaries, other than the
transactions contemplated by this Agreement (any of the foregoing proposals

                                       30
<PAGE>   134

being referred to in this Agreement as an "Acquisition Proposal"), (ii) engage
in negotiations regarding, or provide any non-public information to any person
or entity relating to, or take any other action intended to facilitate, any
Acquisition Proposal, or (iii) agree to or recommend any Acquisition Proposal;
provided, however, that nothing contained in this Agreement shall prevent
Company, or its Board of Directors, prior to the date of the Company Stockholder
Meeting referred to in Section 6.05, from (A) furnishing non-public information
to, or entering into negotiations with, any person or entity in connection with
an unsolicited bona fide written Acquisition Proposal by such person or entity
or recommending an unsolicited bona fide written Acquisition Proposal to the
stockholders of Company, if and only to the extent that (1) such Acquisition
Proposal was not made by a person or entity with whom Company has actively
negotiated regarding an Acquisition Proposal within the three (3) month period
prior to the date of this Agreement, (2) Company's Board of Directors (after
consultation with its outside legal counsel) determines in good faith that such
action is legally advisable for the Board of Directors to comply with its
fiduciary duties to Company's stockholders under applicable law, (3) such
Acquisition Proposal is not subject to any financing contingencies or is, in the
good faith judgment of Company's Board of Directors (after consultation with its
financial advisor), reasonably capable of being financed by such other person or
entity, (4) Company's Board of Directors determines in good faith (after
consultation with its financial advisor) that such Acquisition Proposal is
reasonably capable, taking into account all legal, financial, regulatory and
other aspects of the proposal and the person or entity making the proposal, of
being completed and would, if consummated, result in a transaction more
favorable to Company's stockholders than the transaction contemplated by this
Agreement (any such more favorable Acquisition Proposal being referred to in
this Agreement as a "Superior Proposal"), and (5) prior to furnishing such
non-public information to, or entering into negotiations with, such person or
entity, Company's Board of Directors received from such person or entity an
executed confidentiality agreement with terms regarding confidentiality and
standstill provisions no less favorable to Company than those contained in the
existing Non-Disclosure Agreement between Partner and Company (the
"Confidentiality Agreement") and shall have notified Partner of any such
Acquisition Proposal, including the material terms and conditions thereof and
the identity of the person or entity making such proposal; or (B) complying with
Rule 14e-2 promulgated under the Exchange Act with regard to an Acquisition
Proposal.

SECTION 6.02  Joint Proxy Statement/Prospectus; Registration Statement.

     (a) As promptly as practicable after the execution of this Agreement,
Company and Partner shall prepare and file with the SEC the Joint Proxy
Statement (it being understood and agreed that both parties will use their
reasonable best efforts to accomplish this preparation and filing within three
(3) weeks after the date hereof), and Partner shall prepare and file with the
SEC the Registration Statement, in which the Joint Proxy Statement will be
included as a prospectus, provided that Partner may delay the filing of the
Registration Statement until approval of the Joint Proxy Statement by the SEC.
Partner and Company shall use their reasonable best efforts to respond to the
comments of the SEC in connection with the Joint Proxy Statement and the
Registration Statement, to furnish all information required to prepare the Joint
Proxy Statement and the Registration Statement and to cause the Registration
Statement to become effective as soon after such filing as practicable. Company
will use its reasonable best efforts to cause the Joint Proxy Statement to be
mailed to Company's stockholders, and Partner will use its reasonable best
efforts to cause the Joint Proxy Statement to be mailed to Partner's
stockholders, in each case as promptly as practicable after the Registration
Statement is declared effective under the Securities Act. The Joint Proxy
Statement shall include the recommendation of the Board of Directors of Company
in favor of this Agreement and the Merger and of the Board of Directors of
Partner (which original recommendation shall not be withdrawn or modified in a
manner adverse to Company) in favor of the issuance of Partner Shares pursuant
to the Merger and the amendment of Partner's certificate of incorporation to
increase its authorized capitalization; provided, however, that the Board of
Directors of Company may withdraw such recommendation under the circumstances
described in Section 6.01.

     (b) Partner and Company shall make all necessary filings with respect to
the Merger under the Securities Act, the Exchange Act, applicable state blue sky
laws and the rules and regulations thereunder.

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<PAGE>   135

     (c) Notwithstanding anything to the contrary in this Agreement, no party
hereto shall be prohibited from making factual disclosures to such party's
stockholders to the extent such party is required to do so by applicable law.

SECTION 6.03  Quotation on Stock Exchanges.

     Each of Company and Partner agrees to continue the quotation of Partner
Common Stock and Company Common Stock, respectively, on the New York Stock
Exchange and on the Nasdaq National Market System, during the term of this
Agreement.

SECTION 6.04  Access to Information.

     Upon reasonable notice, Company and Partner shall each (and shall use their
reasonable best efforts to cause each of their respective Subsidiaries,
officers, employees, accountants, counsel, engineers, consultants and other
representative (including but not limited to external accountants, engineers and
consultants)) to afford to the officers, employees, accountants, counsel,
engineers, consultants and other representatives (including but not limited to
external accountants, engineers and consultants) of the other (at the risk and
expense of such inspecting party), subject to each such inspecting party's
agreement (which need not be in writing) to be bound by the terms of the
Confidentiality Agreement or other customary form of acknowledgement of the
confidential nature of the information, reasonable access for purposes
reasonably related to this Agreement and the consummation of the transactions
contemplated hereby, during normal business hours during the period prior to the
Effective Time, to all its properties, books, contracts, commitments and records
and, during such period, each of Company and Partner shall (and shall cause each
of their respective Subsidiaries to) furnish promptly to the other (a) a copy of
each report, schedule, registration statement and other document filed or
received by it during such period pursuant to the requirements of federal
securities laws and (b) all other information concerning its business,
properties and personnel as such other party may reasonably request for purposes
reasonably related to this Agreement and the consummation of the transactions
contemplated hereby. Unless otherwise required by law, the parties will hold any
such information which is nonpublic in confidence in accordance with the
Confidentiality Agreement. No information or knowledge obtained in any
investigation pursuant to this Section 6.04 shall affect or be deemed to modify
any representation or warranty contained in this Agreement or the conditions to
the obligations of the parties to consummate the Merger.

SECTION 6.05  Stockholders Meetings.

     (a) Company and Partner each shall call a meeting of its respective
stockholders to be held as promptly as practicable for the purpose of voting, in
the case of Company, upon this Agreement and the Merger and, in the case of
Partner, upon the issuance of shares of Partner Common Stock pursuant to the
Merger and an amendment to Partner's certificate of incorporation to increase
its authorized capitalization (the "Partner Voting Proposal"). In accordance
with Section 251(c) of the DGCL, Company's obligation to call and hold its
stockholders meeting shall not be dependent on Company Board of Directors'
recommendation. Company and Partner shall coordinate and cooperate with respect
to the timing of such meetings and shall use their reasonable best efforts to
hold such meetings on the same day and as soon as practicable after the date
hereof. Except as otherwise permitted with respect to Company pursuant to
Section 6.01 of this Agreement, each party shall use its reasonable best efforts
to solicit from its stockholders proxies in favor of the matters set forth above
and obtain a sufficient vote in favor of such matters at its stockholders
meeting (or any postponement or adjournment thereof). Partner shall take such
action with respect to Merger Sub, and cause Merger Sub to take such action, as
may be required to consummate the Merger, including without limitation, voting
all shares of Merger Sub in favor of the Merger.

     (b) Each of Partner and Company shall use its reasonable best efforts to
cause each of its directors to enter into the Partner Voting Agreement or the
Company Voting Agreement, as the case may be, with respect to the shares owned
by such director, as soon as practicable after the date hereof.

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<PAGE>   136

SECTION 6.06  Legal Conditions to Merger.

     (a) Each of Company and Partner shall use its reasonable best efforts to
(i) take, or cause to be taken, all appropriate action, and do, or cause to be
done, all things necessary and proper under applicable law to consummate and
make effective the transactions contemplated hereby as promptly as practicable,
(ii) obtain from any Governmental Entity or any other third party any consents,
licenses, permits, waivers, approvals, authorizations, or orders required to be
obtained or made by it or any of its Subsidiaries in connection with the
authorization, execution and delivery by it of this Agreement and the
consummation by it of the transactions contemplated hereby including, without
limitation, the Merger, and (iii) as promptly as practicable, make all necessary
filings, and thereafter make any other required submissions, with respect to
this Agreement and the Merger required under (A) the Securities Act and the
Exchange Act, and any other applicable federal or state securities laws, (B)
subject to Section 6.06(b), the HSR Act and any related governmental request
thereunder and (C) any other applicable law. Company and Partner shall cooperate
with each other in connection with the making of all such filings, including
providing copies of all such documents to the non-filing party and its advisors
prior to filing and, if requested, to accept all reasonable additions, deletions
or changes suggested in connection therewith. Company and Partner shall use
their reasonable best efforts to furnish to each other all information required
for any application or other filing to be made pursuant to the rules and
regulations of any applicable law (including all information required to be
included in the Joint Proxy Statement and the Registration Statement) in
connection with the transactions contemplated by this Agreement.

     (b) Partner and Company agree, and shall cause each of their respective
Subsidiaries, to cooperate and to use their respective reasonable best efforts
to obtain any government clearances required for Closing (including through
compliance with the HSR Act and any applicable foreign government reporting
requirements), to respond to any government requests for information, and to
contest and resist any action, including any legislative, administrative or
judicial action, and to have vacated, lifted, reversed or overturned any decree,
judgment, injunction or other order (whether temporary, preliminary or
permanent) that restricts, prevents or prohibits the consummation of the Merger
or the transaction contemplated by this Agreement. Partner shall use its
reasonable best efforts to resolve such issues or objections, if any, as may be
asserted with respect to the consummation of the Merger or any other
transactions contemplated by this Agreement, including without limitation as may
arise under any antitrust, competition or trade regulatory laws, rules or
regulations of any domestic or foreign government or any governmental, judicial
or multinational authority. Notwithstanding the foregoing, nothing in this
Section 6.06 shall require, or be construed to require, Partner or Company, in
connection with the receipt of any regulatory approval, to proffer to or agree
to (A) sell or hold separate and agree to sell, divest or to discontinue or
limit, before or after the Effective Time, any assets, businesses, or interest
in any assets or businesses of Partner, Company or any of their respective
Affiliates (or to consent to any sale, or agreement to sell, or discontinuance
or limitation by Partner or Company, as the case may be, of any of its assets or
businesses), or (B) any conditions relating to, or changes or restrictions in,
the operations of any such assets or businesses which, in either case, could
reasonably be expected to result in a Partner Material Adverse Effect or a
Company Material Adverse Effect or to materially and adversely impact the
economic or business benefits to such party of the transactions contemplated by
this Agreement. The parties hereto will consult and cooperate with one another,
and consider in good faith the views of one another, in connection with any
analyses, appearances, presentations, memoranda, briefs, arguments, opinions and
proposals made or submitted by or on behalf of any party hereto in connection
with proceedings under or relating to the HSR Act or any other federal, state or
foreign antitrust or fair trade law.

     (c) Each of Company and Partner shall give (or shall cause its Subsidiaries
to give) any notices to third parties required to be given by it, and use, and
cause its Subsidiaries to use, its reasonable best efforts to obtain any third
party consents related to or required in connection with the Merger required to
be obtained by it that are (i) necessary for it to consummate the transactions
contemplated hereby, (ii) disclosed or required to be disclosed in the Company
Disclosure Schedule or Section 3.03(c) of this Agreement or the Partner
Disclosure Schedule, as the case may be or (iii) required to prevent a Company
Material Adverse Effect or a Partner Material Adverse Effect from occurring
prior to or after the Effective Time.

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<PAGE>   137

SECTION 6.07  Public Disclosure.

     Partner and Company shall consult with each other before issuing any press
release or otherwise making any public statement with respect to the Merger or
this Agreement and shall not issue any such press release or make any such
public statement prior to such consultation and the express prior written
approval of the other party, except as may be required by law and any applicable
stock exchange rules. With respect to any other press release to be issued by
Partner or Company prior to the Effective Time or termination of this Agreement,
the party issuing the press release shall endeavor to provide the other party
with a copy of any such press release by the close of business on the business
day prior to the issuance of such press release or, if such notice is
impracticable to provide, as soon as practicable prior to such release.

SECTION 6.08  Tax-Free Reorganization.

     Partner and Company shall each use their reasonable best efforts to cause
the Merger to be treated as a reorganization within the meaning of Section
368(a) of the Internal Revenue Code, and shall not knowingly take any actions
which could prevent the Merger from being treated as described in this Section
6.08.

SECTION 6.09  Affiliate Agreements.

     Upon the execution of this Agreement, Company will provide Partner with a
list of those persons who are, in Company's reasonable judgment, "affiliates" of
Company within the meaning of Rule 145 (each person who is an "affiliate" within
the meaning of Rule 145 is referred to as an "Affiliate") promulgated under the
Securities Act ("Rule 145"). Company shall use its reasonable best efforts to
deliver or cause to be delivered to Partner within 30 days after the date hereof
(and in any case prior to the Effective Time) from each of its Affiliates, an
executed Affiliate Agreement, in form and substance reasonably satisfactory to
Partner and Company, by which each Affiliate of Company agrees to comply with
the applicable requirements of Rule 145 and such requirements as may be
necessary for the Merger to be treated as a pooling of interests for accounting
purposes (an "Affiliate Agreement"). Partner shall be entitled to place
appropriate legends on the certificates evidencing any Partner Common Stock to
be received by such Affiliates of Company pursuant to the terms of this
Agreement, and to issue appropriate stop transfer instructions to the transfer
agent for the Partner Common Stock, consistent with the terms of the Affiliate
Agreements (provided that such legends or stop transfer instructions shall be
removed, two years after the Effective Date, upon the request of any stockholder
that is not then an Affiliate of Partner and that otherwise satisfies the resale
provisions of Rule 145(d)). Partner expressly agrees to cause the results of its
earnings for a period following consummation of the Merger that includes at
least 30 days of combined operations of Partner and Company to be publicly
released as soon as reasonably practicable (it being understood that Partner may
satisfy this obligation by filing its regularly prepared quarterly results on
Form 10-Q).

SECTION 6.10  New York Stock Exchange Quotation.

     Partner shall use its reasonable best efforts to cause the shares of
Partner Common Stock to be issued in the Merger to be approved for listing on
the New York Stock Exchange, subject to official notice of issuance, prior to
the Closing Date.

SECTION 6.11  Stock Plans.

     (a) At the Effective Time, each then outstanding option to purchase shares
of Company Common Stock (a "Company Stock Option") under the Incentive Plan,
whether vested or unvested (after giving effect to any applicable change in
control or similar type provisions), shall, together with the Incentive Plan, be
assumed by Partner and shall thereby be converted into an option to acquire, on
the same terms and conditions in effect for such Company Stock Option
immediately prior to the Closing Date, that number of shares of Partner Common
Stock determined by multiplying the number of shares of Company Common Stock
subject to that option immediately prior to the Closing Date by the Exchange
Ratio and rounding out to the next whole number of shares. The exercise price
per share of Partner Common Stock subject to each such assumed Company Stock
Option shall be equal to the amount determined by dividing the exercise price
per share of

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<PAGE>   138

Company Common Stock in effect for that Company Stock Option immediately prior
to the Closing Date by the Exchange Ratio and rounding up to the nearest whole
cent. Subject to the effect of Section 422(d) of the Internal Revenue Code on
any Company Stock Option with respect to which vesting is accelerated in
connection with the transactions contemplated by this Agreement, it is the
intention of the parties that each Company Stock Option so assumed by Partner
shall continue to qualify, after the Closing Date, as an incentive stock option
under Section 422 of the Internal Revenue Code to the same extent that option
qualified as such an incentive stock option immediately prior to the Closing
Date.

     (b) As soon as practicable after the Effective Time, Partner shall deliver
to the participants in the Incentive Plan, in form and substance reasonably
satisfactory to Company, an appropriate document evidencing the assumption of
each Company Stock Option in accordance with Section 6.11(a) of this Agreement.

     (c) Partner shall take all corporate action necessary to reserve for
issuance a sufficient number of shares of Partner Common Stock for delivery upon
the exercise of the Company Stock Options assumed in accordance with this
Section 6.11. As soon as practicable and in no event more than thirty (30) days
after the Effective Time, Partner shall file a registration statement on Form
S-8 (or any successor or other appropriate forms) with respect to the shares of
Partner Common Stock subject to such options or on another appropriate form of
registration statement for any such shares of Partner Common Stock which are not
registrable on Form S-8 and shall use its commercially reasonable best efforts
to maintain the effectiveness of such registration statement or registration
statements (and maintain the current status of the prospectus or prospectuses
contained therein) for so long as such options remain outstanding.

     (d) The Board of Directors of Company (or duly appointed committee thereof
that is authorized to administer the Incentive Plan) shall, prior to or as of
the Effective Time, take all necessary actions, pursuant to and in accordance
with the terms of the Incentive Plan and the instruments evidencing the Company
Stock Options, to provide for the conversion of the Company Stock Options into
options to acquire Partner Common Stock in accordance with this Section 6.11.

     (e) The shares of Company Common Stock currently subject to earn-out
schedules pursuant to the outstanding performance share awards under the
Performance Share Plan shall be earned or forfeited by the holders thereof at
the Effective Time in accordance with the change in control provisions of such
holders' share awards; provided, however, that any shares not earned based on
the most recently issued year-end financial statement prior to the Effective
Time shall be earned as determined prior to the Effective Time in good faith by
the Compensation and Incentive Committee under the Performance Share Plan (and
subject to the prior approval of Partner) based on the financial performance of
Company during the period beginning on the first day of the fiscal year in which
the Effective Time occurs and ending on the Closing Date. The earned shares
shall, at the Effective Time, be converted into shares of Partner Common Stock
in accordance with the Exchange Ratio.

     (f) The Board of Directors of Company shall, prior to or as of the
Effective Time, take appropriate action to approve the deemed cancellation of
the Company Stock Options for purposes of Section 16(b) of the Exchange Act. The
Board of Directors of Partner shall, prior to or as of the Effective Time, take
appropriate action to approve the deemed grant of options to purchase Partner
Common Stock under the Company Stock Options (as converted pursuant to this
Section 6.11) for purposes of Section 16(b) of the Exchange Act. The disposition
of such shares of Company Common Stock and the issuance of such shares of Parent
Common Stock in the Merger shall also be included in the approval process of the
Boards of Directors of Company and Parent for purposes of Section 16(b) of the
Exchange Act. Similar action shall be taken by Company and Partner Boards of
Directors with respect to the shares of Company Common Stock outstanding under
the Performance Share Plan which are to be converted into shares of Partner
Common Stock in the Merger.

     (g) If any shares of Company Common Stock are, immediately prior to the
Effective Time, unvested or subject to any other restrictions under the
Incentive Plan or any restricted stock purchase or stock issuance agreement to
which Company is a party and the vesting schedule or restrictions applicable to
those shares are not to vest or lapse on an accelerated basis in connection with
the Merger, then the shares of Partner Common Stock issued in exchange for such
shares of Company Common Stock in the Merger shall also be unvested
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<PAGE>   139

and subject to the same vesting schedule in effect for the unvested shares of
Company Common Stock immediately prior to the Effective Time. The certificates
representing such shares of Partner Common Stock may accordingly bear the
appropriate restrictive legends.

SECTION 6.12  Brokers or Finders.

     Each of Partner and Company represents, as to itself, its Subsidiaries and
its Affiliates, that no agent, broker, investment banker, financial advisor or
other firm or person is or will be entitled to any broker's or finder's fee or
any other commission or similar fee in connection with any of the transactions
contemplated by this Agreement except Goldman, Sachs & Co., whose fees and
expenses will be paid by Company in accordance with Company's agreement with
such firm (copies of which have been delivered by Company to Partner prior to
the date of this Agreement), and Merrill Lynch & Co., whose fees and expenses
will be paid by Partner in accordance with Partner's agreement with such firm (a
copy of which has been delivered by Partner to Company prior to the date of this
Agreement). Each of Partner and Company agrees to indemnify and hold the other
harmless from and against any and all claims, liabilities or obligations with
respect to any such fees, commissions or expenses asserted by any person on the
basis of any act or statement alleged to have been made by such party or any of
its Affiliates.

SECTION 6.13  Indemnification.

     (a) From and after the Effective Time, Partner agrees that it will, and
will cause the Surviving Corporation to, indemnify and hold harmless each
present and former director and officer of Company (the "Indemnified Parties"),
against any costs or expenses (including attorneys' fees), judgments, fines,
losses, claims, damages, liabilities or amounts paid in settlement
(collectively, "Costs") incurred in connection with any claim, action, suit,
proceeding or investigation, whether civil, criminal, administrative or
investigative, arising out of or pertaining to matters existing or occurring at
or prior to the Effective Time, whether asserted or claimed prior to, at or
after the Effective Time, to the fullest extent that Company would have been
permitted under the DGCL and its Certificate of Incorporation or Bylaws in
effect on the date hereof to indemnify such Indemnified Party (and Partner and
the Surviving Corporation shall also advance any expenses as incurred to the
fullest extent permitted under applicable law; provided the Indemnified Party to
whom expenses are advanced provides an undertaking to repay such advances if it
is ultimately determined that such Indemnified Party is not entitled to
indemnification).

     (b) For a period of six (6) years after the Effective Time, Partner shall
cause the Surviving Corporation to maintain (to the extent available in the
market) in effect a directors' and officers' liability insurance policy covering
those persons who are covered as of the date hereof by Company's directors' and
officers' liability insurance policy (a copy of which has been heretofore
delivered to Partner) with coverage in amount and scope at least as favorable as
Company's existing coverage; provided, that in no event shall Partner or the
Surviving Corporation be required to expend in excess of 200% of the annual
premium currently paid by Company for such coverage (currently approximately
$172,500) (the "Current Premium"); and if such premium would at any time exceed
200% of the Current Premium, then the Surviving Corporation shall maintain or
obtain as much of such insurance as can be so maintained or obtained at an
annual premium equal to 200% of the Current Premium.

     (c) The provisions of this Section 6.13 are intended to be an addition to
the rights otherwise available to the current officers and directors of Company
by law, charter, statute, bylaw or agreement, and shall operate for the benefit
of, and shall be enforceable by, each of the Indemnified Parties, their heirs
and their representatives.

SECTION 6.14  Benefit Matters.

     (a) If Partner requests in writing, Company shall take all action necessary
to terminate, or cause to terminate, before the Effective Time, any employee
benefit plan that is a 401(k) plan. Partner shall provide the opportunity for
participants in Company's 401(k) Plan who are employed by Partner or Company on
the date that is 60 days after the Closing Date to "roll over" their account
balances into Partner's 401(k) plan.

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<PAGE>   140

     (b) At the Effective Time or following a reasonable transition period as
set forth below, continuing employees of Company ("Continuing Employees") shall
be eligible to participate in those Partner Employee Plans maintained for
similarly situated employees of Partner (or in substantially similar programs),
on the same terms applicable to similarly situated employees of Partner and to
the extent that such plans and programs provide the following benefits:
medical/dental/vision care, life insurance, disability income, sick pay, holiday
and vacation pay, 401(k) plan coverage, Internal Revenue Code Section 125
benefit arrangements, bonus, profit-sharing or other incentive plans, pension or
retirement programs, dependent care assistance, severance benefits, and employee
stock option and stock purchase plans. Each Continuing Employee shall be given
credit for any vacation and sick leave time accrued, but unused, as of the day
immediately preceding the Effective Time (or, if later, the time of the
transition of such employee from a Company Employee Plan to a Partner Employee
Plan). Notwithstanding the foregoing, in lieu of causing the Continuing
Employees to participate in Partner Employee Plans as of the Effective Time,
Partner may, in its sole discretion, as to any one or more of such benefits,
cause the Continuing Employees to continue to participate in a Company Employee
Plan providing the relevant benefit described in the first sentence of this
paragraph for a reasonable transition period after the Effective Time. Each
Continuing Employee shall be given credit, for purposes of any service
requirements for participation or vesting (but not benefit accrual for purposes
of any defined benefit pension plan), for his or her period of service with
Company credited under a similar plan prior to the Closing Date, subject to
appropriate break in service rules. Each such employee shall, with respect to
any Partner plans or programs which have co-payment, deductible or other
co-insurance features, receive credit for any amounts such individual has paid
to date in the plan year of the Effective Time (or, if later, the time of the
transition of such employee from a Company Employee Plan to a Partner Employee
Plan) under comparable plans or programs maintained by Company prior to the
Effective Time. Each Continuing Employee and eligible dependent who, at the
Effective Time (or, if later, the time of the transition of such employee from a
Company Employee Plan to a Partner Employee Plan), was participating in an
employee group health plan maintained by Company shall not be excluded from
Partner's employee group health plan or limited in coverage thereunder by reason
of any waiting period restriction or pre-existing condition limitation to the
extent such restriction or limitation did not apply to such Continuing Employee
as of the Effective Time (of, if later, the time of transition of such employee
from a Company Employee Plan to a Partner Employee Plan) under Company's group
health plan.

     (c) Partner shall (or shall cause the Surviving Corporation to) make all
payments to be paid after the Effective Time pursuant to the provisions
contained in the Retention Policy applicable to all eligible employees of
Company. Without limiting Section 6.11, Partner shall recognize all vesting,
acceleration and other provisions under all written agreements containing change
in control type provisions applicable to Company's officers, employees or
directors in existence today and that have been made available to Partner and
that are listed on Section 6.14(c) of the Company Disclosure Schedule, and
Partner shall promptly make or cause to be made all payments to such individuals
required thereunder.

     (d) Notwithstanding any provision in this Agreement to the contrary, but
only to the extent permissible under Section 6.16, Company may facilitate the
elimination of loss of deductions and excise taxes under Sections 280G and 4999
of the Internal Revenue Code with respect to severance payments and other
benefits to be provided to the persons who are party to the agreements described
in Section 3.13(e) of the Company Disclosure Schedule by advancing to such
persons, upon request, an amount equal to the amount such persons are required
to pay to Company to satisfy Company's withholding tax obligation arising from
such persons' exercise of non-statutory stock options during 2000 in order to
increase the amount of their respective "Total 280G Base" calculations shown in
Section 3.13(f) of the Company Disclosure Schedule. Any amount so advanced shall
be evidenced by a full recourse promissory note in a form reasonably
satisfactory to Company and Partner, shall bear interest at the rate of 8% per
annum and shall be payable in full no later than five days following the Closing
Date. The amount of any such advance, together with accrued interest, may be
setoff against, and deducted from, the amount of any payments made to the
persons receiving such advance pursuant to the agreements identified in Section
3.13(e) of the Company Disclosure Schedule. No advance to any person pursuant to
this Section 6.14(d) shall exceed the amount payable to such person pursuant to
the applicable agreements identified in Section 3.13(e) of the Company
Disclosure Schedule.

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<PAGE>   141

     (e) Notwithstanding any provision in this Agreement to the contrary,
Company shall cause (i) the aggregate amount of annual bonuses that are paid or
payable to all employees of Company and its Subsidiaries for calendar year 2000
to not exceed $1.8 million and to be allocated among employees in a proportion
that is not materially different from prior practice, (ii) the aggregate amount
of retention and severance benefits to be paid or payable to all employees of
Company and its Subsidiaries under the Retention Policy to not exceed $2.6
million and $1.1 million, respectively, assuming all employees qualify for such
payments, and (iii) the aggregate amount of cash severance payments to be paid
or payable to all employees of Company and its Subsidiaries (exclusive of any
severance payments attributable to the accelerated vesting of options or
restricted stock or performance share awards) pursuant to the agreements
described on Section 3.13(e) of the Company Disclosure Schedule to not exceed
$7.0 million. Company represents and warrants to Partner that, except for the
amounts contemplated in (i) through (iii) of the preceding sentence, there are
no cash amounts which will be payable by Company or any of its Subsidiaries in
connection with the termination of any employment or consulting agreement to
which Company or any of its Subsidiaries is a party or in connection with the
termination of the employment or consulting relationship under any such
agreement.

     (f) Notwithstanding anything to the contrary contained in Sections 3.06,
3.08, and 5.01, until the Closing, Company may approve and assign overriding
royalty interests to its geoscientists pursuant to Company's existing Onshore
Geoscientist Overriding Royalty Interest Plan ("Onshore ORI Plan") and Gulf
Coast Geoscientist Overriding Royalty Interest Plan ("Offshore ORI Plan"). As
more particularly described in Section 5.01(k) of the Company Disclosure
Schedule, Company may expose up to $10 million in potential high bids at the
Central Gulf of Mexico Sale #178 ("Sale #178"), which is currently scheduled to
be held in March 2001. The Offshore ORI Plan shall apply to all leases acquired
by Company or Surviving Corporation, as the case may be, at Sale #178 regardless
of whether the sale is held prior to or after the Effective Time, provided that
notwithstanding anything to the contrary contained in this Agreement or in the
Offshore ORI Plan, Surviving Corporation shall not bear an overriding royalty
interest created by virtue of the Offshore ORI Plan that is greater than 2.5%,
proportionately reduced to Surviving Corporation's working interest in the
leases acquired pursuant to Sale #178. Company or Surviving Corporation, as the
case may be, shall convey the appropriate overriding royalty interests to those
geoscientists who qualify for such awards under the Offshore ORI Plan by virtue
of their continuing employment with Company or Surviving Corporation, as the
case may be, at the time of Sale #178 and who otherwise qualify for such awards
under the terms of the Offshore ORI Plan, it being understood that should any of
those geoscientists not be employed by Company or Surviving Corporation,
whichever is appropriate, as of the date of Sale #178, those that are not so
employed shall not be entitled to receive an overriding royalty interest in the
leases acquired pursuant to Sale #178. It is further agreed that until Sale #178
is concluded, only Company's Vice President of Gulf Coast Exploration shall have
the right to terminate the employment of any of Company's Gulf Coast
geoscientists for performance-based reasons, provided that he has received the
prior concurrence of the CEO of Partner. If the Closing occurs prior to Sale
#178, Surviving Corporation shall prepare and submit bids at Sale #178 in
accordance with Company's past practices, up to a total exposure of $10 million,
under the continuing supervision of Company's Vice President of Gulf Coast
Exploration and Vice President of Gulf Coast Operations, in consultation with
the CEO of Partner. Company shall offer to both of its Gulf Coast Vice
Presidents prior to the Effective Time an amendment to their respective
employment agreements or change-of-control employment agreements that extends
until the later of the time currently provided in such agreement or seven days
after the conclusion of Sale #178 the period in which such officer may elect to
terminate his employment and continue to qualify to receive compensation to
which he is entitled by reason of the occurrence of a Change of Control of
Company as defined in his respective agreement.

SECTION 6.15  Registration Statement; Joint Proxy Statement/Prospectus.

     The information to be supplied by Company for inclusion in the registration
statement on Form S-4 pursuant to which shares of Partner Common Stock issued in
the Merger will be registered under the Securities Act (the "Registration
Statement"), shall not at the time the Registration Statement is declared
effective by the SEC contain any untrue statement of a material fact or omit to
state any material fact required to be stated in the Registration Statement or
necessary in order to make the statements in the Registration Statement not
misleading. The information supplied by Company for inclusion in the joint proxy
statement/
                                       38
<PAGE>   142

prospectus (the "Joint Proxy Statement") to be sent to the stockholders of
Partner and Company in connection with the meeting of Company's stockholders to
consider this Agreement and the Merger (the "Company Stockholders' Meeting") and
the meeting of Partner's stockholders to consider the Partner Voting Proposal
(the "Partner Stockholders' Meeting") shall not, on the date the Joint Proxy
Statement is first mailed to stockholders of Company or Partner, at the time of
the Company Stockholders' Meeting and the Partner Stockholders' Meeting, contain
any statement which, in light of the circumstances under which it shall be made,
is false or misleading with respect to any material fact, or omit to state any
material fact necessary in order to make the statements made in the Joint Proxy
Statement not false or misleading; or omit to state any material fact necessary
to correct any statement in any earlier communication with respect to the
solicitation of proxies for the Company Stockholders' Meeting or the Partner
Stockholders' Meeting which has become false or misleading. If at any time prior
to the Effective Time any event relating to Company or any of its Affiliates,
officers or directors should be discovered by Company which should be set forth
in an amendment to the Registration Statement or a supplement to the Joint Proxy
Statement, Company shall promptly inform Partner. If at any time prior to the
Effective Time any event relating to Partner or any of its Affiliates, officers
or directors should be discovered by Partner which should be set forth in an
amendment to the Registration Statement or a supplement to the Joint Proxy
Statement, Partner shall promptly inform Company.

SECTION 6.16  Pooling Accounting.

     From and after the date hereof and until the Effective Time, neither
Company nor Partner, nor any of their respective Subsidiaries, shall knowingly
take any action, or knowingly fail to take any action, that would jeopardize the
treatment of the Merger as a pooling of interests for accounting purposes.

                                  ARTICLE VII.

                              CONDITIONS TO MERGER

SECTION 7.01  Conditions to Each Party's Obligation to Effect the Merger.

     The respective obligations of each party to this Agreement to effect the
Merger shall be subject to the satisfaction prior to, or, with respect to
Section 7.01(e), at, the Closing Date of the following conditions:

          (a) Stockholder Approval. This Agreement and the Merger shall have
     been approved and adopted by the requisite vote of the stockholders of
     Company as required by the DGCL and the Partner Voting Proposal shall have
     been approved by the requisite vote of the stockholders of Partner as
     required by the DGCL and the New York Stock Exchange.

          (b) HSR Act. The waiting period applicable to the consummation of the
     Merger under the HSR Act shall have expired or been terminated.

          (c) Approvals. Other than the Certificate of Merger which shall be
     filed in accordance with Section 1.01, all authorizations, consents, orders
     or approvals of, or declarations or filings with, or expirations of waiting
     periods imposed by, any Governmental Entity the failure of which to file,
     obtain or occur would have a Partner Material Adverse Effect or a Company
     Material Adverse Effect shall have been filed, been obtained or occurred.

          (d) Registration Statement. The Registration Statement shall have been
     declared effective under the Securities Act and shall not be the subject of
     any stop order or proceedings seeking a stop order.

          (e) No Injunctions. No Governmental Entity or federal, state or
     foreign court of competent jurisdiction shall have enacted, issued,
     promulgated, enforced or entered any Order, or statute, rule, regulation
     which is in effect and which has the effect of making the Merger illegal or
     otherwise prohibiting consummation of the Merger.

          (f) New York Stock Exchange Quotation. The shares of Partner Common
     Stock to be issued in the Merger shall have been approved for listing on
     the New York Stock Exchange.
                                       39
<PAGE>   143

SECTION 7.02  Additional Conditions to Obligations of Partner and Merger Sub.

     The obligations of Partner and Merger Sub to effect the Merger are subject
to the satisfaction of each of the following conditions, any of which may be
waived, in writing, exclusively by Partner and Merger Sub:

          (a) Representations and Warranties. The representations and warranties
     of Company set forth in this Agreement, disregarding any "materiality" or
     Company Material Adverse Effect qualifications set forth therein, shall be
     true and correct as of the date of this Agreement and (except to the extent
     such representations and warranties speak as of an earlier date) as of the
     Closing Date as though made on and as of the Closing Date, except (i) for
     changes contemplated by this Agreement and (ii) where the failures to be
     true and correct, individually or in the aggregate, do not have a Company
     Material Adverse Effect, or a material adverse effect upon the consummation
     of the transactions contemplated hereby.

          (b) Performance of Obligations of Company. Company shall have
     performed in all material respects all obligations required to be performed
     by it under this Agreement at or prior to the Closing Date; and Partner
     shall have received a certificate signed on behalf of Company by the chief
     executive officer and the chief financial officer of Company to such
     effect.

          (c) Tax Opinion. Partner shall have received a written opinion from
     Vinson & Elkins L.L.P., counsel to Partner, to the effect that the Merger
     will be treated for Federal income tax purposes as a tax-free
     reorganization within the meaning of Section 368(a) of the Internal Revenue
     Code; provided that if Vinson & Elkins L.L.P. does not render such opinion,
     this condition shall nonetheless be deemed satisfied if Brobeck, Phleger &
     Harrison LLP renders such opinion to Partner (it being agreed that Partner
     and Company shall each provide reasonable cooperation to Vinson & Elkins
     L.L.P. or Brobeck, Phleger & Harrison LLP, as the case may be, to enable
     them to render such opinion).

          (d) Pooling of Interests. Partner shall have received a written
     opinion, dated as of the Closing Date, from Arthur Andersen LLP, in form
     and substance reasonably satisfactory to Partner (the "Pooling Letter")
     that, based in part on Arthur Andersen LLP's concurrent written opinion
     (the "Pooling Entity Letter") that Company is a "poolable entity," the
     Merger, for financial accounting purposes, is a pooling of interests;
     provided, however, that the condition set forth in this Section 7.02(d)
     shall not apply if Partner is precluded from accounting for the Merger in
     accordance with the pooling of interests method of accounting solely by
     reason of an action taken by Partner or any of its Affiliates subsequent to
     the date of this Agreement other than any such action that is pursuant to
     the terms of, or contemplated by, this Agreement.

SECTION 7.03  Additional Conditions to Obligations of Company.

     The obligation of Company to effect the Merger is subject to the
satisfaction of each of the following conditions, any of which may be waived, in
writing, exclusively by Company:

          (a) Representations and Warranties. The representations and warranties
     of Partner and Merger Sub set forth in this Agreement, disregarding any
     "materiality" or Partner Material Adverse Effect qualifications set forth
     therein, shall be true and correct as of the date of this Agreement and
     (except to the extent such representations and warranties speak as of an
     earlier date) as of the Closing Date as though made on and as of the
     Closing Date, except (i) for changes contemplated by this Agreement and
     (ii) where the failures to be true and correct, individually or in the
     aggregate, do not have a Partner Material Adverse Effect, or a material
     adverse effect upon the consummation of the transactions contemplated
     hereby.

          (b) Performance of Obligations of Partner and Merger Sub. Partner and
     Merger Sub shall have performed in all material respects all obligations
     required to be performed by them under this Agreement at or prior to the
     Closing Date, and Company shall have received a certificate signed on
     behalf of Partner by the chief executive officer and the chief financial
     officer of Partner to such effect.

          (c) Tax Opinion. Company shall have received the opinion of Brobeck,
     Phleger & Harrison LLP, counsel to Company, to the effect that the Merger
     will be treated for Federal income tax purposes as a

                                       40
<PAGE>   144

     tax-free reorganization within the meaning of Section 368(a) of the
     Internal Revenue Code; provided that if Brobeck, Phleger & Harrison LLP
     does not render such opinion, this condition shall nonetheless be deemed
     satisfied if Vinson & Elkins L.L.P. renders such opinion to Company (it
     being agreed that Partner and Company shall each provide reasonable
     cooperation to Brobeck, Phleger & Harrison LLP or Vinson & Elkins L.L.P.,
     as the case may be, to enable them to render such opinion).

          (d) Pooling of Interests. Company shall have received the Pooling
     Letter, dated as of the Closing Date, from Arthur Andersen LLP that, based
     in part on Arthur Andersen LLP's Pooling Entity Letter that Company is a
     "poolable entity," the Merger, for financial accounting purposes, is a
     pooling of interests; provided, however, that the condition set forth in
     this Section 7.03(d) shall not apply if Partner is precluded from
     accounting for the Merger in accordance with the pooling of interests
     method of accounting solely by reason of an action taken by Company or any
     of its Affiliates subsequent to the date of this Agreement other than any
     such action that is pursuant to the terms of, or contemplated by, this
     Agreement.

                                 ARTICLE VIII.

                           TERMINATION AND AMENDMENT

SECTION 8.01  Termination.

     This Agreement may be terminated at any time prior to the Effective Time
(with respect to Section 8.01(b) through Section 8.01(g), by written notice by
the terminating party to the other party), whether before or after approval of
the matters presented in connection with the Merger by the stockholders of
Company or Partner:

          (a) by mutual written consent of Partner and Company; or

          (b) by either Partner or Company if the Merger shall not have been
     consummated by May 31, 2001 (the "Outside Date"); provided that the right
     to terminate this Agreement under this Section 8.01(b) shall not be
     available to any party whose failure to fulfill any obligation under this
     Agreement has been the cause of or resulted in the failure of the Merger to
     occur on or before such date; or

          (c) by either Partner or Company if a court of competent jurisdiction
     or other Governmental Entity shall have issued a nonappealable final order,
     decree or ruling or taken any other nonappealable final action, in each
     case having the effect of permanently enjoining or otherwise permanently
     prohibiting the Merger; or

          (d) by Partner or Company, if, at the Company Stockholders' Meeting
     (including any adjournment or postponement), the requisite vote of the
     stockholders of Company in favor of this Agreement and the Merger shall not
     have been obtained, or if, at the Partner Stockholders' Meeting (including
     any adjournment or postponement), the requisite vote of the stockholders of
     Partner in favor of the Partner Voting Proposal shall not have been
     obtained; or

          (e) by Partner, if (i) the Board of Directors of Company shall have
     withdrawn or modified, in a manner adverse to Partner, its recommendation
     of this Agreement or the Merger; (ii) the Board of Directors of Company
     shall have recommended to the stockholders of Company a Superior Proposal;
     or (iii) a tender offer or exchange offer for more than 35% of the
     outstanding shares of capital stock of Company is commenced and the Board
     of Directors of Company recommends in favor of the acceptance of such
     offer; or

          (f) by Company, if the Board of Directors of Partner shall have
     withdrawn or modified, in a manner adverse to Company, its recommendation
     of the Partner Voting Proposal; or

          (g) by Partner or Company, if there has been a breach of any
     representation, warranty, covenant or agreement on the part of the other
     party set forth in this Agreement, which breach (i) would, if uncured at
     Closing, cause the conditions set forth in Section 7.02(a) or Section
     7.02(b) (in the case of

                                       41
<PAGE>   145

     termination by Partner) or Section 7.03(a) or Section 7.03(b) (in the case
     of termination by Company) not to be satisfied, and (ii) shall not have
     been cured within twenty (20) business days following receipt by the
     breaching party of written notice of such breach from the other party.

SECTION 8.02  Effect of Termination.

     In the event of termination of this Agreement as provided in Section 8.01,
this Agreement shall, except as provided herein, immediately become void;
provided, upon such termination (i) the provisions of Section 6.12, this Section
8.02, Section 8.03 and Article IX of this Agreement and the Confidentiality
Agreement shall remain in full force and effect and survive any termination of
this Agreement, (ii) except as set forth in Section 6.12, this Section 8.02 and
Section 8.03, there shall be no liability or obligation on the part of Company,
Partner, Merger Sub or their respective officers, directors, stockholders or
Affiliates. Nothing in this Agreement shall relieve any party from liability for
the willful and knowing material breach of any of its representations,
warranties, covenants or agreements set forth in this Agreement. The rights and
remedies available to each party are expressly intended to be cumulative and may
be exercised singly or concurrently at such party's sole discretion.

SECTION 8.03  Fees and Expenses.

     (a) Except as set forth in this Section 8.03, all fees and expenses
incurred in connection with this Agreement and the transactions contemplated
hereby shall be paid by the party incurring such expenses, whether or not the
Merger is consummated, except that expenses incurred in connection with the
filing fee for the Joint Proxy Statement and printing and mailing the proxy
materials and the filing fee for the Merger under the HSR Act, if required,
shall be shared equally by Partner and Company.

     (b) Company shall pay Partner a termination fee of $15,000,000 upon the
earliest to occur of the following events:

          (i) the consummation by Company of, or the execution by Company of a
     definitive agreement providing for, an Acquisition Proposal within twelve
     (12) months after the termination of this Agreement by Partner or Company
     pursuant to Section 8.01(b) or Section 8.01(d) (for failure to obtain
     Company stockholder approval) if an Acquisition Proposal has been publicly
     announced and not subsequently abandoned or withdrawn prior to the date of
     termination, in the event of termination under Section 8.01(b), or the date
     of the Company Stockholders' Meeting, in the event of termination under
     Section 8.01(d); or

          (ii) the termination of this Agreement by Partner pursuant to Section
     8.01(e).

     (c) Partner shall pay Company a termination fee of $15,000,000 if this
Agreement is terminated by Company or Partner pursuant to Section 8.01(b) or
Section 8.01(d) (for failure to obtain Partner stockholder approval) if (i) a
Partner Acquisition Proposal has been publicly announced and not subsequently
abandoned or withdrawn prior to the date of termination, in the event of
termination under Section 8.01(b), or the date of the Partner Stockholders
Meeting, in the event of termination under Section 8.01(d), and (ii) such
Partner Acquisition Proposal is consummated, or Partner executes a definitive
agreement providing for such Partner Acquisition Proposal, within 12 months
after such termination;

     (d) The expenses and fees, if applicable, payable pursuant to Section
8.03(b) shall be paid by wire transfer within one business day after the first
to occur of the events described in Section 8.03(b)(i) or Section 8.03(b)(ii).
The expenses and fees, if applicable, payable pursuant to Section 8.03(c) shall
be paid by wire transfer within one business day after the consummation of the
Partner Acquisition Proposal referred to in Section 8.03(c)(ii).

SECTION 8.04  Amendment.

     This Agreement may be amended by the parties hereto, by action taken or
authorized by their respective Boards of Directors, at any time before or after
approval of the matters presented in connection with the

                                       42
<PAGE>   146

Merger by the stockholders of Company or of Partner, but, after any such
approval, no amendment shall be made which by law requires further approval by
such stockholders without such further approval. This Agreement may not be
amended except by an instrument in writing signed on behalf of each of the
parties hereto.

SECTION 8.05  Extension; Waiver.

     At any time prior to the Effective Time, the parties hereto, by action
taken or authorized by their respective Boards of Directors, may, to the extent
legally allowed, (i) extend the time for the performance of any of the
obligations or other acts of the other parties hereto, (ii) waive any
inaccuracies in the representations and warranties contained herein or in any
document delivered pursuant hereto and (iii) waive compliance with any of the
agreements or conditions contained herein. Any agreement on the part of a party
hereto to any such extension or waiver shall be valid only if set forth in a
written instrument signed on behalf of such party.

                                  ARTICLE IX.

                                 MISCELLANEOUS

SECTION 9.01  Nonsurvival of Representations, Warranties and Agreements.

     None of the representations, warranties and agreements in this Agreement or
in any instrument delivered pursuant to this Agreement shall survive the
Effective Time, except for the agreements contained in Section 1.04, Article II,
Section 6.11, Section 6.12, Section 6.13, Section 6.14, and Article IX, and the
agreements of the Affiliates delivered pursuant to Section 6.09. The
Confidentiality Agreement shall survive the execution and delivery of this
Agreement.

SECTION 9.02  Notices.

     All notices and other communications hereunder shall be in writing and
shall be deemed given if delivered personally, telecopied (which is confirmed)
or mailed by registered or certified mail (return receipt requested) to the
parties at the following addresses (or at such other address for a party as
shall be specified by like notice):

        (a) if to Partner or Merger Sub, to

            Stone Energy Corporation
            625 East Kaliste Saloom Road
            Lafayette, Louisiana 70508

            with a copy to:

            Vinson & Elkins L.L.P.
            1325 Avenue of the Americas
            New York, New York 10019
            Attention: Alan P. Baden
                       Eric S. Shube

            (b) if to Company, to

            Basin Exploration, Inc.
            1670 Broadway, Suite 2800
            Denver, Colorado 80202

                                       43
<PAGE>   147

        with a copy to

        Brobeck, Phleger & Harrison LLP
        370 Interlocken Boulevard
        Broomfield, Colorado 80021
        Attention: Paul Hilton

SECTION 9.03  Definitions.

     For purposes of this Agreement:

          (a) "Company Material Adverse Effect" means any change, effect, event,
     occurrence or state of facts that is or could reasonably be expected to be
     materially adverse to the business, properties, results of operations or
     condition (financial or otherwise) of Company and its Subsidiaries taken as
     a whole or that could reasonably be expected to materially impair the
     ability of Company to perform its obligations under this Agreement or to
     consummate the Merger; provided that none of the following, alone or in
     combination, shall constitute a Company Material Adverse Effect or be
     considered in determining whether a Company Material Adverse Effect has
     occurred or will occur: any change, effect, event, occurrence, state of
     facts or development arising out of, resulting from or relating to (i) the
     economy in general, (ii) the oil and gas exploration and production
     industry in general or in the Gulf of Mexico (including, without
     limitation, changes in commodity prices, general market prices and
     regulatory changes) or (iii) the transactions contemplated by this
     Agreement or the announcement thereof (provided, however, that with respect
     to any loss of personnel, this clause (iii) shall only be operative if
     management of Company provides Partner (if requested) with assurances
     reasonably acceptable to Partner that management of Company will undertake
     to furnish appropriate coverage for a reasonable transition period).

          (b) "Partner Material Adverse Effect" means any change, effect, event,
     occurrence or state of facts that is or could reasonably be expected to be
     materially adverse to the business, properties, results of operations or
     condition (financial or otherwise) of Partner and its Subsidiaries taken as
     a whole or that could reasonably be expected to materially impair the
     ability of Partner to perform its obligations under this Agreement or to
     consummate the Merger; provided that none of the following, alone or in
     combination, shall constitute a Partner Material Adverse Effect or be
     considered in determining whether a Partner Material Adverse Effect has
     occurred or will occur: any change, effect, event, occurrence, state of
     facts or development arising out of, resulting from or relating to (i) the
     economy in general or (ii) the oil and gas exploration and production
     industry in general or in the Gulf of Mexico (including, without
     limitation, changes in commodity prices, general market prices and
     regulatory changes).

          (c) "Partner Acquisition Proposal" shall mean any proposal or offer
     from a third party involving an acquisition of Partner, whether in the form
     of a tender offer for, or merger or other business combination with,
     Partner.

SECTION 9.04  Interpretation.

     When a reference is made in this Agreement to Sections, such reference
shall be to a Section of this Agreement unless otherwise indicated. The table of
contents and headings contained in this Agreement are for reference purposes
only and shall not affect in any way the meaning or interpretation of this
Agreement. Whenever the words "include," "includes" or "including" are used in
this Agreement they shall be deemed to be followed by the words "without
limitation." The phrase "made available" in this Agreement shall mean that the
information referred to has been made available if requested by the party to
whom such information is to be made available. The phrases "the date of this
Agreement," "the date hereof," and terms of similar import, unless the context
otherwise requires, shall be deemed to refer to October 28, 2000.

                                       44
<PAGE>   148

SECTION 9.05  Counterparts.

     This Agreement may be executed in two or more counterparts, all of which
shall be considered one and the same agreement and shall become effective when
two or more counterparts have been signed by each of the parties and delivered
to the other parties, it being understood that all parties need not sign the
same counterpart.

SECTION 9.06  Entire Agreement; No Third Party Beneficiaries.

     This Agreement (including the documents and the instruments referred to
herein) (a) constitutes the entire agreement and supersedes all prior agreements
and understandings, both written and oral, among the parties with respect to the
subject matter hereof, and (b) except as provided in Section 6.13 is not
intended to confer upon any person other than the parties hereto any rights or
remedies hereunder; provided that the Confidentiality Agreement shall remain in
full force and effect until the Effective Time. Each party hereto agrees that,
except for the representations and warranties contained in this Agreement and
its respective disclosure schedule, neither Company nor Partner makes any other
representations or warranties, and each hereby disclaims any other
representations and warranties made by itself or any of its officers, directors,
employees, agents, financial and legal advisors or other representatives, with
respect to the execution and delivery of this Agreement or the transactions
contemplated hereby, notwithstanding the delivery or disclosure to the other or
the other's representatives of any documentation or other information with
respect to any one or more of the foregoing.

SECTION 9.07  Governing Law.

     This Agreement shall be governed and construed in accordance with the laws
of the State of Delaware without regard to any applicable principles of
conflicts of law that would require the application of the laws of another
jurisdiction.

SECTION 9.08  Assignment.

     Neither this Agreement nor any of the rights, interests or obligations
hereunder shall be assigned by any of the parties hereto (whether by operation
of law or otherwise) without the prior written consent of the other parties;
provided, however, that Merger Sub may assign, in its sole discretion, any of or
all its rights, interests and obligations under this Agreement to Partner or to
any direct or indirect wholly-owned Subsidiary of Partner, but no such
assignment shall relieve Partner or Merger Sub of its obligations hereunder if
its transferee does not perform such obligations. Subject to the preceding
sentence, this Agreement will be binding upon, inure to the benefit of and be
enforceable by the parties and their respective successors and assigns.

SECTION 9.09  Severability.

     If any term or other provision of this Agreement is invalid, illegal or
incapable of being enforced by any rule or other applicable law, or public
policy, all other terms and provisions of this Agreement shall nevertheless
remain in full force and effect so long as the economic and legal substance of
the transactions contemplated hereby is not affected in any manner materially
adverse to any party. Upon such determination that any term or other provision
is invalid, illegal or incapable of being enforced, the parties hereto shall
negotiate in good faith to modify this Agreement so as to effect the original
intent of the parties as closely as possible in an acceptable manner to the end
that the transactions contemplated hereby are fulfilled to the extent possible;
provided, however, that nothing herein shall require any party to agree to any
modification that would affect the economic or legal substance of the
transactions contemplated hereby in any manner materially adverse to such party.

                                       45
<PAGE>   149

     IN WITNESS WHEREOF, Partner, Merger Sub and Company have caused this
Agreement to be signed by their respective officers thereunto duly authorized as
of the date first written above.

<TABLE>
<S>                                                    <C>
STONE ENERGY CORPORATION                               PARTNER ACQUISITION CORP.

By: /s/ D. PETER CANTY                                 By: /s/ D. PETER CANTY
    ----------------------------------------               ----------------------------------------

Title: President and Chief Operating Officer           Title: President and Chief Operating Officer
       -------------------------------------                  -------------------------------------


                                                       BASIN EXPLORATION, INC.

                                                       By: /s/ MICHAEL S. SMITH
                                                           ----------------------------------------

                                                       Title: Chief Executive Officer
                                                              -------------------------------------
</TABLE>

                                       46
<PAGE>   150

                                                          EXHIBIT A-1 TO ANNEX A

     COMPANY VOTING AGREEMENT (this "Agreement") dated as of October 28, 2000,
among Stone Energy Corporation, a Delaware corporation ("Partner"), Basin
Exploration, Inc., a Delaware corporation ("Company"), and the other parties
signatory hereto (each a "Stockholder").

     WHEREAS, each Stockholder desires that Company, Partner and Partner
Acquisition Corp., a Delaware corporation and wholly-owned subsidiary of Partner
("Merger Sub"), enter into an Agreement and Plan of Merger dated the date hereof
(as the same may be amended or supplemented, the "Merger Agreement"; capitalized
terms used but not defined herein shall have the meanings set forth in the
Merger Agreement) providing for the merger of Merger Sub with and into Company
(the "Merger") upon the terms and subject to the conditions set forth in the
Merger Agreement; and

     WHEREAS, each Stockholder and Company are executing this Agreement as an
inducement to Partner to enter into and execute, and to cause Merger Sub to
enter into and execute, the Merger Agreement;

     NOW, THEREFORE, in consideration of the execution and delivery by Partner
and Merger Sub of the Merger Agreement and the mutual covenants, conditions and
agreements contained herein and therein, the parties agree as follows:

     1. Representations and Warranties. (a) Each Stockholder severally
represents and warrants to Partner as follows:

          (i) Such Stockholder is the record and beneficial owner of, or is the
     sole trustee of a trust that is the record holder of, and whose
     beneficiaries are the beneficial owners of, the number of shares of common
     stock, par value $0.01 per share, of Company (the "Common Stock") set forth
     opposite such Stockholder's name on Schedule A hereto (such shares of
     Common Stock, together with any other shares of Common Stock or other
     capital stock of Company acquired after the date hereof (including through
     the exercise of any stock options, warrants or similar instruments) being
     collectively referred to herein as the "Subject Shares"). The Subject
     Shares constitute the only shares, with respect to which such Stockholder
     is the record or beneficial owner, of Common Stock, preferred stock or
     other capital stock of Company or options, warrants or other rights
     (whether or not contingent) to acquire such shares of capital stock of
     Company that are or may be entitled to vote on the Merger or the Merger
     Agreement at any meeting of stockholders of Company called to vote upon the
     Merger or the Merger Agreement. Such Stockholder has the sole right to vote
     and Transfer (as defined below in Section 3(a)) the Subject Shares set
     forth opposite its name on Schedule A hereto, and none of such Subject
     Shares is subject to any voting trust or other agreement, arrangement or
     restriction with respect to the voting or the Transfer of the Subject
     Shares, except as provided by this Agreement (it being understood that any
     pledge of the Pledged Shares (as defined below) shall not be a breach of
     this representation). Such Stockholder has all requisite power and
     authority, and, if such Stockholder is a natural person, the legal
     capacity, to enter into this Agreement and to perform its obligations
     hereunder. To the extent that such Stockholder is an entity and not an
     individual, such Stockholder is duly organized, validly existing and in
     good standing under the laws of its jurisdiction of organization. The
     execution and delivery of this Agreement by such Stockholder and the
     performance by such Stockholder of its obligations hereunder have been duly
     authorized by all necessary action on the part of such Stockholder. This
     Agreement has been duly executed and delivered by, and constitutes a valid
     and binding agreement of, such Stockholder, enforceable against such
     Stockholder in accordance with its terms, except as enforcement may be
     limited by bankruptcy, insolvency, moratorium or other similar laws and
     except that the availability of equitable remedies, including specific
     performance, is subject to the discretion of the court before which any
     proceeding for such remedy may be brought (collectively, the "Bankruptcy
     and Equity Exceptions").

          (ii) Neither the execution and delivery of this Agreement nor the
     performance by such Stockholder of its obligations hereunder will result in
     a violation of, or a default under, or conflict with, (A) if such
     Stockholder is an entity, any provision of its certificate of
     incorporation, bylaws,
                                      A-1-1
<PAGE>   151

     partnership agreement, limited liability company agreement or similar
     organizational documents, (B) any contract, trust, commitment, agreement,
     understanding, arrangement or restriction of any kind (other than as may
     relate to the Pledged Shares but subject to the proviso set forth in (iv)
     below) to which such Stockholder is a party or bound or to which the
     Subject Shares are subject, except, in the case of clause (B) above, as
     would not prevent, delay or otherwise materially impair such Stockholder's
     ability to perform its obligations hereunder. Execution, delivery and
     performance of this Agreement by such Stockholder will not reasonably be
     expected to violate, or require any consent, approval or notice under, any
     provision of any judgment, order, decree, statute, law, rule or regulation
     applicable to such Stockholder or the Subject Shares, except (x) for any
     necessary filing under the Hart-Scott-Rodino Antitrust Improvements Act of
     1976, (y) for any reports under Sections 13(d) and 16 of the Exchange Act
     as may be required in connection with this Agreement and the transactions
     contemplated hereby or (z) as would not reasonably be expected to prevent,
     delay or otherwise materially impair such Stockholder's ability to perform
     its obligations hereunder.

          (iii) If the Stockholder is married and the Subject Shares of the
     Stockholder constitute community property or spousal approval is otherwise
     required for this Agreement to be legal, valid and binding, then, to the
     extent so required, this Agreement has been duly authorized, executed and
     delivered by, and constitutes a valid and binding agreement of, the
     Stockholder's spouse, enforceable against such spouse in accordance with
     its terms, subject to the Bankruptcy and Equity Exceptions. Except for any
     consents duly obtained as of the date hereof and which will remain in full
     force and effect at such time or times as may be necessary to duly consent
     to such Stockholder's performance of its obligations hereunder, no trust of
     which such Stockholder is a trustee requires the consent of any beneficiary
     to the execution and delivery of this Agreement or to the performance by
     such Stockholder of its obligations hereunder.

          (iv) The Subject Shares and the certificates representing such Shares
     are held by such Stockholder, or by a nominee or custodian for the benefit
     of such Stockholder, free and clear of all liens, claims, security
     interests, proxies, voting trusts or agreements, understandings or
     arrangements or any other encumbrances whatsoever, except for (A) any such
     encumbrances or proxies arising hereunder or under the existing terms of a
     trust of which such Stockholder is the trustee or (B) any such encumbrances
     arising pursuant to the pledge of any Subject Shares by such Stockholder
     prior to the date hereof to a financial institution or a brokerage firm
     (the "Pledged Shares"); provided, however, that such Stockholder represents
     that any such arrangement regarding such Pledged Shares shall not prevent,
     delay or otherwise materially impair such Stockholder's ability to execute
     and deliver this Agreement or perform its obligations hereunder and such
     Stockholder shall use his reasonable efforts to obtain an acknowledgment by
     the pledgee of the terms of this Agreement and such pledgee's agreement to
     execute a proxy or to otherwise vote the Pledged Shares (if and to the
     extent the voting power of the Pledged Shares is being or to be exercised
     by pledgee) in accordance with Section 2 hereof.

          (v) No broker, investment banker, financial advisor or other person is
     entitled to any broker's, finder's, financial advisor's or other similar
     fee or commission based upon arrangements made by or on behalf of such
     Stockholder in connection with its entering into this Agreement.

          (vi) Such Stockholder understands and acknowledges that Partner is
     entering into, and causing Merger Sub to enter into, the Merger Agreement
     in reliance upon such Stockholder's execution and delivery of this
     Agreement.

     (b) Partner represents and warrants to each Stockholder that the execution
and delivery of this Agreement by Partner and the consummation by Partner of the
transactions contemplated hereby have been duly authorized by all necessary
action on the part of Partner.

     2. Voting Agreements. Each Stockholder severally agrees with, and covenants
to, Partner that, during the Term (as defined below) of this Agreement, at any
meeting of stockholders of Company called to vote
                                      A-1-2
<PAGE>   152

upon the Merger and the Merger Agreement or at any adjournment thereof or in any
other circumstances upon which a vote, consent or other approval (including by
written consent) with respect to the Merger and the Merger Agreement is sought,
such Stockholder shall, including by executing a written consent solicitation if
requested by Partner, vote (or cause to be voted) the Subject Shares in favor of
the Merger, the adoption by Company of the Merger Agreement and the approval of
the terms thereof and each of the other transactions expressly contemplated by
the Merger Agreement.

     3. Other Covenants. Each Stockholder severally agrees with, and covenants
to, Partner during the Term of this Agreement as follows:

          (a) Such Stockholder shall not after the date hereof (i) sell,
     transfer, pledge, assign or otherwise dispose of (including by gift)
     (collectively, "Transfer"), or consent to any Transfer of, any Subject
     Shares or any interest therein, except pursuant to the Merger, (ii) enter
     into any contract, option or other agreement with respect to any Transfer
     of any or all of the Subject Shares or any interest therein, (iii) grant
     any proxy, power-of-attorney or other authorization in or with respect to
     the Subject Shares, except for this Agreement or (iv) deposit the Subject
     Shares into a voting trust or enter into a voting agreement or voting
     arrangement with respect to the Subject Shares; provided, that any such
     Stockholder may (x) Transfer any of the Subject Shares to any other
     Stockholder who is on the date hereof a party to this Agreement, or to any
     other person or entity that, prior to or coincident with such Transfer,
     executes an irrevocable proxy to vote such Subject Shares in accordance
     with Section 2 and (y) Transfer a de minimus amount of such Subject Shares
     (which in the case of Mr. Michael Smith, shall include Transfers up to
     75,000 shares in the aggregate); provided, however, that such Stockholder
     shall not transfer any Subject Shares pursuant to the preceding proviso (i)
     without Partner's prior written consent, not to be unreasonably withheld or
     delayed and (ii) if any such transfer, either alone or in the aggregate
     with other transfers by Stockholders and other persons who may be
     affiliates of Company, would preclude Partner's ability to account for the
     business combination to be effected by the Merger as a pooling of
     interests; provided, further the foregoing restrictions shall not be deemed
     violated in the event of any action taken by the pledgee of any Pledged
     Shares pursuant to the terms of any agreements existing as of the date
     hereof with respect thereto so long as such Stockholder uses his reasonable
     efforts to obtain an acknowledgment by the pledgee of the terms of this
     Agreement and such pledgee's agreement to execute a proxy or to otherwise
     vote the Pledged Shares (if and to the extent the voting power of the
     Pledged Shares is being or to be exercised by pledgee) in accordance with
     Section 2 hereof; provided, further, that the restrictions in this Section
     3 shall not be deemed violated by any Transfer of Subject Shares pursuant
     to a cashless exercise of stock options.

          (b) Such Stockholder hereby waives any rights of appraisal, or rights
     to dissent from the Merger, that such Stockholder may have.

          (c) Such Stockholder shall not take any action prohibited by Section
     6.01 of the Merger Agreement.

     4. Certain Events. Each Stockholder agrees that this Agreement and the
obligations hereunder shall attach to such Stockholder's Subject Shares and
shall be binding upon any person or entity to which legal or beneficial
ownership of such Shares shall pass, whether by operation of law or otherwise,
including without limitation such Stockholder's heirs, guardians, administrators
or successors. In the event of any stock split, stock dividend, merger,
reorganization, recapitalization or other change in the capital structure of
Company affecting the Common Stock, preferred stock or the acquisition of
additional shares of Common Stock, preferred stock or other voting securities of
Company by any Stockholder, the number of Shares listed on Schedule A beside the
name of such Stockholder shall be adjusted appropriately and this Agreement and
the obligations hereunder shall attach to any additional shares of Common Stock,
preferred stock or other voting securities of Company issued to or acquired by
such Stockholder.

                                      A-1-3
<PAGE>   153

     5. Stop Transfer. Company agrees with, and covenants to, Partner that
Company shall not register the transfer of any certificate representing any
Subject Shares, unless such transfer is made to Partner or Merger Sub or
otherwise in compliance with this Agreement.

     6. Stockholder Capacity. No person executing this Agreement who is or
becomes during the term hereof a director of Company makes any agreement or
understanding herein in his or her capacity as such director. Each Stockholder
signs solely in his or her capacity as the record and beneficial owner of, or
the trustee of a trust whose beneficiaries are the beneficial owners of, such
Stockholder's Subject Shares.

     7. Further Assurances. Each Stockholder shall, upon request of Partner,
execute and deliver any additional documents and take such further actions as
may reasonably be deemed by Partner to be necessary or desirable to carry out
the provisions hereof.

     8. Termination. This Agreement, and all rights and obligations of the
parties hereunder, shall terminate upon (and shall only be effective from the
date hereof until) the first to occur of (the "Term") (i) the Effective Time of
the Merger or (ii) the date upon which the Merger Agreement is terminated in
accordance with its terms; provided, however, that (x) Section 9 shall survive
any termination of this Agreement and (y) termination of this Agreement pursuant
to Clause (ii) above shall not relieve any party hereto from liability for any
willful and knowing breach hereof prior to such termination.

     9. Miscellaneous.

     (a) All notices, requests, claims, demands and other communications under
this Agreement shall be in writing and shall be deemed given if delivered
personally or sent by overnight courier (providing proof of delivery) to the
parties at the following addresses (or at such other address for a party as
shall be specified by like notice): (i) if to Partner or Company, to the
appropriate address set forth in Section 9.02 of the Merger Agreement; and (ii)
if to a Stockholder, to the appropriate address set forth on Schedule A hereto.

     (b) The headings contained in this Agreement are for reference purposes
only and shall not affect in any way the meaning or interpretation of this
Agreement.

     (c) This Agreement may be executed in two or more counterparts, all of
which shall be considered one and the same agreement and shall become effective
as to any Stockholder when one or more counterparts have been signed by each of
Partner, Company and such Stockholder and delivered to Partner, Company and such
Stockholder.

     (d) This Agreement (including the documents and instruments referred to
herein) constitutes the entire agreement, and supersedes all prior agreements
and understandings, both written and oral, among the parties with respect to the
subject matter hereof, and this Agreement is not intended to confer upon any
other person (other than Merger Sub) any rights or remedies hereunder.

     (e) This Agreement shall be governed by, and construed in accordance with,
the laws of the State of Delaware, regardless of the laws that might otherwise
govern under applicable principles of conflicts of laws thereof.

     (f) Neither this Agreement nor any of the rights, interests or obligations
under this Agreement shall be assigned, in whole or in part, by operation of law
or otherwise, by any of the parties without the prior written consent of the
other parties, except by laws of descent or as expressly provided by Section
3(a). Any assignment in violation of the foregoing shall be void.

     (g) As between any Stockholder and Company, each of such parties agrees
that irreparable damage to the other, non-breaching party would occur and that
such non-breaching party would not have any adequate remedy at law in the event
that any of the provisions of this Agreement were not performed in accordance
with their specific terms or were otherwise breached. It is accordingly agreed
that the non-breaching party shall be entitled to an injunction or injunctions
to prevent breaches by the other party of this Agreement and to enforce
specifically the terms and provisions of this Agreement in any Federal court
located in the State of Delaware or in any Delaware state court, this being in
addition to any other remedy

                                      A-1-4
<PAGE>   154

to which it may be entitled at law or in equity. In addition, each of the
parties hereto (i) consents to submit such party to the personal jurisdiction of
any Federal court located in the State of Delaware or any Delaware state court
in the event any dispute arises out of this Agreement or any of the transactions
contemplated hereby and (ii) agrees that such party will not attempt to deny or
defeat such personal jurisdiction by motion or other request for leave from any
such court.

     (h) If any term, provision, covenant or restriction herein, or the
application thereof to any circumstance, shall, to any extent, be held by a
court of competent jurisdiction to be invalid, void or unenforceable, the
remainder of the terms, provisions, covenants and restrictions herein and the
application thereof to any other circumstances shall remain in full force and
effect, shall not in any way be affected, impaired or invalidated, and shall be
enforced to the fullest extent permitted by law.

     (i) No amendment, modification or waiver in respect of this Agreement shall
be effective against any party unless it shall be in writing and signed by such
party.

               [Remainder of this page intentionally left blank]

                                      A-1-5
<PAGE>   155

     IN WITNESS WHEREOF, Stone Energy Corporation, Basin Exploration, Inc. and
the Stockholders party hereto have caused this Agreement to be duly executed and
delivered as of the date first written above.

                                            STONE ENERGY CORPORATION

                                            By:
                                              ----------------------------------
                                              Name:
                                              Title:

                                            BASIN EXPLORATION, INC.

                                            By:
                                              ----------------------------------
                                              Name:
                                              Title:

                                            ------------------------------------
                                            Name: MICHAEL S. SMITH

                                            ------------------------------------
                                            Name: NEIL L. STENBUCK

                                            ------------------------------------
                                            Name: HOWARD L. BOIGON

                                            ------------------------------------
                                            Name: DONALD H. ANDERSON

                                            ------------------------------------
                                            Name: JOHN F. GREENE

                                            ------------------------------------
                                            Name: J. PAUL HELLSTROM

                                            ------------------------------------
                                            Name: MICHAEL A. NICOLAIS

                                            ------------------------------------
                                            Name: LARRY D. UNRUH
                                      A-1-6
<PAGE>   156

                                                          EXHIBIT A-2 TO ANNEX A

     PARTNER VOTING AGREEMENT (this "Agreement") dated as of October 28, 2000,
among Stone Energy Corporation, a Delaware corporation ("Partner"), Basin
Exploration, Inc., a Delaware corporation ("Company"), and the other parties
signatory hereto (each a "Stockholder").

     WHEREAS, each Stockholder desires that Company, Partner and Partner
Acquisition Corp., a Delaware corporation and wholly-owned subsidiary of Partner
("Merger Sub"), enter into an Agreement and Plan of Merger dated the date hereof
(as the same may be amended or supplemented, the "Merger Agreement"; capitalized
terms used but not defined herein shall have the meanings set forth in the
Merger Agreement) providing for the merger of Merger Sub with and into Company
(the "Merger") upon the terms and subject to the conditions set forth in the
Merger Agreement; and

     WHEREAS, each Stockholder and Partner are executing this Agreement as an
inducement to Company to enter into and execute the Merger Agreement;

     NOW, THEREFORE, in consideration of the execution and delivery by Company
of the Merger Agreement and the mutual covenants, conditions and agreements
contained herein and therein, the parties agree as follows:

     1. Representations and Warranties.  (a) Each Stockholder severally
represents and warrants to Company as follows:

          (i) Such Stockholder is the record and beneficial owner of, or is the
     sole trustee of a trust that is the record holder of, and whose
     beneficiaries are the beneficial owners of, the number of shares of common
     stock, par value $0.01 per share, of Partner (the "Common Stock") set forth
     opposite such Stockholder's name on Schedule A hereto (such shares of
     Common Stock, together with any other shares of Common Stock or other
     capital stock of Partner acquired after the date hereof (including through
     the exercise of any stock options, warrants or similar instruments) being
     collectively referred to herein as the "Subject Shares"). The Subject
     Shares constitute the only shares, with respect to which such Stockholder
     is the record or beneficial owner, of Common Stock, preferred stock or
     other capital stock of Partner or options, warrants or other rights
     (whether or not contingent) to acquire such shares of capital stock of
     Partner that are or may be entitled to vote on the amendment of Partner's
     certification of incorporation and the issuance of Partner's shares of
     Common Stock in connection with the Merger at any meeting of stockholders
     of Partner called to vote upon the amendment of Partner's certification of
     incorporation and the issuance of Partner's shares of Common Stock in
     connection with the Merger. Such Stockholder has the sole right to vote and
     Transfer (as defined below in Section 3(a)) the Subject Shares set forth
     opposite its name on Schedule A hereto, and none of such Subject Shares is
     subject to any voting trust or other agreement, arrangement or restriction
     with respect to the voting or the Transfer of the Subject Shares, except as
     provided by this Agreement (it being understood that any pledge of the
     Pledged Shares (as defined below) shall not be a breach of this
     representation). Such Stockholder has all requisite power and authority,
     and, if such Stockholder is a natural person, the legal capacity, to enter
     into this Agreement and to perform its obligations hereunder. To the extent
     that such Stockholder is an entity and not an individual, such Stockholder
     is duly organized, validly existing and in good standing under the laws of
     its jurisdiction of organization. The execution and delivery of this
     Agreement by such Stockholder and the performance by such Stockholder of
     its obligations hereunder have been duly authorized by all necessary action
     on the part of such Stockholder. This Agreement has been duly executed and
     delivered by, and constitutes a valid and binding agreement of, such
     Stockholder, enforceable against such Stockholder in accordance with its
     terms, except as enforcement may be limited by bankruptcy, insolvency,
     moratorium or other similar laws and except that the availability of
     equitable remedies, including specific performance, is subject to the
     discretion of the court before which any proceeding for such remedy may be
     brought (collectively, the "Bankruptcy and Equity Exceptions").

          (ii) Neither the execution and delivery of this Agreement nor the
     performance by such Stockholder of its obligations hereunder will result in
     a violation of, or a default under, or conflict
                                      A-2-1
<PAGE>   157

     with, (A) if such Stockholder is an entity, any provision of its
     certificate of incorporation, bylaws, partnership agreement, limited
     liability company agreement or similar organizational documents, (B) any
     contract, trust, commitment, agreement, understanding, arrangement or
     restriction of any kind (other than as may relate to the Pledged Shares but
     subject to the proviso set forth in (iv) below) to which such Stockholder
     is a party or bound or to which the Subject Shares are subject, except, in
     the case of clause (B) above, as would not prevent, delay or otherwise
     materially impair such Stockholder's ability to perform its obligations
     hereunder. Execution, delivery and performance of this Agreement by such
     Stockholder will not reasonably be expected to violate, or require any
     consent, approval or notice under, any provision of any judgment, order,
     decree, statute, law, rule or regulation applicable to such Stockholder or
     the Subject Shares, except (x) for any necessary filing under the
     Hart-Scott-Rodino Antitrust Improvements Act of 1976, (y) for any reports
     under Sections 13(d) and 16 of the Exchange Act as may be required in
     connection with this Agreement and the transactions contemplated hereby or
     (z) as would not reasonably be expected to prevent, delay or otherwise
     materially impair such Stockholder's ability to perform its obligations
     hereunder.

          (iii) If the Stockholder is married and the Subject Shares of the
     Stockholder constitute community property or spousal approval is otherwise
     required for this Agreement to be legal, valid and binding, then, to the
     extent so required, this Agreement has been duly authorized, executed and
     delivered by, and constitutes a valid and binding agreement of, the
     Stockholder's spouse, enforceable against such spouse in accordance with
     its terms, subject to the Bankruptcy and Equity Exceptions. Except for any
     consents duly obtained as of the date hereof and which will remain in full
     force and effect at such time or times as may be necessary to duly consent
     to such Stockholder's performance of its obligations hereunder, no trust of
     which such Stockholder is a trustee requires the consent of any beneficiary
     to the execution and delivery of this Agreement or to the performance by
     such Stockholder of its obligations hereunder.

          (iv) The Subject Shares and the certificates representing such Shares
     are held by such Stockholder, or by a nominee or custodian for the benefit
     of such Stockholder, free and clear of all liens, claims, security
     interests, proxies, voting trusts or agreements, understandings or
     arrangements or any other encumbrances whatsoever, except for (A) any such
     encumbrances or proxies arising hereunder or under the existing terms of a
     trust of which such Stockholder is the trustee or (B) any such encumbrances
     arising pursuant to the pledge of any Subject Shares by such Stockholder
     prior to the date hereof to a financial institution or a brokerage firm
     (the "Pledged Shares"); provided, however, that such Stockholder represents
     that any such arrangement regarding such Pledged Shares shall not prevent,
     delay or otherwise materially impair such Stockholder's ability to execute
     and deliver this Agreement or perform its obligations hereunder and such
     Stockholder shall use his reasonable efforts to obtain an acknowledgment by
     the pledgee of the terms of this Agreement and such pledgee's agreement to
     execute a proxy or to otherwise vote the Pledged Shares (if and to the
     extent the voting power of the Pledged Shares is being or to be exercised
     by pledgee) in accordance with Section 2 hereof.

          (v) No broker, investment banker, financial advisor or other person is
     entitled to any broker's, finder's, financial advisor's or other similar
     fee or commission based upon arrangements made by or on behalf of such
     Stockholder in connection with its entering into this Agreement.

          (vi) Such Stockholder understands and acknowledges that Company is
     entering into the Merger Agreement in reliance upon such Stockholder's
     execution and delivery of this Agreement.

     (b) Company represents and warrants to each Stockholder that the execution
and delivery of this Agreement by Company and the consummation by Company of the
transactions contemplated hereby have been duly authorized by all necessary
action on the part of Company.

     2. Voting Agreements. Each Stockholder severally agrees with, and covenants
to, Company that, during the Term (as defined below) of this Agreement, at any
meeting of stockholders of Partner called to

                                      A-2-2
<PAGE>   158

vote upon the amendment of Partner's certificate of incorporation and the
issuance of shares of Partner Common Stock in connection with the consummation
of the Merger or at any adjournment thereof or in any other circumstances upon
which a vote, consent or other approval (including by written consent) with
respect to the amendment of Partner's certificate of incorporation and the
issuance of shares of Partner Common Stock in connection with the consummation
of the Merger is sought, such Stockholder shall, including by executing a
written consent solicitation if requested by Company, vote (or cause to be
voted) the Subject Shares in favor of the amendment of Partner's certificate of
incorporation and the issuance of shares of Partner Common Stock in connection
with the consummation of the Merger.

     3. Other Covenants. Each Stockholder severally agrees with, and covenants
to, Company during the Term of this Agreement as follows:

          (a) Such Stockholder shall not after the date hereof (i) sell,
     transfer, pledge, assign or otherwise dispose of (including by gift)
     (collectively, "Transfer"), or consent to any Transfer of, any Subject
     Shares or any interest therein, (ii) enter into any contract, option or
     other agreement with respect to any Transfer of any or all of the Subject
     Shares or any interest therein, (iii) grant any proxy, power-of-attorney or
     other authorization in or with respect to the Subject Shares, except for
     this Agreement or (iv) deposit the Subject Shares into a voting trust or
     enter into a voting agreement or voting arrangement with respect to the
     Subject Shares; provided, that any such Stockholder may (x) Transfer any of
     the Subject Shares to any other Stockholder who is on the date hereof a
     party to this Agreement, or to any other person or entity that, prior to or
     coincident with such Transfer, executes an irrevocable proxy to vote such
     Subject Shares in accordance with Section 2 and (y) Transfer a de minimus
     amount of such Subject Shares (which in the case of Mr. James Stone, shall
     include Transfers up to 75,000 shares in the aggregate); provided, however,
     that such Stockholder shall not transfer any Subject Shares pursuant to the
     preceding proviso if any such transfer, either alone or in the aggregate
     with other transfers by Stockholders and other persons who may be
     affiliates of Company, would preclude Partner's ability to account for the
     business combination to be effected by the Merger as a pooling of
     interests; provided, further the foregoing restrictions shall not be deemed
     violated in the event of any action taken by the pledgee of any Pledged
     Shares pursuant to the terms of any agreements existing as of the date
     hereof with respect thereto so long as such Stockholder uses his reasonable
     efforts to obtain an acknowledgment by the pledgee of the terms of this
     Agreement and such pledgee's agreement to execute a proxy or to otherwise
     vote the Pledged Shares (if and to the extent the voting power of the
     Pledged Shares is being or to be exercised by pledgee) in accordance with
     Section 2 hereof; provided, further, that the restrictions in this Section
     3 shall not be deemed violated by any Transfer of Subject Shares pursuant
     to a cashless exercise of stock options; and

          (b) Such Stockholder (in his capacity as such) shall not, nor shall it
     permit any investment banker, attorney or other adviser or representative
     of such Stockholder (in his capacity as such) to, directly or indirectly,
     (i) solicit, initiate or encourage the submission of, any Partner
     Acquisition Proposal or (ii) participate in any discussions or negotiations
     regarding, or furnish to any person any information with respect to, or
     take any other action to facilitate any inquires or the making of any
     proposal that constitutes, or may reasonably be expected to lead to, any
     Partner Acquisition Proposal; provided, however, that nothing herein shall
     prohibit any Stockholder that is an officer or director of Partner from
     taking any action that Partner (or that such Stockholder in his capacity as
     an officer or director of Partner) would be permitted to take under the
     terms of the Merger Agreement.

     4. Certain Events. Each Stockholder agrees that this Agreement and the
obligations hereunder shall attach to such Stockholder's Subject Shares and
shall be binding upon any person or entity to which legal or beneficial
ownership of such Shares shall pass, whether by operation of law or otherwise,
including without limitation such Stockholder's heirs, guardians, administrators
or successors. In the event of any stock split, stock dividend, merger,
reorganization, recapitalization or other change in the capital structure of
Partner affecting the Common Stock, preferred stock or the acquisition of
additional shares of Common Stock, preferred stock or other voting securities of
Partner by any Stockholder, the number of Shares listed

                                      A-2-3
<PAGE>   159

on Schedule A beside the name of such Stockholder shall be adjusted
appropriately and this Agreement and the obligations hereunder shall attach to
any additional shares of Common Stock, preferred stock or other voting
securities of Partner issued to or acquired by such Stockholder.

     5. Stop Transfer. Partner agrees with, and covenants to, Company that
Partner shall not register the transfer of any certificate representing any
Subject Shares, unless such transfer is in compliance with this Agreement.

     6. Stockholder Capacity. No person executing this Agreement who is or
becomes during the term hereof a director of Partner makes any agreement or
understanding herein in his or her capacity as such director. Each Stockholder
signs solely in his or her capacity as the record and beneficial owner of, or
the trustee of a trust whose beneficiaries are the beneficial owners of, such
Stockholder's Subject Shares.

     7. Further Assurances. Each Stockholder shall, upon request of Company,
execute and deliver any additional documents and take such further actions as
may reasonably be deemed by Company to be necessary or desirable to carry out
the provisions hereof.

     8. Termination. This Agreement, and all rights and obligations of the
parties hereunder, shall terminate upon (and shall only be effective from the
date hereof until) the first to occur of (the "Term") (i) the Effective Time of
the Merger or (ii) the date upon which the Merger Agreement is terminated in
accordance with its terms; provided, however, that (x) Section 9 shall survive
any termination of this Agreement pursuant to clause (ii) above and (y)
termination of this Agreement shall not relieve any party hereto from liability
for any willful and knowing breach hereof prior to such termination.

     9. Miscellaneous.

     (a) All notices, requests, claims, demands and other communications under
this Agreement shall be in writing and shall be deemed given if delivered
personally or sent by overnight courier (providing proof of delivery) to the
parties at the following addresses (or at such other address for a party as
shall be specified by like notice): (i) if to Partner or Company, to the
appropriate address set forth in Section 9.02 of the Merger Agreement; and (ii)
if to a Stockholder, to the appropriate address set forth on Schedule A hereto.

     (b) The headings contained in this Agreement are for reference purposes
only and shall not affect in any way the meaning or interpretation of this
Agreement.

     (c) This Agreement may be executed in two or more counterparts, all of
which shall be considered one and the same agreement and shall become effective
as to any Stockholder when one or more counterparts have been signed by each of
Partner, Company and such Stockholder and delivered to Partner, Company and such
Stockholder.

     (d) This Agreement (including the documents and instruments referred to
herein) constitutes the entire agreement, and supersedes all prior agreements
and understandings, both written and oral, among the parties with respect to the
subject matter hereof, and this Agreement is not intended to confer upon any
other person any rights or remedies hereunder.

     (e) This Agreement shall be governed by, and construed in accordance with,
the laws of the State of Delaware, regardless of the laws that might otherwise
govern under applicable principles of conflicts of laws thereof.

     (f) Neither this Agreement nor any of the rights, interests or obligations
under this Agreement shall be assigned, in whole or in part, by operation of law
or otherwise, by any of the parties without the prior written consent of the
other parties, except by laws of descent or as expressly provided by Section
3(a). Any assignment in violation of the foregoing shall be void.

     (g) As between any Stockholder and Partner, each of such parties agrees
that irreparable damage to the other, non-breaching party would occur and that
such non-breaching party would not have any adequate remedy at law in the event
that any of the provisions of this Agreement were not performed in accordance
with their specific terms or were otherwise breached. It is accordingly agreed
that the non-
                                      A-2-4
<PAGE>   160

breaching party shall be entitled to an injunction or injunctions to prevent
breaches by the other party of this Agreement and to enforce specifically the
terms and provisions of this Agreement in any Federal court located in the State
of Delaware or in any Delaware state court, this being in addition to any other
remedy to which it may be entitled at law or in equity. In addition, each of the
parties hereto (i) consents to submit such party to the personal jurisdiction of
any Federal court located in the State of Delaware or any Delaware state court
in the event any dispute arises out of this Agreement or any of the transactions
contemplated hereby and (ii) agrees that such party will not attempt to deny or
defeat such personal jurisdiction by motion or other request for leave from any
such court.

     (h) If any term, provision, covenant or restriction herein, or the
application thereof to any circumstance, shall, to any extent, be held by a
court of competent jurisdiction to be invalid, void or unenforceable, the
remainder of the terms, provisions, covenants and restrictions herein and the
application thereof to any other circumstances shall remain in full force and
effect, shall not in any way be affected, impaired or invalidated, and shall be
enforced to the fullest extent permitted by law.

     (i) No amendment, modification or waiver in respect of this Agreement shall
be effective against any party unless it shall be in writing and signed by such
party.

                                      A-2-5
<PAGE>   161

     IN WITNESS WHEREOF, Stone Energy Corporation, Basin Exploration, Inc. and
the Stockholders party hereto have caused this Agreement to be duly executed and
delivered as of the date first written above.

                                            STONE ENERGY CORPORATION

                                            By:
                                              ----------------------------------
                                              Name:
                                              Title:

                                            BASIN EXPLORATION, INC.

                                            By:
                                              ----------------------------------
                                              Name:
                                              Title:

                                            ------------------------------------
                                            Name: JAMES H. STONE

                                            ------------------------------------
                                            Name: D. PETER CANTY

                                            ------------------------------------
                                            Name: RAYMOND B. GARY

                                            ------------------------------------
                                            Name: DAVID R. VOELKER

                                            ------------------------------------
                                            Name: PETER K. BARKER

                                            ------------------------------------
                                            Name: B.J. DUPLANTIS

                                            ------------------------------------
                                            Name: JOHN P. LABORDE

                                            ------------------------------------
                                            Name: ROBERT A. BERNHARD

                                            ------------------------------------
                                            Name: JOE R. KLUTTS

                                      A-2-6
<PAGE>   162

                                                     APPENDIX 1.04(C) TO ANNEX A

                           NON-COMPETITION TERM SHEET

     1. Subject to customary exceptions, Smith will not disclose or furnish to
anyone any confidential and proprietary information about Basin and/or Stone and
their prospects or use such information for his own benefit or the benefit of
any other person.

     2. The territory covered by the non-competition restrictions to be set
forth in the confidentiality and non-competition agreement (the "Agreement")
shall be limited to those properties (as to all depths from the surface of the
earth down to the center of the earth) in the Gulf of Mexico, Louisiana, Texas,
Colorado, Utah and Wyoming that are, as of the Effective Time, either (i)
covered by one or more mineral leases in which Stone and/or Basin have a right,
title or interest or (ii) shown on one or more maps or geological or geophysical
interpretations of Stone and/or Basin to be prospect areas as that term is used
generally in the oil and gas business, which are known to Michael S. Smith as of
the date hereof.

     3. The consideration for the non-competition and confidentiality
restrictions will be Stone's agreement to acquire Basin (pursuant to which Smith
will receive significant value in the form of Stone Common Stock) and, as
additional consideration for the non-competition restrictions, Stone's agreement
to pay Smith the sum of Three Hundred Thousand and No/100 ($300,000.00) Dollars
per year, which shall be paid to Smith monthly in arrears, for each of the three
years following the Effective Time.

     4. The Agreement will also include such other terms, provisions and
exceptions as are customary for agreements of this sort, to the extent the same
are mutually agreeable to Smith and Stone.

     5. The Agreement will be governed by New York law.

     6. The Agreement will be effective at the Effective Time, subject to
Michael S. Smith's continued employment with Basin as of the Effective Time, it
being agreed that Michael S. Smith will not voluntarily terminate his employment
with Basin prior to such time.

     7. In order to ensure that Stone will have an adequate period of time to
assemble a management team for the transition in the event that the Effective
Time occurs prior to February 28, 2001, Stone will cause Basin to retain Michael
Smith as an employee, and Michael Smith will not voluntarily terminate his
employment with Basin, prior to February 28, 2001.
<PAGE>   163

                                                                         ANNEX B

October 28, 2000

Board of Directors
Basin Exploration, Inc.
1670 Broadway
Suite 2800
Denver, CO 80202

Gentlemen:

     You have requested our opinion as to the fairness from a financial point of
view to the holders of the outstanding shares of Common Stock, par value $.01
per share (the "Shares"), of Basin Exploration, Inc. (the "Company") of the
exchange ratio of .3974 shares of Common Stock, par value $.01 per share ("Stone
Common Stock"), of Stone Energy Corp. ("Stone") to be received for each Share
(the "Exchange Ratio") pursuant to the Agreement and Plan of Merger, dated as of
October 28, 2000, among Stone, Partner Acquisition Corp., a wholly-owned
subsidiary of Stone, and the Company (the "Agreement").

     Goldman, Sachs & Co., as part of its investment banking business, is
continually engaged in the valuation of businesses and their securities in
connection with mergers and acquisitions, negotiated underwritings, competitive
biddings, secondary distributions of listed and unlisted securities, private
placements and valuations for estate, corporate and other purposes. We are
familiar with the Company having acted as its financial advisor in connection
with, and having participated in certain of the negotiations leading to, the
Agreement. We are also familiar with the Company having provided certain
investment banking services to the Company from time to time, including acting
as managing underwriter of a public offering of 4,000,000 Shares in June 1999.
Peter K. Barker, an advisory director of Goldman Sachs, is a director of Stone.
Goldman, Sachs & Co. provides a full range of financial advisory and securities
services and, in the course of its normal trading activities, may from time to
time affect transactions and hold securities, including derivative securities,
of the Company or Stone for its own account and for the accounts of customers.

     In connection with this opinion, we have reviewed, among other things, the
Agreement; Annual Reports to Stockholders and Annual Reports on Form 10-K of the
Company and Stone for the five years ended December 31, 1999; certain interim
reports to stockholders and Quarterly Reports on Form 10-Q of the Company and
Stone; certain other communications from the Company and Stone to their
respective stockholders; and certain internal financial analyses and forecasts
for the Company and Stone prepared by their respective managements, including
certain cost savings and operating synergies projected by the management of the
Company to result from the transaction contemplated by the Agreement (the
"Synergies"). We also have held discussions with members of the senior
management of the Company regarding their assessment of the strategic rationale
for, and the potential benefits of, the transaction contemplated by the
Agreement and its past and current business operations, financial condition and
future prospects. In addition, we have reviewed the reported price and trading
activity for the Shares and the shares of Stone Common Stock, compared certain
financial and stock market information for the Company and Stone with similar
information for certain other companies the securities of which are publicly
traded, reviewed the financial terms of certain recent business combinations in
the upstream oil and gas industry specifically and in other industries generally
and performed such other studies and analyses as we considered appropriate.

     We have relied upon the accuracy and completeness of all of the financial
and other information discussed with or reviewed by us and have assumed such
accuracy and completeness for purposes of rendering this opinion. In that
regard, we have assumed with your consent that the internal financial forecasts
prepared by the management of the Company and Stone, including the Synergies,
have been
<PAGE>   164
Basin Exploration, Inc.
October 28, 2000
Page 2

reasonably prepared on a basis reflecting the best currently available estimates
and judgments of the Company and Stone. We also have assumed with your consent
that the transaction contemplated by the Agreement will be accounted for as a
pooling-of-interests under generally accepted accounting principles. In
addition, we have not made an independent evaluation or appraisal of the assets
and liabilities of the Company or Stone or any of their subsidiaries and we have
not been furnished with any such evaluation or appraisal. With respect to oil
and gas reserve information, we are not experts in the evaluation of oil and gas
properties and, with your consent, have relied without independent verification
solely upon the oil and gas reserve information and internal estimates prepared
by the management of the Company. Our advisory services and the opinion
expressed herein are provided for the information and assistance of the Board of
Directors of the Company in connection with its consideration of the transaction
contemplated by the Agreement and such opinion does not constitute a
recommendation as to how any holder of Shares should vote with respect to such
transaction.

     Based upon and subject to the foregoing and based upon such other matters
as we consider relevant, it is our opinion that as of the date hereof the
Exchange Ratio pursuant to the Agreement is fair from a financial point of view
to the holders of Shares.

                                            Very truly yours
<PAGE>   165

                                                                         ANNEX C

                           [MERRILL LYNCH LETTERHEAD]

                                                                October 28, 2000

Board of Directors
Stone Energy Corporation
625 East Kaliste Saloom Road
Lafayette, Louisiana 70508

Attn: James H. Stone
     Chairman and Chief Executive Officer

Members of the Board of Directors:

     You have informed us that Basin Exploration, Inc. (the "Company"), Stone
Energy Corporation (the "Acquiror") and Partner Acquisition Corp., a newly
formed, wholly owned subsidiary of the Acquiror (the "Acquisition Sub"), propose
to enter into an Agreement and Plan of Merger dated as of October 28, 2000 (the
"Agreement") pursuant to which the Company will be merged with the Acquisition
Sub in a transaction (the "Merger"). As a result of the Merger, each outstanding
share of the Company's common stock, par value $0.01 per share (the "Company
Shares"), will be converted into the right to receive 0.3974 shares (the
"Exchange Ratio") of the common stock of the Acquiror, par value $0.01 per share
(the "Acquiror Shares").

     You have asked us whether, in our opinion, the Exchange Ratio is fair from
a financial point of view to the Acquiror.

     In arriving at the opinion set forth below, we have, among other things:

          (1) Reviewed certain publicly available business and financial
     information relating to the Company and the Acquiror that we deemed to be
     relevant, including (a) Annual Reports on Form 10-K and related audited
     financial statements for the fiscal years for the three years ended
     December 31, 1999 and (b) the Quarterly Reports on Form 10-Q and related
     unaudited financial statements for the quarterly periods ending March 31,
     2000 and June 30, 2000.

          (2) Reviewed the reserve reports prepared as of December 31, 1999 by
     Atwater Consultants, Ltd. and Cawley, Gillespie & Associates, Inc., both
     independent petroleum engineers (collectively, the "Acquiror Reserve
     Reports").

          (3) Reviewed the reserve report of Ryder Scott Company Petroleum
     Engineers, independent petroleum engineers, for approximately 28% of the
     Company's proved reserve quantities in the Gulf of Mexico as of December
     31, 1999, the audit report by Ryder Scott Company Petroleum Engineers of
     the Company's estimates for the Company's remaining properties as of
     December 31, 1999, and the Company's estimates of the Company's remaining
     properties as of December 31, 1999 (collectively, the "Company Reserve
     Reports").

          (4)  Reviewed certain information, including production forecasts of
     existing hydrocarbon reserves, and financial forecasts (reviewed using
     identical commodity price assumptions), relating to the business, earnings,
     cash flow, assets, liabilities and prospects of the Company and the
     Acquiror, furnished to us by the Company and the Acquiror;
<PAGE>   166

          (5)  Conducted discussions with members of senior management of the
     Company and the Acquiror concerning the matters described in clauses 1 and
     4 above, as well as their respective businesses and prospects before and
     after giving effect to the Merger;

          (6)  Reviewed the market prices and valuation multiples for the
     Company Shares and the Acquiror Shares and compared them with those of
     certain publicly traded companies that we deemed to be relevant;

          (7)  Reviewed the results of operations of the Company and the
     Acquiror and compared them with those of certain publicly traded companies
     that we deemed to be relevant;

          (8)  Compared the proposed financial terms of the Merger with the
     financial terms of certain other transactions that we deemed to be
     relevant;

          (9)  Participated in certain discussions and negotiations among
     representatives of the Company and the Acquiror and their financial and
     legal advisors;

          (10) Reviewed the potential pro forma impact of the Merger;

          (11) Reviewed a draft of the Agreement dated October 26, 2000; and

          (12) Reviewed such other financial studies and analyses and took into
     account such other matters as we deemed necessary, including our assessment
     of general economic, market and monetary conditions.

     In preparing our opinion, we have assumed and relied on the accuracy and
completeness of all information supplied or otherwise made available to us,
discussed with or reviewed by or for us, or publicly available, and we have not
assumed any responsibility for independently verifying such information or
undertaken an independent evaluation or appraisal of any of the assets or
liabilities of the Company or the Acquiror or been furnished with any such
evaluation or appraisal. In addition, we have not conducted, or assumed any
obligation to conduct, any physical inspection of the properties or facilities
of the Company or the Acquiror. With respect to the production and financial
forecast information furnished to or discussed with us by the Company or the
Acquiror, we have assumed that they have been reasonably prepared and reflect
the best currently available estimates and judgment of the Company's or the
Acquiror's management as to the expected future financial performance of the
Company or the Acquiror, as the case may be, and their respective petroleum
engineers as to their respective reserves, their future hydrocarbon production
volumes and associated costs. We have further assumed that the Merger will be
accounted for as a pooling of interests under generally accepted accounting
principles and that it will qualify as a tax-free reorganization for U.S.
federal income tax purposes. We have also assumed that the final form of the
Agreement will be substantially similar to the last draft reviewed by us.

     Our opinion is necessarily based upon market, economic and other conditions
as they exist and can be evaluated on, and on the information made available to
us as of, the date hereof. We have assumed that in the course of obtaining the
necessary regulatory or other consents or approvals (contractual or otherwise)
for the Merger, no restrictions, including any divestiture requirements or
amendments or modifications, will be imposed that will have a material adverse
effect on the contemplated benefits of the Merger.

     We are acting as financial advisor to the Acquiror in connection with the
Merger and will receive a fee from the Acquiror for our services, a significant
portion of which is contingent upon the consummation of the Merger. In addition,
the Acquiror has agreed to indemnify us for certain liabilities arising out of
our engagement. We have, in the past, provided financial advisory and financing
services to the Acquiror and may continue to do so and have received, and may
receive, fees for the rendering of such services. In addition, in the ordinary
course of our business, we may actively trade the Company Shares, as well as the
Acquiror Shares and other securities of the Acquiror for our own account and for
the accounts of customers and, accordingly, may at any time hold a long or short
position in such securities.

     This opinion is for the use and benefit of the Board of Directors of the
Acquiror. Our opinion does not address the merits of the underlying decision by
the Acquiror to engage in the Merger and does not
<PAGE>   167

constitute a recommendation to any shareholder of the Acquiror as to how such
shareholder should vote on the proposed Merger or any matter related thereto.

     We are not expressing any opinion herein as to the prices at which the
Acquiror Shares will trade following the announcement or consummation of the
Merger.

     On the basis of and subject to the foregoing, we are of the opinion that,
as of the date hereof, the Exchange Ratio is fair from a financial point of view
to the Acquiror.

                                            Very truly yours,

                                            MERRILL LYNCH, PIERCE, FENNER &
                                            SMITH INCORPORATED
<PAGE>   168

                                                                         ANNEX D

                            CERTIFICATE OF AMENDMENT
                                     OF THE
                          CERTIFICATE OF INCORPORATION
                                       OF
                            STONE ENERGY CORPORATION

     Stone Energy Corporation (the "Company"), a corporation organized and
existing under and by virtue of the General Corporation Law of the State of
Delaware, does hereby certify, in accordance with Section 242 of the Delaware
General Corporation Law:

     FIRST:  That the Board of Directors of the Company duly adopted resolutions
setting forth a proposed amendment of the Certificate of Incorporation of the
Company, which Certificate of Incorporation was filed with the Secretary of
State of Delaware on March 15, 1993, as amended by a Certificate of Amendment
filed with the Secretary of State of Delaware on June 4, 1993, approving said
amendment, declaring it to be advisable and recommending said amendment to the
stockholders of the Company for approval thereof. The resolutions setting forth
the proposed amendment are as follows:

          RESOLVED, that this Board of Directors hereby determines that it is
     desirable and in the best interests of the Company and its stockholders to
     amend the Company's Certificate of Incorporation, as amended, to increase
     the number of shares of authorized Common Stock (the "Certificate
     Amendment");

          RESOLVED, that, pursuant to Section 242 of the Delaware General
     Corporation Law (the "DGCL"), and authority granted to and vested in the
     Board of Directors by the provisions of the Company's Certificate of
     Incorporation, as amended, the Board of Directors hereby approves the
     following proposed amendment to the Company's Certificate of Incorporation,
     as amended, and directs that such amendment be submitted to the
     stockholders of the Company for approval at the Special Meeting provided
     for in these resolutions in the form set forth below:

        "Resolved, that the first sentence of Article FOURTH of the Company's
        Certificate of Incorporation, as amended, be, and it hereby is, amended
        to read as follows:

        "FOURTH: The total number of shares of capital stock of the corporation
        shall be             , which shall consist of 5,000,000 shares of
        Preferred Stock, par value of $.01 per share, and             shares of
        Common Stock, par value of $.01 per share."

          RESOLVED, that, if the stockholders shall have voted for the
     Certificate Amendment, the Authorized Officers of the Company be, and each
     of them hereby is, authorized and directed, in the name and on behalf of
     the Company, to prepare, execute and file with the Secretary of State of
     the State of Delaware a certificate of amendment to the Certificate of
     Incorporation, as amended, in such form with such changes therein as the
     officers executing the same shall approve, the signature of such officers
     of the Company thereon to be conclusive evidence of the approval of such
     changes.

     SECOND:  That at a special meeting of stockholders held on           ,
2000, the foregoing amendment was duly approved by more than a majority of the
outstanding shares of Common Stock of the Company entitled to vote thereon, all
in accordance with Section 242 of the Delaware General Corporation Law.
<PAGE>   169

     IN WITNESS WHEREOF, the Company has caused this certificate to be signed by
D. Peter Canty, its Chief Operating Officer, and attested by Andrew L. Gates,
III, its Secretary, this      day of           , 2001.

                                            STONE ENERGY CORPORATION

                                            By:
                                              ----------------------------------
                                                D. Peter Canty
                                                Chief Operating Officer

ATTEST:

------------------------------------------------------
Andrew L. Gates, III
Secretary
<PAGE>   170


                            STONE ENERGY CORPORATION
                      PROXY SOLICITED BY BOARD OF DIRECTORS
                       FOR SPECIAL MEETING OF STOCKHOLDERS
                                     , 2000

     The undersigned stockholder of Stone Energy Corporation, a Delaware
corporation (the "Company"), hereby revokes all previous proxies with respect to
the matters set forth herein and appoints D. Peter Canty and Andrew L. Gates,
III, or either of them, attorneys, agents and proxies of the undersigned, with
full power of substitution to each of them, to vote all the shares of common
stock, par value $0.01 per share, of the Company which are entitled to one vote
per share and which the undersigned may be entitled to vote at the special
meeting of stockholders of the Company to be held at          , on            ,
2000, at       a.m., C.S.T., and at any adjournment of such meeting, with all
powers which the undersigned would possess if personally present:

     1.   To approve an amendment to Stone's certificate of incorporation to
          increase the authorized shares of Stone's common stock from 25,000,000
          shares to             shares;

     2.   To approve the issuance of shares of Stone common stock pursuant to
          the agreement and plan of merger, dated October 28, 2000, among the
          Company, Partner Acquisition Corp. and Basin Exploration, Inc.; and

     3.   To vote upon such other matters as may be properly brought before the
          meeting or any adjournment thereof.

     Approval of the proposal to amend Stone's certificate of incorporation is a
     prerequisite to approval of the proposal for the share issuance.

     If no directions are given, the individuals designated above will vote for
     the above proposals and, at their discretion, on any other matter that may
     come before the meeting.

     The undersigned acknowledges receipt of the Notice of Special Meeting of
     Stockholders and the Joint Proxy Statement/Prospectus.

          (CONTINUED AND TO BE VOTED, DATED AND SIGNED ON REVERSE SIDE)



<PAGE>   171


                            STONE ENERGY CORPORATION
                    COMMON STOCK PROXY ONE (1) VOTE PER SHARE
                          PLEASE MARK VOTES [-] OR [X]

THE BOARD OF DIRECTORS RECOMMENDS A VOTE FOR THE FOLLOWING PROPOSALS:

THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

     No. 1. To approve the amendment to Stone's certificate of incorporation to
increase the authorized shares of Stone's common stock from 25,000,000 shares of
common stock to             shares of common stock.

         [ ] FOR                 [ ] AGAINST             [ ] ABSTAIN

     No. 2. To approve the issuance of common stock of Stone pursuant to the
proposed merger transaction involving Stone and Basin Exploration, Inc.

         [ ] FOR                 [ ] AGAINST             [ ] ABSTAIN

    APPROVAL OF THE PROPOSAL TO AMEND STONE'S CERTIFICATE OF INCORPORATION IS
       A PREREQUISITE TO APPROVAL OF THE PROPOSAL FOR THE SHARE ISSUANCE

  PLEASE COMPLETE, SIGN AND PROMPTLY MAIL THIS PROXY IN THE ENCLOSED ENVELOPE.


Signature                                          Dated:
          -----------------------------------             ----------------------

NOTE: Stockholder(s) should sign above exactly as name(s) appears hereon. But
minor discrepancies in such signatures shall not invalidate their proxy. If more
than one stockholder, all should sign.

      Please date, sign and mail your proxy card back as soon as possible!

                              THANK YOU FOR VOTING.



<PAGE>   172


                             BASIN EXPLORATION, INC.
                      PROXY SOLICITED BY BOARD OF DIRECTORS
                       FOR SPECIAL MEETING OF STOCKHOLDERS
                                     , 2000

     The undersigned stockholder of Basin Exploration, Inc., a Delaware
corporation (the "Company"), hereby revokes all previous proxies with respect to
the matters set forth herein and appoints Michael S. Smith and Howard L. Boigon,
or either of them, attorneys, agents and proxies of the undersigned, with full
power of substitution to each of them, to vote all the shares of common stock,
par value $0.01 per share, of the Company which are entitled to one vote per
share and which the undersigned may be entitled to vote at the special meeting
of stockholders of the Company to be held at             , on              ,
2000, at      a.m., M.S.T., and at any adjournment of such meeting, with all
powers which the undersigned would possess if personally present:

     1.   To approve the merger agreement dated as of October 28, 2000, among
          Stone Energy Corporation, Partner Acquisition Corp., which is a
          newly-formed subsidiary of Stone Energy Corporation, and Basin
          Exploration, Inc., and the transactions contemplated by the merger
          agreement, including the merger; and

     2.   To vote upon such other matters as may be properly brought before the
          meeting or any adjournment thereof.

     If no directions are given, the individuals designated above will vote for
     the above proposals and, at their discretion, on any other matter that may
     come before the meeting.

     The undersigned acknowledges receipt of the Notice of Special Meeting of
     Stockholders and the Joint Proxy Statement/Prospectus.

          (CONTINUED AND TO BE VOTED, DATED AND SIGNED ON REVERSE SIDE)
--------------------------------------------------------------------------------



<PAGE>   173


                             BASIN EXPLORATION, INC.
                    COMMON STOCK PROXY ONE (1) VOTE PER SHARE
                          PLEASE MARK VOTES [-] OR [X]

THE BOARD OF DIRECTORS RECOMMENDS A VOTE FOR THE FOLLOWING PROPOSAL:

THIS PROXY IS SOLICITED ON BEHALF OF THE BOARD OF DIRECTORS

     No. 1. To approve the Agreement and Plan of Merger, dated as of October 28,
2000, among Stone Energy Corporation, Partner Acquisition Corp., a wholly-owned
subsidiary of Stone, and Basin, and the transactions contemplated thereby,
including the merger, pursuant to which Partner Acquisition Corp. will be merged
with and into Basin and each share of common stock, $0.01 par value per share,
of Basin issued and outstanding immediately prior to the merger (other than
shares held by Stone, Basin or their respective subsidiaries, which will be
canceled) will be converted into the right to receive .3974 of a share of common
stock, $0.01 par value, of Stone.

         [ ] FOR                 [ ] AGAINST             [ ] ABSTAIN

     All other matters that may come before the meeting.

      [TELEPHONE PICTURE] VOTE BY TELEPHONE OR INTERNET [COMPUTER PICTURE]
                          QUICK *** EASY *** IMMEDIATE

YOUR VOTE IS IMPORTANT!--YOU CAN VOTE IN ONE OF THREE WAYS:

1.   TO VOTE BY PHONE: Call toll-free 1-800-840-1208 on a touch tone telephone
     24 HOURS A DAY-7 DAYS A WEEK

    There is NO CHARGE to you for this call.--HAVE YOUR PROXY CARD IN HAND.
        You will be asked to enter a Control Number, which is located in
              the box on the lower right hand corner of this form

     To vote as the board of directors of Basin recommends on the proposal,
     press 1; AGAINST, press 9; ABSTAIN, press 0.

                    WHEN ASKED, PLEASE CONFIRM BY PRESSING 1.

                                       OR

2.   TO VOTE BY INTERNET: Follow the instructions at our Website Address:
     http://www.eproxy.com/

                                       OR

3.   TO VOTE BY PROXY CARD: Mark, sign and date your proxy card and return
     promptly in the enclosed envelope.

NOTE: IF YOU VOTE BY INTERNET OR TELEPHONE, THERE IS NO NEED TO MAIL BACK YOUR
PROXY CARD; IF YOU DO NOT VOTE BY INTERNET OR TELEPHONE, PLEASE COMPLETE, SIGN
AND PROMPTLY MAIL THIS PROXY IN THE ENCLOSED ENVELOPE.

Signature                                             Dated:
          ----------------------------------------           ------------------

NOTE: Stockholder(s) should sign above exactly as name(s) appears hereon. But
minor discrepancies in such signatures shall not invalidate their proxy. If more
than one stockholder, all should sign.

      Please date, sign and mail your proxy card back as soon as possible!

                              THANK YOU FOR VOTING


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