UNION PACIFIC RESOURCES GROUP INC
8-K, 2000-04-07
CRUDE PETROLEUM & NATURAL GAS
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<PAGE>   1
                             Washington, D.C. 20549

                                    FORM 8-K

                                 CURRENT REPORT

                     Pursuant to Section 13 or 15(d) of the
                         Securities Exchange Act of 1934


         Date of Report (Date of earliest event reported) April 2, 2000

                       UNION PACIFIC RESOURCES GROUP INC.
- --------------------------------------------------------------------------------
               (Exact name of registrant as specified in charter)



     Utah                          1-13916                       13-2647483
- --------------------------------------------------------------------------------
(State or other                  (Commission                  (IRS Employer
jurisdiction of                  File Number)               Identification No.)
incorporation)

  777 Main Street, Fort Worth, Texas                               76102
- --------------------------------------------------------------------------------
(Address of principal executive offices)                         (Zip Code)

Registrant's telephone number including area code             817-321-6000




<PAGE>   2



Item 5.  Other Events.

         Union Pacific Resources Group Inc. ("UPR"), Anadarko Petroleum
Corporation, a Delaware Corporation ("Anadarko"), and Dakota Merger Corp., a
Utah corporation and wholly owned subsidiary of Anadarko ("Subcorp"), entered
into an Agreement and Plan of Merger, dated as of April 2, 2000 (the "Merger
Agreement"), pursuant to which Subcorp will merge with and into UPR, and UPR
will become a wholly owned subsidiary of Anadarko.

         In connection with the execution of the Merger Agreement, UPR and
Anadarko entered into a Stock Option Agreement, dated as of April 2, 2000 (the
"UPR Stock Option Agreement"), pursuant to which UPR granted Anadarko an option,
exercisable under certain circumstances specified in the UPR Stock Option
Agreement, to purchase up to 50,138,515 shares of common stock, no par value, of
UPR ("UPR Common Stock") (approximately 19.9% of the outstanding shares of UPR
Common Stock, without giving effect to the exercise of the option) at the
purchase price stated therein.

         In connection with the execution of the Merger Agreement, Anadarko and
UPR entered into a Stock Option Agreement, dated as of April 2, 2000 (the
"Anadarko Stock Option Agreement"), pursuant to which Anadarko granted UPR an
option, exercisable under certain circumstances specified in the Anadarko Stock
Option Agreement, to purchase up to 25,886,726 shares of common stock, par value
$0.10 per share, of Anadarko ("Anadarko Common Stock") (approximately 19.9% of
the outstanding Anadarko Common Stock, without giving effect to the exercise of
the option) at the purchase price stated therein.

         In connection with the Merger Agreement, UPR and Harris Trust and
Savings Bank, as Rights Agent (the "Rights Agent"), entered into Amendment No.
1, dated as of April 2, 2000 (the "Rights Agreement Amendment"), to the Amended
and Restated Rights Agreement, dated as of December 1, 1998, between UPR and the
Rights Agent (the "Rights Agreement"), providing that Anadarko is exempt from
the definition of "Acquiring Person" contained in the Rights Agreement and that
no "Shares Acquisition Date" or "Distribution Date" will occur as a result of
the execution of the merger agreement, the execution of the UPR Stock Option
Agreement, or the acquisition, or the transfer of UPR Common Stock by UPR
pursuant to the UPR Stock Option Agreement.

         Holders of UPR Common Stock will receive a proxy statement/prospectus
describing the background and terms of the merger and seeking approval of the
merger. It is presently anticipated that a meeting of UPR shareholders will be
held to approve the merger in July of 2000, although the actual date may be
earlier or later. In light of the pending transaction, the UPR Board of
Directors has determined to postpone indefinitely the 2000 Annual Meeting of
Shareholders of UPR.

         The Merger Agreement, the UPR Stock Option Agreement, the Anadarko
Stock Option Agreement, and the Rights Agreement Amendment are attached hereto
as exhibits and are incorporated herein by reference. The foregoing descriptions
of the Merger Agreement, the UPR Stock Option Agreement, the Anadarko Stock
Option Agreement, and the Rights Agreement Amendment are qualified in their
entirety by reference to Exhibits 2.1, 2.2, 2.3, and 2.4, respectively, hereof.

<PAGE>   3

Item 7(c).  Exhibits.

2.1      Agreement and Plan of Merger, dated as of April 2, 2000, among
         Anadarko, Subcorp and UPR.

2.2      Stock Option Agreement, dated as of April 2, 2000, between UPR and
         Anadarko.

2.3      Stock Option Agreement, dated as of April 2, 2000, between Anadarko and
         UPR.

2.4      Amendment No. 1 to Rights Agreement, dated as of April 2, 2000, between
         UPR and Rights Agent.

                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934,
Registrant has duly caused this report to be signed on its behalf by the
undersigned hereunto duly authorized.

                               UNION PACIFIC RESOURCES GROUP INC.

                               /s/ KERRY R. BRITTAIN
                               -------------------------------------------------
                               By: Kerry R. Brittain
                                   Vice President, General Counsel and Secretary


<PAGE>   4


                               INDEX TO EXHIBITS


<TABLE>
<CAPTION>

 EXHIBIT NO.   DESCRIPTION
 -----------   -----------


<S>            <C>

     2.1       Agreement and Plan of Merger, dated as of April 2, 2000, among
               Anadarko, Subcorp and UPR.

     2.2       Stock Option Agreement, dated as of April 2, 2000, between UPR
               and Anadarko.

     2.3       Stock Option Agreement, dated as of April 2, 2000, between
               Anadarko and UPR.

     2.4       Amendment No. 1 to Rights Agreement, dated as of April 2, 2000,
               between UPR and Rights Agent.
</TABLE>

<PAGE>   1
                                                                     EXHIBIT 2.1

                                                                  CONFORMED COPY




                          AGREEMENT AND PLAN OF MERGER

                                      AMONG

                         ANADARKO PETROLEUM CORPORATION
                                  ("Anadarko"),

                               DAKOTA MERGER CORP.
                  a wholly owned direct subsidiary of Anadarko
                                  ("Subcorp"),



                                       and



                       UNION PACIFIC RESOURCES GROUP INC.
                                     ("UPR")










                                  April 2, 2000



<PAGE>   2

                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                                              PAGE
<S>                                                                                                          <C>
PRELIMINARY STATEMENTS.........................................................................................1
AGREEMENT            ..........................................................................................1
ARTICLE I.           THE MERGER................................................................................1
         1.1      The Merger...................................................................................1
         1.2      Effective Time...............................................................................2
         1.3      Effects of the Merger........................................................................2
         1.4      Articles of Incorporation and By-laws........................................................2
         1.5      Directors and Officers of the Surviving Corporation..........................................2
         1.6      Additional Actions...........................................................................2
ARTICLE II.          CONVERSION OF SECURITIES..................................................................3
         2.1      Conversion of Capital Stock..................................................................3
         2.2      Exchange Ratio; Fractional Shares; Adjustments...............................................3
         2.3      Exchange of Certificates.....................................................................4
                      (a)      Exchange Agent..................................................................4
                      (b)      Exchange Procedures.............................................................4
                      (c)      Distributions with Respect to Unexchanged Shares................................5
                      (d)      No Further Ownership Rights in UPR Common Stock.................................5
                      (e)      Termination of Exchange Fund....................................................5
                      (f)      No Liability....................................................................6
                      (g)      Investment of Exchange Fund.....................................................6
                      (h)      Withholding Rights..............................................................6
         2.4      Treatment of Stock Options...................................................................6
ARTICLE III.         REPRESENTATIONS AND WARRANTIES OF ANADARKO AND
                     SUBCORP...................................................................................7
         3.1      Organization and Standing....................................................................7
         3.2      Subsidiaries and Investments.................................................................8
         3.3      Corporate Power and Authority................................................................8
         3.4      Capitalization of Anadarko and Subcorp.......................................................8
         3.5      Conflicts; Consents and Approval.............................................................9
         3.6      Brokerage and Finder's Fees.................................................................10
         3.7      Reorganization..............................................................................10
         3.8      No Material Adverse Change..................................................................10
         3.9      Anadarko SEC Documents......................................................................10
         3.10     Taxes.......................................................................................11
         3.11     Compliance with Law.........................................................................13
         3.12     Registration Statement; Joint Proxy Statement...............................................13
         3.13     Litigation..................................................................................13
         3.14     Anadarko Employee Benefit Plans.............................................................14
         3.15     Contracts...................................................................................17
         3.16     Labor Matters...............................................................................18
         3.17     Undisclosed Liabilities.....................................................................18
         3.18     Permits; Compliance.........................................................................18
</TABLE>

                                      -i-

<PAGE>   3


<TABLE>
<S>                                                                                                       <C>
         3.19     Environmental Matters.......................................................................18
         3.20     Opinion of Financial Advisor................................................................19
         3.21     Board Recommendation; Required Vote.........................................................19
         3.22     State Takeover Laws; Rights Agreement.......................................................19
ARTICLE IV.          REPRESENTATIONS AND WARRANTIES OF UPR....................................................20
         4.1      Organization and Standing...................................................................20
         4.2      Subsidiaries and Investments................................................................20
         4.3      Corporate Power and Authority...............................................................21
         4.4      Capitalization of UPR.......................................................................21
         4.5      Conflicts; Consents and Approvals...........................................................22
         4.6      Brokerage and Finder's Fees.................................................................22
         4.7      Reorganization..............................................................................22
         4.8      No Material Adverse Change..................................................................22
         4.9      UPR SEC Documents...........................................................................23
         4.10     Taxes.......................................................................................23
         4.11     Compliance with Law.........................................................................25
         4.12     Registration Statement; Joint Proxy Statement...............................................25
         4.13     Litigation..................................................................................25
         4.14     UPR Employee Benefit Plans..................................................................25
         4.15     Contracts...................................................................................29
         4.16     Labor Matters...............................................................................29
         4.17     Undisclosed Liabilities.....................................................................29
         4.18     Permits; Compliance.........................................................................29
         4.19     Environmental Matters.......................................................................30
         4.20     Opinion of Financial Advisor................................................................30
         4.21     Board Recommendation; Required Vote.........................................................30
         4.22     State Takeover Laws; Rights Agreement.......................................................30
ARTICLE V.           COVENANTS OF THE PARTIES.................................................................31
         5.1      Mutual Covenants............................................................................31
                      (a)      HSR Act Filings; Reasonable Efforts; Notification..............................31
                      (b)      Tax-Free Treatment.............................................................33
                      (c)      Public Announcements...........................................................33
                      (d)      Farmouts.......................................................................33
         5.2      Covenants of Anadarko.......................................................................33
                      (a)      Anadarko Stockholders Meeting..................................................33
                      (b)      Preparation of Registration Statement..........................................33
                      (c)      Conduct of Anadarko's Operations...............................................34
                      (d)      No Solicitation................................................................37
                      (e)      Indemnification; Directors' and Officers' Insurance............................38
                      (f)      NYSE Listing...................................................................39
                      (g)      Access.........................................................................39
                      (h)      Board of Directors of Anadarko.................................................39
                      (i)      Subsequent Financial Statements................................................39
                      (j)      Employees and Employee Benefits................................................39
         5.3      Covenants of UPR............................................................................40
                      (a)      UPR Stockholders Meeting.......................................................40
</TABLE>


                                      -ii-

<PAGE>   4


<TABLE>
<S>                                                                                                         <C>
                      (b)      Information for the Registration Statement and Preparation of
                                 Joint Proxy Statement........................................................41
                      (c)      Conduct of UPR's Operations....................................................41
                      (d)      No Solicitation................................................................44
                      (e)      Affiliates of UPR..............................................................45
                      (f)      Access.........................................................................45
                      (g)      Subsequent Financial Statements................................................46
ARTICLE VI.          CONDITIONS...............................................................................46
         6.1      Conditions to the Obligations of Each Party.................................................46
         6.2      Conditions to Obligations of UPR............................................................47
         6.3      Conditions to Obligations of Anadarko and Subcorp...........................................47
ARTICLE VII.         TERMINATION AND AMENDMENT................................................................48
         7.1      Termination by Mutual Consent...............................................................48
         7.2      Termination by UPR or Anadarko..............................................................48
         7.3      Termination by Anadarko.....................................................................49
         7.4      Termination by UPR..........................................................................49
         7.5      Effect of Termination.......................................................................50
         7.6      Amendment...................................................................................51
         7.7      Extension; Waiver...........................................................................51
ARTICLE VIII.        MISCELLANEOUS............................................................................52
         8.1      Survival of Representations and Warranties..................................................52
         8.2      Notices.....................................................................................52
         8.3      Interpretation..............................................................................53
         8.4      Counterparts................................................................................53
         8.5      Entire Agreement............................................................................53
         8.6      Third-Party Beneficiaries...................................................................54
         8.7      Governing Law...............................................................................54
         8.8      Consent to Jurisdiction; Venue..............................................................54
         8.9      Specific Performance........................................................................54
         8.10     Assignment..................................................................................54
         8.11     Expenses....................................................................................54
</TABLE>


                                     -iii-

<PAGE>   5


                          AGREEMENT AND PLAN OF MERGER

                  This Agreement and Plan of Merger (this "Agreement") is made
and entered into as of the 2nd day of April, 2000, by and among Anadarko
Petroleum Corporation, a Delaware corporation ("Anadarko"), Dakota Merger Corp.,
a Utah corporation and a wholly owned subsidiary of Anadarko ("Subcorp"), and
Union Pacific Resources Group Inc., a Utah corporation ("UPR").


                             PRELIMINARY STATEMENTS

                  A. The Board of Directors of Anadarko has determined that the
merger of Subcorp with and into UPR, with UPR as the surviving corporation (the
"Merger"), pursuant to which each share of UPR Common Stock (as defined in
Section 4.4) outstanding at the Effective Time (as defined in Section 1.2) will
be converted into the right to receive Anadarko Common Shares (as defined in
Section 3.4(a)) as more fully provided herein, is consistent with and in
furtherance of the long-term business strategy of Anadarko and Anadarko desires
to combine its businesses with the businesses operated by UPR.

                  B. The Board of Directors of UPR has determined that the
Merger is consistent with and in furtherance of the long-term business strategy
of UPR and UPR desires to combine its businesses with the businesses operated by
Anadarko and for the holders of shares of UPR Common Stock ("UPR Stockholders")
to have a continuing equity interest in the combined Anadarko/UPR businesses
through the ownership of Anadarko Common Shares.

                  C. The parties intend that the Merger constitute a tax-free
"reorganization" within the meaning of Section 368(a)(1)(A) of the Internal
Revenue Code of 1986, as amended (the "Code").

                  D. The respective Boards of Directors of Anadarko, Subcorp and
UPR have determined the Merger in the manner contemplated herein to be desirable
and in the best interests of their respective shareholders, and, by resolutions
duly adopted, have approved and adopted this Agreement.


                                    AGREEMENT

                  Now, therefore, in consideration of these premises and the
mutual and dependent promises hereinafter set forth, the parties hereto agree as
follows:

                                   ARTICLE I.

                                   THE MERGER

                  1.1 The Merger. Upon the terms and subject to the conditions
hereof, and in accordance with the provisions of the Utah Revised Business
Corporation Act (the "UBCA"), Subcorp shall be merged with and into UPR at the
Effective Time. As a result of the Merger, the separate corporate existence of
Subcorp shall cease and UPR shall continue its existence under

<PAGE>   6


the laws of the State of Utah. UPR, in its capacity as the corporation surviving
the Merger, is hereinafter sometimes referred to as the "Surviving Corporation."

                  1.2 Effective Time. As promptly as possible on the Closing
Date (as defined below), the parties hereto shall cause the Merger to be
consummated by filing with the Division of Corporations and Commercial Code of
the State of Utah (the "Utah Division") articles of merger (the "Articles of
Merger") in such form as is required by and executed in accordance with Section
16-10a-1105 of the UBCA. The Merger shall become effective (the "Effective
Time") when the Articles of Merger have been filed with the Utah Division or at
such later time as shall be agreed upon by Anadarko and UPR and specified in the
Articles of Merger. Prior to the filing referred to in this Section 1.2, a
closing (the "Closing") shall be held at the principal business offices of
Anadarko, or such other place as the parties hereto may agree as soon as
practicable (but in any event within three business days) following the date
upon which all conditions set forth in Article VI have been satisfied or waived,
or at such other date as Anadarko and UPR may agree; provided, that the
conditions set forth in Article VI have been satisfied or waived at or prior to
such date. The date on which the Closing takes place is referred to herein as
the "Closing Date."

                  1.3 Effects of the Merger. From and after the Effective Time,
the Merger shall have the effects set forth in Section 16-10a-1106 of the UBCA.

                  1.4 Articles of Incorporation and By-laws. The Articles of
Merger shall provide that at the Effective Time (i) the Articles of
Incorporation of the Surviving Corporation as in effect immediately prior to the
Effective Time shall be amended as of the Effective Time so as to contain the
provisions, and only the provisions, contained immediately prior thereto in the
Articles of Incorporation of Subcorp, except for Article I thereof, which shall
continue to read "The name of the corporation is `UNION PACIFIC RESOURCES GROUP
INC.'", and (ii) the By-laws of Subcorp in effect immediately prior to the
Effective Time shall be the By-laws of the Surviving Corporation; in each case,
until amended in accordance with the UBCA.

                  1.5 Directors and Officers of the Surviving Corporation. From
and after the Effective Time, the officers of UPR shall be the officers of the
Surviving Corporation and the directors of Subcorp shall be the directors of the
Surviving Corporation, in each case, until their respective successors are duly
elected and qualified. On or prior to the Closing Date, UPR shall deliver to
Anadarko evidence satisfactory to Anadarko of the resignations of the directors
of UPR, such resignations to be effective as of the Effective Time.

                  1.6 Additional Actions. If, at any time after the Effective
Time, the Surviving Corporation shall consider or be advised that any further
deeds, assignments or assurances in law or any other acts are necessary or
desirable to (a) vest, perfect or confirm, of record or otherwise, in the
Surviving Corporation its right, title or interest in, to or under any of the
rights, properties or assets of UPR, or (b) otherwise carry out the provisions
of this Agreement, UPR and its officers and directors shall be deemed to have
granted to the Surviving Corporation an irrevocable power of attorney to execute
and deliver all such deeds, assignments or assurances in law and to take all
acts necessary, proper or desirable to vest, perfect or confirm title to and
possession of such rights, properties or assets in the Surviving Corporation and
otherwise to


                                      -2-
<PAGE>   7

carry out the provisions of this Agreement, and the officers and directors of
the Surviving Corporation are authorized in the name of UPR or otherwise to take
any and all such action.

                                   ARTICLE II.

                            CONVERSION OF SECURITIES

                  2.1 Conversion of Capital Stock. At the Effective Time, by
virtue of the Merger and without any action on the part of Anadarko, Subcorp or
UPR or their respective shareholders:

                  (a) Each share of common stock of Subcorp ("Subcorp Common
Stock") issued and outstanding immediately prior to the Effective Time shall be
converted into one share of common stock of the Surviving Corporation. Such
newly issued shares shall thereafter constitute all of the issued and
outstanding capital stock of the Surviving Corporation.

                  (b) Subject to the other provisions of this Article II, each
share of UPR Common Stock issued and outstanding immediately prior to the
Effective Time shall be converted into and represent a number of Anadarko Common
Shares equal to the Exchange Ratio.

                  (c) Each share of capital stock of UPR held by UPR shall be
cancelled and retired and no payment shall be made in respect thereof.

                  2.2 Exchange Ratio; Fractional Shares; Adjustments.

                  (a) The "Exchange Ratio" shall be equal to 0.4550.

                  (b) No certificates for fractional Anadarko Common Shares
shall be issued as a result of the conversion provided for in Section 2.1(b) and
such fractional share interests will not entitle the owner thereof to vote or
have any rights of an Anadarko Stockholder (as defined in Section 3.3) or a
holder of Anadarko Common Shares.

                  (c) In lieu of any such fractional Anadarko Common Shares, the
holder of a certificate previously evidencing UPR Common Stock, upon
presentation of such fractional interest represented by an appropriate
certificate for UPR Common Stock to the Exchange Agent (as defined in Section
2.3(a)) pursuant to Section 2.3, shall be entitled to receive a cash payment
therefor in an amount equal to the value (determined with reference to the
closing price of Anadarko Common Shares as reported on the New York Stock
Exchange ("NYSE") Composite Tape ("NYSE Composite Tape") on the last full
trading day immediately prior to the Closing Date) of such fractional interest.
Such payment with respect to fractional shares is merely intended to provide a
mechanical rounding off of, and is not a separately bargained for,
consideration. If more than one certificate representing shares of UPR Common
Stock shall be surrendered for the account of the same holder, the number of
Anadarko Common Shares for which certificates have been surrendered shall be
computed on the basis of the aggregate number of shares represented by the
certificates so surrendered.




                                      -3-
<PAGE>   8

                  (d) In the event that, prior to the Effective Time, Anadarko
shall declare a stock dividend or other distribution payable in Anadarko Common
Shares or securities convertible into Anadarko Common Shares, or effect a stock
split, reclassification, combination or other change with respect to Anadarko
Common Shares, the Exchange Ratio set forth in this Section 2.2 shall be
adjusted to reflect such dividend, distribution, stock split, reclassification,
combination or other change.

                  2.3 Exchange of Certificates.

                  (a) Exchange Agent. Promptly following the Effective Time,
Anadarko shall deposit with ChaseMellon Shareholder Services, L.L.C. or such
other exchange agent as may be designated by Anadarko (the "Exchange Agent"),
for the benefit of UPR Stockholders, for exchange in accordance with this
Section 2.3, certificates representing Anadarko Common Shares issuable pursuant
to Section 2.1 in exchange for outstanding shares of UPR Common Stock and shall
from time-to-time deposit cash in an amount reasonably expected to be paid
pursuant to Section 2.2 (such Anadarko Common Shares and cash, together with any
dividends or distributions with respect thereto, the "Exchange Fund").

                  (b) Exchange Procedures. As soon as practicable after the
Effective Time, the Exchange Agent shall mail to each holder of record of a
certificate or certificates (the "Certificates") that immediately prior to the
Effective Time represented outstanding shares of UPR Common Stock whose shares
were converted into the right to receive Anadarko Common Shares pursuant to
Section 2.1(b), (i) a letter of transmittal (which shall specify that delivery
shall be effected, and risk of loss and title to the Certificates shall pass,
only upon delivery of the Certificates to the Exchange Agent, and shall be in
such form and have such other customary provisions as Anadarko may reasonably
specify) and (ii) instructions for effecting the surrender of the Certificates
in exchange for certificates representing Anadarko Common Shares. Upon surrender
of a Certificate for cancellation to the Exchange Agent, together with a duly
executed letter of transmittal, the holder of such Certificate shall be entitled
to receive in exchange therefor (i) a certificate or certificates representing
that whole number of Anadarko Common Shares which such holder has the right to
receive pursuant to Section 2.1 in such denominations and registered in such
names as such holder may request and (ii) a check representing the amount of
cash in lieu of fractional shares, if any, and unpaid dividends and
distributions, if any, which such holder has the right to receive pursuant to
the provisions of this Article II, after giving effect to any required
withholding tax. The shares represented by the Certificate so surrendered shall
forthwith be cancelled. No interest will be paid or accrued on the cash in lieu
of fractional shares, if any, and unpaid dividends and distributions, if any,
payable to holders of shares of UPR Common Stock. In the event of a transfer of
ownership of shares of UPR Common Stock that is not registered on the transfer
records of UPR, a certificate representing the proper number of Anadarko Common
Shares, together with a check for the cash to be paid in lieu of fractional
shares, if any, and unpaid dividends and distributions, if any, may be issued to
such transferee if the Certificate representing such shares of UPR Common Stock
held by such transferee is presented to the Exchange Agent, accompanied by all
documents required to evidence and effect such transfer and to evidence that any
applicable stock transfer taxes have been paid. Until surrendered as
contemplated by this Section 2.3, each Certificate shall be deemed at any time
after the Effective Time to represent only the right to receive upon surrender a
certificate representing Anadarko Common Shares and cash in lieu of fractional
shares, if any, and unpaid



                                      -4-
<PAGE>   9

dividends and distributions, if any, as provided in this Article II. If any
Certificate shall have been lost, stolen or destroyed, upon the making of an
affidavit of that fact by the person claiming such Certificate to be lost,
stolen or destroyed and, if required by Anadarko, the posting by such person of
a bond in such reasonable amount as Anadarko may direct as indemnity against any
claim that may be made against it with respect to such Certificate, the Exchange
Agent will deliver in exchange for such lost, stolen or destroyed Certificate, a
certificate representing the proper number of Anadarko Common Shares, together
with a check for the cash to be paid in lieu of fractional shares, if any, with
respect to the shares of UPR Common Stock formerly represented thereby, and
unpaid dividends and distributions on Anadarko Common Shares, if any, as
provided in this Article II.

                  (c) Distributions with Respect to Unexchanged Shares.
Notwithstanding any other provisions of this Agreement, no dividends or other
distributions declared or made after the Effective Time with respect to Anadarko
Common Shares having a record date after the Effective Time shall be paid to the
holder of any unsurrendered Certificate, and no cash payment in lieu of
fractional shares shall be paid to any such holder, until the holder shall
surrender such Certificate as provided in this Section 2.3. Subject to the
effect of Applicable Laws (as defined in Section 3.11), following surrender of
any such Certificate, there shall be paid to the holder of the certificates
representing whole Anadarko Common Shares issued in exchange therefor, without
interest, (i) at the time of such surrender, the amount of dividends or other
distributions with a record date after the Effective Time theretofore payable
with respect to such whole Anadarko Common Shares and not paid, less the amount
of any withholding taxes that may be required thereon, and (ii) at the
appropriate payment date subsequent to surrender, 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 Anadarko Common Shares, less the amount of any withholding taxes
which may be required thereon.

                  (d) No Further Ownership Rights in UPR Common Stock. All
Anadarko Common Shares issued upon surrender of Certificates in accordance with
the terms hereof (including any cash paid pursuant to this Article II) shall be
deemed to have been issued in full satisfaction of all rights pertaining to such
shares of UPR Common Stock represented thereby, and, as of the Effective Time,
the stock transfer books of UPR shall be closed and there shall be no further
registration of transfers on the stock transfer books of UPR of shares of UPR
Common Stock outstanding immediately prior to the Effective Time. If, after the
Effective Time, Certificates are presented to the Surviving Corporation for any
reason, they shall be cancelled and exchanged as provided in this Section 2.3.
Certificates surrendered for exchange by any person constituting an "affiliate"
of UPR for purposes of Rule 145(c) under the Securities Act of 1933, as amended
(together with the rules and regulations thereunder, the "Securities Act"),
shall not be exchanged until Anadarko has received written undertakings from
such person in the form attached as Exhibit A to this Agreement.

                  (e) Termination of Exchange Fund. Any portion of the Exchange
Fund that remains undistributed to UPR Stockholders six months after the date of
the mailing required by Section 2.3(b) shall be delivered to Anadarko, upon
demand thereby, and holders of Certificates previously representing shares of
UPR Common Stock who have not theretofore complied with this Section 2.3 shall
thereafter look only to Anadarko for payment of any claim to Anadarko



                                      -5-
<PAGE>   10

Common Shares, cash in lieu of fractional shares thereof, or dividends or
distributions, if any, in respect thereof.

                  (f) No Liability. None of Anadarko, the Surviving Corporation
or the Exchange Agent shall be liable to any person in respect of any shares of
UPR Common Stock (or dividends or distributions with respect thereto) or cash
from the Exchange Fund delivered to a public official pursuant to any applicable
abandoned property, escheat or similar law. If any Certificates shall not have
been surrendered prior to seven years after the Effective Time (or immediately
prior to such earlier date on which any cash, any cash in lieu of fractional
shares or any dividends or distributions with respect to whole shares of UPR
Common Stock in respect of such Certificate would otherwise escheat to or become
the property of any Governmental Authority (as defined in Section 3.4(d)), any
such cash, dividends or distributions in respect of such Certificate shall, to
the extent permitted by Applicable Laws, become the property of Anadarko, free
and clear of all claims or interest of any person previously entitled thereto.

                  (g) Investment of Exchange Fund. The Exchange Agent shall
invest any cash included in the Exchange Fund, as directed by Anadarko, on a
daily basis. Any interest and other income resulting from such investments shall
be paid to Anadarko upon termination of the Exchange Fund pursuant to Section
2.3(e).

                  (h) Withholding Rights. Each of the Surviving Corporation and
Anadarko shall be entitled to deduct and withhold from the consideration
otherwise payable pursuant to this Agreement to any holder of shares of UPR
Common Stock such amounts as it is required to deduct and withhold with respect
to the making of such payment under the 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
Anadarko, 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
UPR Common Stock in respect of which such deduction and withholding was made by
the Surviving Corporation or Anadarko, as the case may be.

                  2.4 Treatment of Stock Options.

                  (a) Prior to the Effective Time, Anadarko and UPR shall take
all such actions as may be necessary to cause each unexpired and unexercised
outstanding option granted or issued under stock option plans of UPR in effect
on the date hereof (each, a "UPR Option") to be automatically converted at the
Effective Time into an option (a "Anadarko Exchange Option") to purchase that
number of Anadarko Common Shares equal to the number of shares of UPR Common
Stock subject to the UPR Option immediately prior to the Effective Time (without
regard to any actual restrictions on exerciseability) multiplied by the Exchange
Ratio (and rounded to the nearest share), with an exercise price per share equal
to the exercise price per share that existed under the corresponding UPR Option
divided by the Exchange Ratio (and rounded to the nearest cent), and with other
terms and conditions that are the same as the terms and conditions of such UPR
Option immediately before the Effective Time provided, that Anadarko shall
equitably adjust the applicable performance target under any UPR Option that
contains performance targets; provided further that, with respect to any UPR
Option that is an "incentive stock option" within the meaning of Section 422 of
the Code, the foregoing



                                      -6-
<PAGE>   11

conversion shall be carried out in a manner satisfying the requirements of
Section 424(a) of the Code.

                  (b) In connection with the issuance of Anadarko Exchange
Options, Anadarko shall (i) reserve for issuance the number of Anadarko Common
Shares that will become subject to Anadarko Exchange Options pursuant to this
Section 2.4 and (ii) from and after the Effective Time, upon exercise of
Anadarko Exchange Options, make available for issuance all Anadarko Common
Shares covered thereby, subject to the terms and conditions applicable thereto.

                  (c) Anadarko agrees to use its reasonable efforts to file with
the Securities and Exchange Commission (the "Commission") within 30 days after
the Closing Date a registration statement on Form S-8 or other appropriate form
under the Securities Act to register Anadarko Common Shares issuable upon
exercise of the Anadarko Exchange Options and to use its reasonable efforts to
cause such registration statement to remain effective until the exercise or
expiration of such options and rights. Prior to the Effective Time, the Board of
Directors of Anadarko, or an appropriate committee of non-employee directors
thereof, shall adopt a resolution consistent with the interpretive guidance of
the Commission so that the acquisition by any officer or director of Anadarko
who may become a covered person of UPR for purposes of Section 16 of the
Securities Exchange Act of 1934, as amended (together with the rules and
regulations thereunder, the "Exchange Act") and the rules and regulations
thereunder ("Section 16") of Anadarko Common Shares or options to acquire
Anadarko Common Shares pursuant to this Agreement and the Merger shall be an
exempt transaction for purposes of Section 16.

                                  ARTICLE III.

             REPRESENTATIONS AND WARRANTIES OF ANADARKO AND SUBCORP

                  In order to induce UPR to enter into this Agreement, Anadarko
and Subcorp hereby represent and warrant to UPR that the statements contained in
this Article III are true, correct and complete.

                  3.1 Organization and Standing. Each of Anadarko and Subcorp is
a corporation duly organized, validly existing and in good standing under the
laws of its state of incorporation with full corporate power and authority to
own, lease, use and operate its properties and to conduct its business as and
where now owned, leased, used, operated and conducted. Each of Anadarko and
Subcorp, and each subsidiary of Anadarko, is duly qualified to do business and
is in good standing in each jurisdiction in which the nature of the business
conducted by it or the property it owns, leases or operates, requires it to so
qualify, except where the failure to be so qualified or in good standing in such
jurisdiction would not have a Material Adverse Effect (as defined in Section
8.3) on Anadarko or Subcorp, as the case may be. Anadarko is not in default in
the performance, observance or fulfillment of any provision of the Anadarko
Restated Certificate of Incorporation, as amended (the "Anadarko Certificate"),
or the Anadarko By-Laws, as amended (the "Anadarko By-Laws"), and Subcorp is not
in default in the performance, observance or fulfillment of any provisions of
its Articles of Incorporation or By-laws. Anadarko has heretofore furnished to
UPR a complete and correct copy of (i) the


                                      -7-
<PAGE>   12

Anadarko Certificate and the Anadarko By-Laws, each as in effect as of the date
of this Agreement, and (ii) the Articles of Incorporation of Subcorp and the
By-laws of Subcorp.

                  3.2 Subsidiaries and Investments. Anadarko does not own,
directly or indirectly, any equity or other ownership interest in any
corporation, partnership, joint venture or other entity or enterprise, except
for the subsidiaries, as set forth in Section 3.2 to the disclosure schedule
delivered by Anadarko to UPR and dated the date hereof (the "Anadarko Disclosure
Schedule"), Anadarko owns, directly or indirectly, each of the outstanding
shares of capital stock (or other ownership interests having by their terms
ordinary voting power to elect a majority of directors or others performing
similar functions with respect to such subsidiary) of each of Anadarko's
subsidiaries. Each of the outstanding shares of capital stock of each of
Anadarko's subsidiaries is duly authorized, validly issued, fully paid and
nonassessable, and is owned, directly or indirectly, by Anadarko free and clear
of all liens, pledges, security interests, claims or other encumbrances. There
are no outstanding subscriptions, options, warrants, puts, calls, agreements,
understandings, claims or other commitments or rights of any type relating to
the issuance, sale or transfer of any securities of any subsidiary of Anadarko,
nor are there outstanding any securities that are convertible into or
exchangeable for any shares of capital stock of any subsidiary of Anadarko, and
neither Anadarko nor any subsidiary of Anadarko has any obligation of any kind
to issue any additional securities or to pay for or repurchase any securities of
any subsidiary of Anadarko or any predecessor thereof.

                  3.3 Corporate Power and Authority. Each of Anadarko and
Subcorp has all requisite corporate power and authority to enter into and
deliver this Agreement, subject to approval of the issuance of Anadarko Common
Shares issuable in the Merger and the transactions contemplated hereby by the
holders of Anadarko Common Shares (the "Anadarko Stockholders") (the "Share
Issuance"), to perform its obligations hereunder and to consummate the
transactions contemplated by this Agreement. The execution and delivery of this
Agreement and the consummation of the transactions contemplated hereby by
Anadarko and Subcorp have been duly authorized by all necessary corporate action
on the part of each of Anadarko and Subcorp, subject to approval by the Anadarko
Stockholders of the Share Issuance. This Agreement has been duly executed and
delivered by each of Anadarko and Subcorp, and constitutes the legal, valid and
binding obligation of each of Subcorp and Anadarko enforceable against each of
them in accordance with its terms.

                  3.4 Capitalization of Anadarko and Subcorp.

                  (a) As of March 31, 2000, Anadarko's authorized capital stock
consisted solely of (A) 300,000,000 shares of common stock, $0.10 par value
("Anadarko Common Shares"), of which (i) 130,079,024 shares were issued and
outstanding, (ii) no shares were issued and held in treasury (which does not
include Anadarko Common Shares reserved for issuance as set forth in clause
(iii)), (iii) 26,106,400 shares were reserved for issuance upon the exercise or
conversion of options, warrants or convertible securities granted or issuable by
Anadarko and (iv) 25,885,726 Anadarko Common Shares were reserved for future
issuance under the Stock Option Agreement dated April 2, 2000, between UPR and
Anadarko (the "Anadarko Stock Option Agreement"), and (B) 2,000,000 shares of
Preferred Stock, $1.00 par value, of which (i) 200,000 shares of 5.46% Series B
Cumulative Preferred Stock were issued and outstanding and (ii) 200,000 shares
have been designated as Series C Junior Participating Preferred Stock were


                                      -8-
<PAGE>   13

reserved for issuance pursuant to the rights issued under the Agreement, dated
as of October 29, 1998, between Anadarko and the Chase Manhattan Bank, as rights
agent (the "Anadarko Rights Agreement"). Each outstanding share of Anadarko
capital stock is, and all Anadarko Common Shares to be issued in connection with
the Merger will be, duly authorized and validly issued, fully paid and
nonassessable, and each outstanding share of Anadarko capital stock has not
been, and all Anadarko Common Shares to be issued in connection with the Merger
will not be, issued in violation of any preemptive or similar rights. As of the
date hereof, other than as set forth in the first sentence hereof, in Section
3.4 to the Anadarko Disclosure Schedule or as contemplated by the Anadarko Stock
Option Agreement, there are no outstanding subscriptions, options, warrants,
puts, calls, agreements, understandings, claims or other commitments or rights
of any type relating to the issuance, sale, repurchase, transfer or registration
by Anadarko of any equity securities of Anadarko, nor are there outstanding any
securities that are convertible into or exchangeable for any shares of capital
stock of Anadarko and Anadarko has no obligation of any kind to issue any
additional securities. The issuance and sale of all of the shares of capital
stock described in this Section 3.3(a) have been in compliance with federal and
state securities laws. The Anadarko Common Shares (including those Anadarko
Common Shares to be issued in the Merger) are registered under the Exchange Act.
Other than pursuant to the Anadarko Stock Option Agreement, Anadarko has not
agreed to register any securities under the Securities Act or under any state
securities law or granted registration rights to any person or entity (which
rights are currently exerciseable).

                  (b) Subcorp's authorized capital stock consists solely of
1,000 shares of Subcorp Common Stock, of which, as of the date hereof, 100
shares were issued and outstanding and none were reserved for issuance. As of
the date hereof, all of the outstanding shares of Subcorp Common Stock are owned
free and clear of any liens, claims or encumbrances by Anadarko.

                  3.5 Conflicts; Consents and Approval. Neither the execution
and delivery of this Agreement by Anadarko or Subcorp, or the Anadarko Stock
Option Agreement by Anadarko, nor the consummation of the transactions
contemplated hereby will:

                  (a) conflict with, or result in a breach of any provision of
the Anadarko Certificate or the Anadarko By-laws or the Articles of
Incorporation or By-laws of Subcorp;

                  (b) violate, or conflict with, or result in a breach of any
provision of, or constitute a default (or an event that, with the giving of
notice, the passage of time or otherwise, would constitute a default) under, or
entitle any party (with the giving of notice, the passage of time or otherwise)
to terminate, accelerate, modify or call a default under, or result in the
creation of any lien, security interest, charge or encumbrance upon any of the
properties or assets of Anadarko or any of its subsidiaries under, any of the
terms, conditions or provisions of any note, bond, mortgage, indenture, deed of
trust, license, contract, undertaking, agreement, lease or other instrument or
obligation to which Anadarko or any of its subsidiaries is a party;

                  (c) violate any order, writ, injunction, decree, statute, rule
or regulation applicable to Anadarko or any of its subsidiaries or any of their
respective properties or assets; or



                                      -9-
<PAGE>   14

                  (d) require any action or consent or approval of, or review
by, or registration or filing by Anadarko or any of its affiliates with, any
third party or any local, domestic, foreign or multi-national court, arbitral
tribunal, administrative agency or commission or other governmental or
regulatory body, agency, instrumentality or authority (a "Governmental
Authority"), other than (i) approval by the Anadarko Stockholders of the Share
Issuance, (ii) authorization for inclusion of the Anadarko Common Shares to be
issued in the Merger and the transactions contemplated hereby on the NYSE,
subject to official notice of issuance, (iii) actions required by the
Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended (together with
the rules and regulations thereunder, the "HSR Act"), (iv) registrations or
other actions required under federal and state securities laws as are
contemplated by this Agreement, or (v) consents or approvals of any Governmental
Authority set forth in Section 3.5 to the Anadarko Disclosure Schedule;

except in the case of clauses (b), (c) and (d) for any of the foregoing that
would not, individually or in the aggregate, have a Material Adverse Effect on
Anadarko or a material adverse effect on the ability of the parties hereto to
consummate the transactions contemplated hereby.

                  3.6 Brokerage and Finder's Fees. Except as set forth in
Section 3.6 to the Anadarko Disclosure Schedule, neither Anadarko nor any
stockholder, director, officer or employee thereof has incurred or will incur on
behalf of Anadarko any financial advisory, brokerage, finder's or similar fee in
connection with the transactions contemplated by this Agreement. Copies of all
agreements relating to such obligations have been provided to UPR.

                  3.7 Reorganization. To the knowledge of Anadarko and Subcorp,
neither Anadarko nor Subcorp, nor any of their affiliates has taken or agreed to
take any action that (without giving effect to any actions taken or agreed to be
taken by UPR or any of its affiliates) would prevent the Merger from
constituting a "reorganization" qualifying under the provisions of Section
368(a) of the Code.

                  3.8 No Material Adverse Change. Except as disclosed in the
Anadarko SEC Documents filed prior to the date of this Agreement, since January
1, 2000, there has been no material adverse change in the business, assets,
liabilities, results of operations, financial condition or prospects of Anadarko
and its subsidiaries taken as a whole, or any event, occurrence or development
that would reasonably be expected to have a Material Adverse Effect on Anadarko
or a material adverse effect on the ability of Anadarko to consummate the
transactions contemplated hereby.

                  3.9 Anadarko SEC Documents. Anadarko has timely filed with the
Commission all forms, reports, schedules, statements and other documents
required to be filed by it since January 1, 1997 under the Exchange Act or the
Securities Act (such documents, as supplemented and amended since the time of
filing, collectively, the "Anadarko SEC Documents"). The Anadarko SEC Documents,
including, without limitation, any financial statements or schedules included
therein, at the time filed (and, in the case of registration statements and
proxy statements, on the dates of effectiveness and the dates of mailing,
respectively and, in the case of any Anadarko SEC Document amended or superseded
by a filing prior to the date of this Agreement, then on the date of such
amending or superseding filing) (a) did not contain any untrue statement of a
material fact or omit to state a material fact required to


                                      -10-
<PAGE>   15

be stated therein or necessary in order to make the statements therein, in light
of the circumstances under which they were made, not misleading, and (b)
complied in all material respects with the applicable requirements of the
Exchange Act and the Securities Act, as the case may be. The financial
statements of Anadarko included in the Anadarko SEC Documents at the time filed
(and, in the case of registration statements and proxy statements, on the dates
of effectiveness and the dates of mailing, respectively, and, in the case of any
Anadarko SEC Document amended or superseded by a filing prior to the date of
this Agreement, then on the date of such amending or superseding filing)
complied as to form in all material respects with applicable accounting
requirements and with the published rules and regulations of the Commission with
respect thereto, were prepared in accordance with generally accepted accounting
principles applied on a consistent basis during the periods involved (except as
may be indicated in the notes thereto or, in the case of unaudited statements,
as permitted by Form 10-Q of the Commission), and fairly present (subject, in
the case of unaudited statements, to normal, recurring audit adjustments) the
consolidated financial position of Anadarko and its consolidated subsidiaries as
at the dates thereof and the consolidated results of their operations and cash
flows for the periods then ended. No subsidiary of Anadarko is subject to the
periodic reporting requirements of the Exchange Act or required to file any
form, report or other document with the Commission, the NYSE, any other stock
exchange or any other comparable Governmental Authority.

                  3.10 Taxes.

                  (a) Anadarko and its subsidiaries have duly filed all material
federal, state, local and foreign income, franchise, excise, real and personal
property and other Tax Returns (as defined below) (including, but not limited
to, those filed on a consolidated, combined or unitary basis) required to have
been filed by Anadarko or its subsidiaries prior to the date hereof. All of the
foregoing Tax Returns and reports are true and correct (except for such
inaccuracies that are, individually or in the aggregate, immaterial), and
Anadarko and its subsidiaries have within the time and manner prescribed by
Applicable Law paid or, prior to the Effective Time, will pay all Taxes (as
defined below), interest and penalties required to be paid in respect of the
periods covered by such returns or reports or otherwise due to any federal,
state, foreign, local or other taxing authority. Except as set forth in Section
3.10 to the Anadarko Disclosure Schedule, neither Anadarko nor any of its
subsidiaries have any material liability for any Taxes in excess of the amounts
so paid or reserves so established and neither Anadarko nor any of its
subsidiaries is delinquent in the payment of any material Tax. Except as set
forth in Section 3.10 to the Anadarko Disclosure Schedule, neither Anadarko nor
any of its subsidiaries has requested or filed any document having the effect of
causing any extension of time within which to file any returns in respect of any
fiscal year which have not since been filed. No deficiencies for any material
Tax have been proposed in writing, asserted or assessed (tentatively or
definitely), in each case, by any taxing authority, against Anadarko or any of
its subsidiaries for which there are not adequate reserves. Neither Anadarko nor
any of its subsidiaries is the subject of any currently ongoing Tax audit except
for those that are, individually or in the aggregate, immaterial. There are no
pending requests for waivers of the time to assess any material Tax, other than
those made in the ordinary course and for which payment has been made or there
are adequate reserves. Except as set forth in Section 3.10 to the Anadarko
Disclosure Schedule, neither Anadarko nor any of its subsidiaries has waived any
statute of limitations in respect of Taxes or agreed to any extension of time
with respect to a Tax assessment or deficiency. There



                                      -11-
<PAGE>   16

are no liens with respect to material Taxes upon any of the properties or
assets, real or personal, tangible or intangible of Anadarko or any of its
subsidiaries (other than liens for Taxes not yet due). To the knowledge of
Anadarko, no claim has ever been made in writing by an authority in a
jurisdiction where none of Anadarko and its subsidiaries files Tax Returns that
Anadarko or any of its subsidiaries is or may be subject to taxation by that
jurisdiction. Neither Anadarko nor any of its subsidiaries has filed an election
under Section 341(f) of the Code to be treated as a consenting corporation.

                  (b) Except as set forth in Section 3.10 to the Anadarko
Disclosure Schedule, neither Anadarko nor any of its subsidiaries is obligated
by any contract, agreement or other arrangement to indemnify any other person
with respect to material Taxes. Except as set forth in Section 3.10 to the
Anadarko Disclosure Schedule, neither Anadarko nor any of its subsidiaries are
now or have ever been a party to or bound by any agreement or arrangement
(whether or not written and including, without limitation, any arrangement
required or permitted by law) binding Anadarko or any of its subsidiaries that
(i) requires Anadarko or any of its subsidiaries to make any Tax payment to or
for the account of any other person, (ii) affords any other person the benefit
of any net operating loss, net capital loss, investment Tax credit, foreign Tax
credit, charitable deduction or any other credit or Tax attribute which could
reduce Taxes (including, without limitation, deductions and credits related to
alternative minimum Taxes) of Anadarko or any of its subsidiaries, or (iii)
requires or permits the transfer or assignment of income, revenues, receipts or
gains to Anadarko or any of its subsidiaries, from any other person.

                  (c) Anadarko and its subsidiaries have withheld and paid all
material Taxes required to have been withheld and paid in connection with
amounts paid or owing to any employee, independent contractor, creditor,
shareholder or other third party.

                  (d) Neither Anadarko nor any of its subsidiaries is
responsible for any material Taxes of any other person (other than that of
Anadarko and its subsidiaries) under Treasury Regulation Section 1.1502-6 (or
any similar provision of state, local, or foreign law), as a transferee, by
contract, or otherwise.

                  (e) Neither Anadarko nor any of its subsidiaries has
constituted either a "distributing corporation" or a "controlled corporation"
(within the meaning of Section 355(a)(1)(A) of the Code) in a distribution of
stock intended to qualify for tax-free treatment under Section 355 of the Code
(i) in the two years prior to the date of this Agreement (or will constitute
such a corporation in the two years prior to the date of the Effective Time) or
(ii) in a distribution which otherwise constitutes part of a "plan" or "series
of related transactions" (within the meaning of Section 355(e) of the Code) in
conjunction with the Merger.

                  (f) "Tax Returns" means returns, reports and forms required to
be filed with any Governmental Authority of the United States or any other
jurisdiction responsible for the imposition or collection of Taxes.

                  (g) "Taxes" means (i) all taxes (whether federal, state, local
or foreign) based upon or measured by income and any other tax whatsoever,
including, without limitation, gross receipts, profits, sales, use, occupation,
value added, ad valorem, transfer, franchise, withholding, payroll, employment,
excise, or property taxes, together with any interest or



                                      -12-
<PAGE>   17

penalties imposed with respect thereto and (ii) any obligations under any
agreements or arrangements with respect to any taxes described in clause (i)
above.

                  3.11 Compliance with Law. Anadarko is in compliance, and at
all times since January 1, 1997 has been in compliance, with all applicable
laws, statutes, orders, rules, regulations, policies or guidelines promulgated,
or judgments, decisions or orders entered by any Governmental Authority
(collectively, "Applicable Laws") relating to Anadarko or its business or
properties, except where the failure to be in compliance with such Applicable
Laws, individually or in the aggregate, would not reasonably be expected to have
a Material Adverse Effect on Anadarko. Except as set forth in Section 3.11 to
the Anadarko Disclosure Schedule, to the knowledge of Anadarko, no investigation
or review by any Governmental Authority with respect to Anadarko or its
subsidiaries is pending or threatened, nor has any Governmental Authority
indicated in writing an intention to conduct the same, other than those the
outcome of which would not reasonably be expected to have a Material Adverse
Effect on Anadarko.

                  3.12 Registration Statement; Joint Proxy Statement. None of
the information provided by Anadarko for inclusion in the registration statement
on Form S-4 (such registration statement as amended, supplemented or modified,
the "Registration Statement") to be filed with the Commission by Anadarko under
the Securities Act, including the prospectus relating to Anadarko Common Shares
to be issued in the Merger (as amended, supplemented or modified, the
"Prospectus") and the joint proxy statement and form of proxies relating to the
vote of UPR Stockholders with respect to the Merger and the vote of Anadarko
Stockholders with respect to the Share Issuance (as amended, supplemented or
modified, the "Joint Proxy Statement"), at the time the Registration Statement
becomes effective or, in the case of the Joint Proxy Statement, at the date of
mailing and at the date of the UPR Stockholders Meeting (as defined in Section
5.3(a)) or the Anadarko Stockholders Meeting (as defined in Section 5.2(a)) to
consider the Merger and the transactions contemplated thereby, will contain any
untrue statement of a material fact or omit to state any material fact required
to be stated therein or necessary in order to make the statements therein, in
light of the circumstances under which they are made, not misleading. The
Registration Statement and Joint Proxy Statement, except for such portions
thereof that relate only to UPR or its subsidiaries, will each comply as to form
in all material respects with the provisions of the Securities Act and the
Exchange Act.

                  3.13 Litigation. Except as set forth in Section 3.13 to the
Anadarko Disclosure Schedule, there is no suit, claim, action, proceeding,
hearing, notice of violation, demand letter or investigation (an "Action")
pending or, to the knowledge of Anadarko (or its executive officers or
directors), threatened against Anadarko or any executive officer or director of
Anadarko that, individually or in the aggregate, would reasonably be expected to
have a Material Adverse Effect on Anadarko or a material adverse effect on the
ability of Anadarko to consummate the transactions contemplated hereby. Anadarko
is not subject to any outstanding order, writ, injunction or decree that,
individually or in the aggregate, insofar as can be reasonably foreseen, would
have a Material Adverse Effect on Anadarko or a material adverse effect on the
ability of Anadarko to consummate the transactions contemplated hereby.


                                      -13-
<PAGE>   18

                  3.14 Anadarko Employee Benefit Plans.

                  (a) For purposes of this Agreement, the following terms have
the definitions given below:

                  "Anadarko Controlled Group Liability" means any and all
         liabilities (i) under Title IV of ERISA, (ii) under section 302 of
         ERISA, (iii) under sections 412 and 4971 of the Code, (iv) as a result
         of a failure to comply with the continuation coverage requirements of
         section 601 et seq. of ERISA and section 4980B of the Code, and (v)
         under corresponding or similar provisions of foreign laws or
         regulations, other than such liabilities that arise solely out of, or
         relate solely to, the Anadarko Employee Benefit Plans listed in Section
         3.14 of the Anadarko Disclosure Schedule.

                  "Anadarko Employee Benefit Plans" means any Anadarko Employee
         Benefit Plans, program, policy, practices, or other arrangement
         providing benefits to any current or former employee, officer or
         director of Anadarko or any of its subsidiaries or any beneficiary or
         dependent thereof that is sponsored or maintained by Anadarko or any of
         its subsidiaries or to which Anadarko or any of its subsidiaries
         contributes or is obligated to contribute, whether or not written,
         including without limitation any employee welfare benefit plan within
         the meaning of Section 3(1) of ERISA, any employee pension benefit plan
         within the meaning of Section 3(2) of ERISA (whether or not such plan
         is subject to ERISA) and any bonus, incentive, deferred compensation,
         vacation, stock purchase, stock option, severance, employment, change
         of control or fringe benefit plan, program or agreement.

                  "Anadarko Employment Agreement" means a contract, offer letter
         or agreement of Anadarko or any subsidiary with or addressed to any
         individual who is rendering or has rendered services thereto as an
         employee or consultant pursuant to which Anadarko or any subsidiary has
         any actual or contingent liability or obligation to provide
         compensation and/or benefits in consideration for past, present or
         future services.

                  "Anadarko Material Employment Agreement" means an Anadarko
         Employment Agreement pursuant to which Anadarko or any subsidiary has
         or could have any obligation to provide compensation and/or benefits
         (including without limitation severance pay or benefits) in an amount
         or having a value in excess of $100,000 per year or $500,000 in the
         aggregate.

                  "Anadarko Plan" means any Anadarko Employee Benefit Plans
         other than a Multiemployer Plan.

                  "ERISA Affiliate" means, with respect to any entity, trade or
         business, any other entity, trade or business that is a member of a
         group described in Section 414(b), (c), (m) or (o) of the Code or
         Section 4001(b)(1) of ERISA that includes the first entity, trade or
         business, or that is a member of the same "controlled group" as the
         first entity, trade or business pursuant to Section 4001(a)(14) of
         ERISA.

                  "Multiemployer Plan" means any "multiemployer plan" within the
         meaning of Section 4001(a)(3) of ERISA.


                                      -14-
<PAGE>   19

                  "Withdrawal Liability" means liability to a Multiemployer Plan
         as a result of a complete or partial withdrawal from such Multiemployer
         Plan, as those terms are defined in Part I of Subtitle E of Title IV of
         ERISA.

                  (a) Section 3.14(a) to the Anadarko Disclosure Schedule
includes a complete list of all material Anadarko Employee Benefit Plans and all
Anadarko Material Employment Agreements.

                  (b) With respect to each Anadarko Plan, Anadarko has delivered
or made available to UPR a true, correct and complete copy of: (i) each writing
constituting a part of such Anadarko Plan, including without limitation all plan
documents, employee communications, benefit schedules, trust agreements, and
insurance contracts and other funding vehicles; (ii) the most recent Annual
Report (Form 5500 Series) and accompanying schedule, if any; (iii) the current
summary plan description and any material modifications thereto, if any (in each
case, whether or not required to be furnished under ERISA); (iv) the most recent
annual financial report, if any; (v) the most recent actuarial report, if any;
and (vi) the most recent determination letter from the Internal Revenue Service,
if any. Anadarko has delivered or made available to UPR a true, complete and
correct copy of each Anadarko Material Employment Agreement. Except as
specifically provided in the foregoing documents delivered or made available to
UPR, there are no amendments to any Anadarko Plan or Anadarko Material
Employment Agreement that have been adopted or approved nor has Anadarko or any
of its subsidiaries undertaken to make any such amendments or to adopt or
approve any new Anadarko Plan or Anadarko Material Employment Agreement.

                  (c) Section 3.14(c) to the Anadarko Disclosure Schedule
identifies each Anadarko Plan that is intended to be a "qualified plan" within
the meaning of Section 401(a) of the Code ("Anadarko Qualified Plans"). The
Internal Revenue Service has issued a favorable determination letter with
respect to each Anadarko Qualified Plan and the related trust that has not been
revoked, and there are no circumstances and, to the knowledge of Anadarko, no
events have occurred that could adversely affect the qualified status of any
Anadarko Qualified Plan or the related trust. Section 3.14(c) to the Anadarko
Disclosure Schedule identifies each Anadarko Plan which is intended to meet the
requirements of Code Section 501(c)(9), and each such plan meets such
requirements.

                  (d) All material contributions required to be made to any
Anadarko Plan by applicable law or regulation or by any plan document or other
contractual undertaking, and all material premiums due or payable with respect
to insurance policies funding any Anadarko Plan, for any period through the date
hereof have been timely made or paid in full or, to the extent not required to
be made or paid on or before the date hereof, either (i) have been fully
reflected on the financial statements included in the Anadarko SEC Documents, or
(ii) items omitted from the Anadarko SEC Documents could not reasonably be
expected to have a Material Adverse Effect on Anadarko. Each Anadarko Employee
Benefit Plan that is an employee welfare benefit plan under Section 3(1) of
ERISA is either (i) funded through an insurance company contract and is not a
"welfare benefit fund" with the meaning of Section 419 of the Code or (ii)
unfunded.

                  (e) Except as set forth in Section 3.13(e) to the Anadarko
Disclosure Schedule, with respect to each Anadarko Employee Benefit Plan,
Anadarko and its subsidiaries


                                      -15-
<PAGE>   20


have complied, and are now in compliance, in all material respects, with all
provisions of ERISA, the Code and all laws and regulations applicable to such
Anadarko Employee Benefit Plans and each Anadarko Employee Benefit Plan has been
administered in all material respects in accordance with its terms. There is not
now, nor, to the knowledge of Anadarko, do any circumstances currently exist
that could give rise to, any requirement for the posting of security with
respect to an Anadarko Plan or the imposition of any lien on the assets of
Anadarko or any of its subsidiaries under ERISA or the Code.

                  (f) With respect to each Anadarko Plan that is subject to
Title IV or Section 302 of ERISA or Section 412 or 4971 of the Code: (i) there
does not exist any accumulated funding deficiency within the meaning of Section
412 of the Code or Section 302 of ERISA, whether or not waived; (ii) no
reportable event within the meaning of Section 4043(c) of ERISA for which the
30-day notice requirement has not been waived has occurred, and the consummation
of the transactions contemplated by this agreement will not result in the
occurrence of any such reportable event; (iii) all premiums to the Pension
Benefit Guaranty Corporation (the "PBGC") have been timely paid in full; (iv) no
liability (other than for premiums to the PBGC) under Title IV of ERISA has been
or is expected to be incurred by Anadarko or any of its subsidiaries; and (v)
the PBGC has not instituted proceedings to terminate any such Anadarko Plan and,
to Anadarko's knowledge, no condition exists that presents a risk that such
proceedings will be instituted or which would constitute grounds under Section
4042 of ERISA for the termination of, or the appointment of a trustee to
administer, any such Anadarko Plan.

                  (g) (i) No Anadarko Employee Benefit Plan is a Multiemployer
Plan or a plan that has two or more contributing sponsors at least two of whom
are not under common control, within the meaning of Section 4063 of ERISA (a
"Multiple Employer Plan"); (ii) none of Anadarko and its subsidiaries nor any of
their respective ERISA Affiliates has, at any time during the last six years,
contributed to or been obligated to contribute to any Multiemployer Plan or
Multiple Employer Plan; and (iii) none of Anadarko and its subsidiaries nor any
of their respective ERISA Affiliates has incurred any material Withdrawal
Liability that has not been satisfied in full. With respect to each Anadarko
Plan that is a Multiemployer Plan: (i) if Anadarko or any of its subsidiaries or
any of their respective ERISA Affiliates were to experience a withdrawal or
partial withdrawal from such plan, no material Withdrawal Liability would be
incurred; and (ii) none of Anadarko and its subsidiaries, nor any of their
respective ERISA Affiliates has received any notification, nor does Anadarko
have any knowledge, that any such Anadarko Plan is in reorganization, has been
terminated, is insolvent, or may reasonably be expected to be in reorganization,
to be insolvent, or to be terminated.

                  (h) There does not now exist, nor, to the knowledge of
Anadarko, do any circumstances exist that could reasonably be expected to result
in, any material Anadarko Controlled Group Liability that would be a liability
of Anadarko or any of its subsidiaries following the Closing. Without limiting
the generality of the foregoing, neither Anadarko nor any of its subsidiaries,
nor any of their respective ERISA Affiliates, has engaged in any transaction
described in Section 4069 or Section 4204 or 4212 of ERISA.

                  (i) Section 3.14(i) to the Anadarko Disclosure Schedule sets
forth a list of each Anadarko Employment Agreement under which the execution and
delivery of this


                                      -16-
<PAGE>   21


Agreement or the consummation of the transactions contemplated hereby could
(either alone or in conjunction with any other event) result in, cause the
accelerated vesting, funding or delivery of, or materially increase the amount
or value of, any payment or benefit to any employee, officer or director of
Anadarko or any of its subsidiaries, or could limit the right of Anadarko or any
of its subsidiaries to amend, merge, terminate or receive a reversion of assets
from any Anadarko Employee Benefit Plan or related trust or any Anadarko
Material Employment Agreement or related trust.

                  (j) None of Anadarko and its subsidiaries nor, to the
knowledge of Anadarko, any other person, including any fiduciary, has engaged in
any "prohibited transaction" (as defined in Section 4975 of the Code or Section
406 of ERISA), which could subject any of the Anadarko Employee Benefit Plans or
their related trusts, Anadarko, any of its subsidiaries or any person that
Anadarko or any of its subsidiaries has an obligation to indemnify, to any
material tax or material penalty imposed under Section 4975 of the Code or
Section 502 of ERISA.

                  (k) Except as set forth in Section 3.14(k) to the Anadarko
Disclosure Schedule, there are no pending or threatened claims (other than
claims for benefits in the ordinary course), lawsuits or arbitrations which have
been asserted or instituted, and to Anadarko's knowledge, no set of
circumstances exists which may reasonably give rise to a claim or lawsuit,
against the Anadarko Plans, any fiduciaries thereof with respect to their duties
to the Anadarko Plans or the assets of any of the trusts under any of the
Anadarko Plans which could reasonably be expected to result in any material
liability of Anadarko or any of its subsidiaries to the PBGC, the Department of
Treasury, the Department of Labor, any Multiemployer Plan, any Anadarko Plan or
any participant in an Anadarko Plan.

                  (l) Anadarko, its subsidiaries and each member of their
respective business enterprises have in all material respects complied with the
Worker Adjustment and Retraining Notification Act and in all material respects,
with all similar state, local and foreign laws.

                  (m) All Anadarko Employee Benefit Plans subject to the laws of
any jurisdiction outside of the United States (i) have been maintained in
accordance with all applicable requirements, (ii) if they are intended to
qualify for special tax treatment, meet all requirements for such treatment, and
(iii) if they are intended to be funded and/or book-reserved are funded and/or
book-reserved in all material respects, as appropriate, based upon reasonable
actuarial assumptions.

                  3.15 Contracts. All written or oral contracts, agreements,
guarantees, leases and executory commitments other than Anadarko Plans to which
Anadarko or its subsidiaries is a party or by which its assets are bound which
are material to Anadarko (each an "Anadarko Contract"), are valid and binding
obligations of Anadarko and, to the knowledge of Anadarko, the valid and binding
obligation of each other party thereto except such Anadarko Contracts that if
not so valid and binding would not, individually or in the aggregate, have a
Material Adverse Effect on Anadarko. Neither Anadarko nor, to the knowledge of
Anadarko, any other party thereto is in violation of or in default in respect
of, nor has there occurred an event or condition that with the passage of time
or giving of notice (or both) would constitute a default under or permit the
termination of, any such Anadarko Contract except such violations or defaults
under



                                      -17-
<PAGE>   22

or terminations that, individually or in the aggregate, would not have a
Material Adverse Effect on Anadarko.

                  3.16 Labor Matters. Anadarko does not have any labor contracts
or collective bargaining agreements with any persons employed by Anadarko or any
persons otherwise performing services primarily for Anadarko. There is no labor
strike, dispute or stoppage pending or, to the knowledge of Anadarko, threatened
against Anadarko, and Anadarko has not experienced any labor strike, dispute or
stoppage or other material labor difficulty involving its employees since
January 1, 1998. To the knowledge of Anadarko, since January 1, 1998, no
campaign or other attempt for recognition has been made by any labor
organization or employees with respect to employees of Anadarko or any of its
subsidiaries.

                  3.17 Undisclosed Liabilities. Except (i) as and to the extent
disclosed or reserved against on the balance sheet of Anadarko as of December
31, 1999 included in the Anadarko SEC Documents, or (ii) as incurred after the
date thereof in the ordinary course of business consistent with prior practice
and not prohibited by this Agreement, Anadarko does not have any liabilities or
obligations of any nature, whether absolute, accrued, contingent or otherwise
and whether due or to become due, that, individually or in the aggregate, have
had or would reasonably be expected to have a Material Adverse Effect on
Anadarko.

                  3.18 Permits; Compliance. Anadarko is in possession of all
material franchises, grants, authorizations, licenses, permits, easements,
variances, exemptions, consents, certificates, approvals and orders necessary to
own, lease and operate its properties and to carry on its business as it is now
being conducted (collectively, the "Anadarko Permits"), and there is no Action
pending or, to the knowledge of Anadarko, threatened regarding any of the
Anadarko Permits. Anadarko is not in conflict with, or in default or violation
of any of the Anadarko Permits, except for any such conflicts, defaults or
violations which, individually or in the aggregate, could not reasonably be
expected to have a Material Adverse Effect on Anadarko.

                  3.19 Environmental Matters. Except as disclosed in the
Anadarko SEC Documents, (i) the properties, operations and activities of
Anadarko and its subsidiaries are in compliance with all applicable
Environmental Laws (as defined below) and all past noncompliance of Anadarko or
any Anadarko subsidiary with any Environmental Laws or Environmental Permits (as
defined below), has been resolved without any pending, ongoing or future
obligation, cost or liability; (ii) Anadarko and its subsidiaries and the
properties and operations of Anadarko and its subsidiaries are not subject to
any existing, pending or, to the knowledge of Anadarko, threatened Action by or
before any court or Governmental Authority under any Environmental Law; (iii)
except as allowed by Environmental Permits or Environmental Laws, there has been
no release of any hazardous substance, pollutant or contaminant into the
environment by Anadarko or its subsidiaries or in connection with their
properties or operations; and (iv) except as allowed by Environmental Permits or
Environmental Laws, there has been no exposure of any person or property to any
hazardous substance, pollutant or contaminant in connection with the properties,
operations and activities of Anadarko and its subsidiaries, in each case, other
than those matters that, individually or in the aggregate, would not reasonably
be expected to have a Material Adverse Effect on Anadarko. The term
"Environmental Laws" means all federal, state, local or foreign laws relating to
pollution, or protection of human health from Hazardous Materials (as defined
below) or the environment


                                      -18-
<PAGE>   23

(including, without limitation, ambient air, surface water, groundwater, land
surface or subsurface strata), including, without limitation, laws relating to
emissions, discharges, releases or threatened releases of chemicals, pollutants,
contaminants, or industrial, toxic or hazardous substances or wastes
(collectively, "Hazardous Materials") into the environment, or otherwise
relating to the manufacture, processing, distribution, use, treatment, storage,
disposal, transport or handling of Hazardous Materials, as well as all
authorizations, codes, decrees, injunctions, judgments, licenses, notices,
orders, permits, plans or regulations issued, entered, promulgated or approved
thereunder. "Environmental Permit" means any permit, approval, license or other
authorization required under or issued pursuant to any applicable Environmental
Law.

                  3.20 Opinion of Financial Advisor. Anadarko has received the
written opinion of Credit Suisse First Boston Corporation, its financial advisor
(the "Anadarko Financial Advisor"), to the effect that, as of the date of this
Agreement, the Exchange Ratio is fair to Anadarko from a financial point of
view. Anadarko has heretofore provided copies of such opinion to UPR and such
opinion has not been withdrawn or revoked or modified in any material respect.

                  3.21 Board Recommendation; Required Vote. The Board of
Directors of Anadarko, at a meeting duly called and held, has by unanimous vote
of those directors present (i) determined that this Agreement and the
transactions contemplated hereby, including the Merger, and the Anadarko Stock
Option Agreement and the transactions contemplated thereby, taken together, are
fair to and in the best interests of Anadarko and the Anadarko Stockholders, and
(ii) resolved to recommend that the Anadarko Stockholders approve and authorize
the Share Issuance and the Anadarko Board Amendment (as defined in Section
5.2(h)) (the "Anadarko Board Recommendation"). The affirmative vote of holders
of a majority of the Anadarko Common Shares present and voting at the Anadarko
Stockholders Meeting to approve the Share Issuance and the affirmative vote of
holders of 80% of the outstanding Anadarko Common Shares to approve the Anadarko
Board Amendment are the only votes of the Anadarko Stockholders necessary to
adopt this Agreement and approve the transactions contemplated hereby.

                  3.22 State Takeover Laws; Rights Agreement. Prior to the
execution of this Agreement, the Board of Directors of Anadarko has taken all
action necessary to exempt under or make not subject to any state takeover law
or state law that purports to limit or restrict business combinations or the
ability to acquire or vote shares: (i) the execution of this Agreement, and the
Anadarko Stock Option Agreement, (ii) the Merger and (iii) the transactions
contemplated hereby and by the Anadarko Stock Option Agreement. The Anadarko
Rights Agreement has been amended so that UPR is exempt from the definition of
"Acquiring Person" contained in the Anadarko Rights Agreement and no "Shares
Acquisition Date" or "Distribution Date" (as such terms are defined in the
Anadarko Rights Agreement) will occur as a result of the execution of the
Anadarko Stock Option Agreement or the acquisition or transfer of Anadarko
Common Shares by UPR pursuant to the Anadarko Stock Option Agreement. Copies of
all such amendments to the Anadarko Rights Agreement have been previously
provided to UPR.



                                      -19-
<PAGE>   24


                                  ARTICLE IV.

                      REPRESENTATIONS AND WARRANTIES OF UPR

                  In order to induce Subcorp and Anadarko to enter into this
Agreement, UPR hereby represents and warrants to Anadarko and Subcorp that the
statements contained in this Article IV are true, correct and complete, subject
to, in each of the following representations to the specified section of the
disclosure schedule delivered by UPR to Anadarko and dated the date hereof (the
"UPR Disclosure Schedule") provided that items listed in any Section to the UPR
Disclosure Schedule shall apply only to the corresponding section of this
Agreement (except to the extent that there is a specific cross-reference to
another section of the UPR Disclosure Schedule).

                  4.1 Organization and Standing. UPR is a corporation duly
organized, validly existing and in good standing under the laws of the State of
Utah with full corporate power and authority to own, lease, use and operate its
properties and to conduct its business as and where now owned, leased, used,
operated and conducted. Each of UPR and each subsidiary of UPR is duly qualified
to do business and in good standing in each jurisdiction in which the nature of
the business conducted by it or the property it owns, leases or operates
requires it to so qualify, except where the failure to be so qualified or in
good standing in such jurisdiction would not have a Material Adverse Effect on
UPR. UPR is not in default in the performance, observance or fulfillment of any
provision of its Amended and Restated Articles of Incorporation (the "UPR
Articles"), or its By-laws, as in effect on the date hereof (the "UPR Bylaws").
UPR has heretofore furnished to Anadarko a complete and correct copy of the UPR
Articles and the UPR Bylaws.

                  4.2 Subsidiaries and Investments. UPR does not own, directly
or indirectly, any equity or other ownership interest in any corporation,
partnership, joint venture or other entity or enterprise, except for its
subsidiaries and other entities, in each case set forth in Section 4.2 to the
UPR Disclosure Schedule. Section 4.2 of the UPR Disclosure Schedule specifically
identifies each of UPR's "significant subsidiaries" as defined in Rule 1-02(w)
of Regulation S-X (the subsidiaries so identified the "Significant
Subsidiaries"). UPR owns, directly or indirectly, each of the outstanding shares
of capital stock (or other ownership interests having by their terms ordinary
voting power to elect a majority of directors or others performing similar
functions with respect to such subsidiary) of each of UPR's Significant
Subsidiaries. Each of the outstanding shares of capital stock of each of UPR's
Significant Subsidiaries is duly authorized, validly issued, fully paid and
nonassessable, and is owned, directly or indirectly, by UPR free and clear of
all liens, pledges, security interests, claims or other encumbrances. With
respect to UPR's subsidiaries other than the Significant Subsidiaries, to the
extent the outstanding shares of capital stock of each of such Subsidiaries are
not (i) duly authorized, validly issued, fully paid and nonassessable, or (ii)
owned, directly or indirectly, by UPR free and clear of all liens, pledges,
security interests, claims or other encumbrances, there is not, and there could
not reasonably be expected to be, any material impact on the business and
operations of UPR and its subsidiaries taken as a whole. There are no
outstanding subscriptions, options, warrants, puts, calls, agreements,
understandings, claims or other commitments or rights of any type relating to
the issuance, sale or transfer of any securities of any subsidiary of UPR, nor
are there outstanding any securities that are convertible into or exchangeable
for any shares of capital stock of any



                                      -20-
<PAGE>   25

subsidiary of UPR, and neither UPR nor any subsidiary of UPR has any obligation
of any kind to issue any additional securities or to pay for or repurchase any
securities of any subsidiary of UPR or any predecessor thereof.

                  4.3 Corporate Power and Authority. UPR has all requisite
corporate power and authority to enter into and deliver this Agreement, to
perform its obligations hereunder and, subject to authorization of the Merger
and the transactions contemplated hereby by UPR Stockholders, to consummate the
transactions contemplated by this Agreement. The execution and delivery of this
Agreement and the consummation of the transactions contemplated hereby by UPR
have been duly authorized by all necessary corporate action on the part of UPR,
subject to authorization of the Merger and the transactions contemplated hereby
by UPR Stockholders. This Agreement has been duly executed and delivered by UPR
and constitutes the legal, valid and binding obligation of UPR enforceable
against it in accordance with its terms.

                  4.4 Capitalization of UPR. As of March 31, 2000, UPR's
authorized capital stock consisted solely of (a) 400,000,000 shares of common
stock ("UPR Common Stock"), of which (i) 251,952,336 shares were issued and
outstanding, (ii) 4,277,293 shares were issued and held by UPR (which does not
include shares of UPR Common Stock reserved for issuance set forth in clause
(iii) below), (iii) 11,194,329 shares were reserved for issuance upon the
exercise of outstanding UPR Options, and (iv) 50,138,515 shares of UPR Common
Stock were reserved for future issuance under the Stock Option Agreement dated
April 2, 2000 between Anadarko and UPR (the "UPR Stock Option Agreement"); and
(b) 100,000,000 shares of preferred stock, of which (i) none was issued and
outstanding, and (ii) 3,000,000 shares have been designated as Series A Junior
Participating Preferred Stock reserved for issuance pursuant to the rights
issued under the UPR Rights Agreement (as defined in Section 4.22). Since March
31, 2000, UPR has not issued any additional shares of capital stock except for
the issuance of UPR Common Stock in connection with the exercise of UPR Options
and the issuance of UPR Common Stock in respect of awards outstanding on the
date of this Agreement under the Executive Deferred Compensation Plan and the
Deferred Compensation Plan for the Board of Directors. Each outstanding share of
UPR capital stock is duly authorized and validly issued, fully paid and
nonassessable, and has not been issued in violation of any preemptive or similar
rights. Other than as set forth in the first sentence hereof or as contemplated
by the UPR Stock Option Agreement, there are no outstanding subscriptions,
options, warrants, puts, calls, agreements, understandings, claims or other
commitments or rights of any type relating to the issuance, sale, repurchase or
transfer of any securities of UPR, nor are there outstanding any securities
which are convertible into or exchangeable for any shares of capital stock of
UPR, and neither UPR nor any subsidiary of UPR has any obligation of any kind to
issue any additional securities or to pay for or repurchase any securities of
UPR or any predecessor. The issuance and sale of all of the shares of capital
stock described in this Section 4.4 have been in compliance with federal and
state securities laws and the UPR Common Stock is registered under the Exchange
Act. UPR has previously provided Anadarko with a schedule setting forth the
number of shares of each class (including the number of shares issuable upon
exercise of UPR Options and the exercise price and the grant date with respect
thereto) held by all holders of options to purchase UPR capital stock. Other
than pursuant to the UPR Stock Option Agreement, UPR has not agreed to register
any securities under the Securities Act or under any state securities law or
granted registration rights to any person or entity; copies of all such
agreements have previously been provided to Anadarko.


                                      -21-
<PAGE>   26

                  4.5 Conflicts; Consents and Approvals. Neither the execution
and delivery of this Agreement or the UPR Stock Option Agreement by UPR, nor the
consummation of the transactions contemplated hereby or thereby will:

                  (a) conflict with, or result in a breach of any provision of,
         the UPR Articles or the UPR Bylaws;

                  (b) violate, or conflict with, or result in a breach of any
         provision of, or constitute a default (or an event that, with the
         giving of notice, the passage of time or otherwise, would constitute a
         default) under, or entitle any party (with the giving of notice, the
         passage of time or otherwise) to terminate, accelerate, modify or call
         a default under, or result in the creation of any lien, security
         interest, charge or encumbrance upon any of the properties or assets of
         UPR or any of its subsidiaries under, any of the terms, conditions or
         provisions of any note, bond, mortgage, indenture, deed of trust,
         license, contract, undertaking, agreement, lease or other instrument or
         obligation to which UPR or any of its subsidiaries is a party;

                  (c) violate any order, writ, injunction, decree, statute, rule
         or regulation applicable to UPR or any of its subsidiaries or any of
         their respective properties or assets; or

                  (d) require any action or consent or approval of, or review
         by, or registration or filing by UPR or any of its affiliates with, any
         third party or any Governmental Authority, other than (i) authorization
         of the Merger and the transactions contemplated hereby by UPR
         Stockholders, (ii) actions required by the HSR Act, (iii) registrations
         or other actions required under federal and state securities laws as
         are contemplated by this Agreement and (iv) consents or approvals of
         any Governmental Authority;

except in the case of clauses (b), (c) and (d) for any of the foregoing that
would not, individually or in the aggregate, have a Material Adverse Effect on
UPR or a material adverse effect on the ability of the parties hereto to
consummate the transaction contemplated hereby.

                  4.6 Brokerage and Finder's Fees. Except for UPR's obligations
to Goldman, Sachs & Co. and Simmons & Company (the "UPR Financial Advisors")
(copies of all agreements relating to such obligations having previously been
provided to Anadarko), neither UPR nor any stockholder, director, officer or
employee thereof, has incurred or will incur on behalf of UPR, any financial
advisory, brokerage, finder's or similar fee in connection with the transactions
contemplated by this Agreement.

                  4.7 Reorganization. To the knowledge of UPR, neither UPR nor
any of its affiliates has taken or agreed to take any action that (without
giving effect to any actions taken or agreed to be taken by Anadarko or any of
its affiliates) would prevent the Merger from constituting a "reorganization"
qualifying under the provisions of Section 368(a) of the Code.

                  4.8 No Material Adverse Change. As disclosed in the UPR SEC
Documents filed prior to the date of this Agreement, since January 1, 2000,
there has been no material adverse change in the business, assets, liabilities,
results of operations, financial condition or prospects of UPR and its
subsidiaries taken as a whole, or any event, occurrence or development


                                      -22-
<PAGE>   27

that would reasonably be expected to have a Material Adverse Effect on UPR or a
material adverse effect on the ability of UPR to consummate the transactions
contemplated hereby.

                  4.9 UPR SEC Documents. UPR has timely filed with the
Commission all forms, reports, schedules, statements and other documents
required to be filed by it since January 1, 1997 under the Exchange Act or the
Securities Act (such documents, as supplemented and amended since the time of
filing, collectively, the "UPR SEC Documents"). The UPR SEC Documents,
including, without limitation, any financial statements or schedules included
therein, at the time filed (and, in the case of registration statements and
proxy statements, on the dates of effectiveness and the dates of mailing,
respectively and, in the case of any UPR SEC Document amended or superseded by a
filing prior to the date of this Agreement, then on the date of such amending or
superseding filing) (a) did not contain any untrue statement of a material fact
or omit to state a material fact required to be stated therein or necessary in
order to make the statements therein, in light of the circumstances under which
they were made, not misleading, and (b) complied in all material respects with
the applicable requirements of the Exchange Act and the Securities Act, as the
case may be. The financial statements of UPR included in the UPR SEC Documents
at the time filed (and, in the case of registration statements and proxy
statements, on the dates of effectiveness and the dates of mailing,
respectively, and, in the case of any UPR SEC Document amended or superseded by
a filing prior to the date of this Agreement, then on the date of such amending
or superseding filing) complied as to form in all material respects with
applicable accounting requirements and with the published rules and regulations
of the Commission with respect thereto, were prepared in accordance with
generally accepted accounting principles applied on a consistent basis during
the periods involved (except as may be indicated in the notes thereto or, in the
case of unaudited statements, as permitted by Form 10-Q of the Commission), and
fairly present (subject, in the case of unaudited statements, to normal,
recurring audit adjustments) the consolidated financial position of UPR and its
consolidated subsidiaries as at the dates thereof and the consolidated results
of their operations and cash flows for the periods then ended. No subsidiary of
UPR is subject to the periodic reporting requirements of the Exchange Act or
required to file any form, report or other document with the Commission, the
NYSE, any other stock exchange or any other comparable Governmental Authority.

                  4.10 Taxes.

                  (a) UPR and its subsidiaries have duly filed all material
federal, state, local and foreign income, franchise, excise, real and personal
property and other Tax Returns (including, but not limited to, those filed on a
consolidated, combined or unitary basis) required to have been filed by UPR or
its subsidiaries prior to the date hereof. All of the foregoing Tax Returns and
reports are true and correct (except for such inaccuracies that are,
individually or in the aggregate, immaterial), and UPR and its subsidiaries have
within the time and manner prescribed by Applicable Law paid or, prior to the
Effective Time, will pay all Taxes, interest and penalties required to be paid
in respect of the periods covered by such returns or reports or otherwise due to
any federal, state, foreign, local or other taxing authority. Neither UPR nor
any of its subsidiaries have any material liability for any Taxes in excess of
the amounts so paid or reserves so established and neither UPR nor any of its
subsidiaries is delinquent in the payment of any material Tax. Neither UPR nor
any of its subsidiaries has requested or filed any document having the effect of
causing any extension of time within which to file any returns in


                                      -23-
<PAGE>   28

respect of any fiscal year which have not since been filed. No deficiencies for
any material Tax have been proposed in writing, asserted or assessed
(tentatively or definitely), in each case, by any taxing authority, against UPR
or any of its subsidiaries for which there are not adequate reserves. Neither
UPR nor any of its subsidiaries is the subject of any currently ongoing Tax
audit except for those that are, individually or in the aggregate, immaterial.
There are no pending requests for waivers of the time to assess any material
Tax, other than those made in the ordinary course and for which payment has been
made or there are adequate reserves. Neither UPR nor any of its subsidiaries has
waived any statute of limitations in respect of Taxes or agreed to any extension
of time with respect to a Tax assessment or deficiency. There are no liens with
respect to material Taxes upon any of the properties or assets, real or
personal, tangible or intangible of UPR or any of its subsidiaries (other than
liens for Taxes not yet due). To the knowledge of UPR, no claim has ever been
made in writing by an authority in a jurisdiction where none of UPR and its
subsidiaries files Tax Returns that UPR or any of its subsidiaries is or may be
subject to taxation by that jurisdiction. Neither UPR nor any of its
subsidiaries has filed an election under Section 341(f) of the Code to be
treated as a consenting corporation.

                  (b) Neither UPR nor any of its subsidiaries is obligated by
any contract, agreement or other arrangement to indemnify any other person with
respect to material Taxes. Neither UPR nor any of its subsidiaries are now or
have ever been a party to or bound by any agreement or arrangement (whether or
not written and including, without limitation, any arrangement required or
permitted by law) binding UPR or any of its subsidiaries that (i) requires UPR
or any of its subsidiaries to make any Tax payment to or for the account of any
other person, (ii) affords any other person the benefit of any net operating
loss, net capital loss, investment Tax credit, foreign Tax credit, charitable
deduction or any other credit or Tax attribute which could reduce Taxes
(including, without limitation, deductions and credits related to alternative
minimum Taxes) of UPR or any of its subsidiaries, or (iii) requires or permits
the transfer or assignment of income, revenues, receipts or gains to UPR or any
of its subsidiaries, from any other person.

                  (c) UPR and its subsidiaries have withheld and paid all
material Taxes required to have been withheld and paid in connection with
amounts paid or owing to any employee, independent contractor, creditor,
shareholder or other third party.

                  (d) Neither UPR nor any of its subsidiaries is responsible for
any material Taxes of any other person under Treasury Regulation Section
1.1502-6 (or any similar provision of state, local, or foreign law), as a
transferee, by contract, or otherwise.

                  (e) Neither UPR nor any of its subsidiaries has constituted
either a "distributing corporation" or a "controlled corporation" (within the
meaning of Section 355(a)(1)(A) of the Code) in a distribution of stock intended
to qualify for tax-free treatment under Section 355 of the Code (i) in the two
years prior to the date of this Agreement (or will constitute such a corporation
in the two years prior to the date of the Effective Time) or (ii) in a
distribution which otherwise constitutes part of a "plan" or "series of related
transactions" (within the meaning of Section 355(e) of the Code) in conjunction
with the Merger.


                                      -24-
<PAGE>   29

                  4.11 Compliance with Law. UPR is in compliance, and at all
times since January 1, 1997 has been in compliance, with all Applicable Laws
relating to UPR or its business or properties, except where the failure to be in
compliance with such Applicable Laws, individually or in the aggregate, would
not reasonably be expected to have a Material Adverse Effect on UPR. To the
knowledge of UPR, no investigation or review by any Governmental Authority with
respect to UPR is pending or threatened, nor has any Governmental Authority
indicated in writing an intention to conduct the same, other than those the
outcome of which would not reasonably be expected to have a Material Adverse
Effect on UPR.

                  4.12 Registration Statement; Joint Proxy Statement. None of
the information provided by UPR for inclusion in the Registration Statement at
the time it becomes effective and, in the case of the Joint Proxy Statement, at
the date of mailing and at the date of the UPR Stockholders Meeting or the
Anadarko Stockholders Meeting, will contain any untrue statement of a material
fact or omit to state a material fact required to be stated therein or necessary
in order to make the statements therein, in light of the circumstances under
which they were made, not misleading. The Registration Statement and Joint Proxy
Statement, except for such portions thereof that relate only to Anadarko or its
subsidiaries, will each comply as to form in all material respects with the
provisions of the Securities Act and the Exchange Act.

                  4.13 Litigation. There is no Action pending or, to the
knowledge of UPR, threatened against UPR or any executive officer or director of
UPR that, individually or in the aggregate, would reasonably be expected to have
a Material Adverse Effect on UPR or a material adverse effect on the ability of
UPR to consummate the transactions contemplated hereby. UPR is not subject to
any outstanding order, writ, injunction or decree that, individually or in the
aggregate, insofar as can be reasonably foreseen, would have a Material Adverse
Effect on UPR or a material adverse effect on the ability of UPR to consummate
the transactions contemplated hereby.

                  4.14 UPR Employee Benefit Plans

                  (a) For purposes of this Agreement, the following terms have
the definitions given below:

                  "UPR Controlled Group Liability" means any and all liabilities
         (i) under Title IV of ERISA, (ii) under section 302 of ERISA, (iii)
         under sections 412 and 4971 of the Code, (iv) as a result of a failure
         to comply with the continuation coverage requirements of section 601 et
         seq. of ERISA and section 4980B of the Code, and (v) under
         corresponding or similar provisions of foreign laws or regulations,
         other than such liabilities that arise solely out of, or relate solely
         to, the UPR Employee Benefit Plans listed in Section 4.14 of the UPR
         Disclosure Schedule.

                  "UPR Employee Benefit Plan" means any UPR Employee Benefit
         Plan, program, policy, practices, or other arrangement providing
         benefits to any current or former employee, officer or director of UPR
         or any of its subsidiaries or any beneficiary or dependent thereof that
         is sponsored or maintained by UPR or any of its subsidiaries or to
         which UPR or any of its subsidiaries contributes or is obligated to
         contribute, whether or not written, including without limitation any
         employee welfare benefit plan within the meaning of Section 3(1) of
         ERISA, any employee pension benefit plan within the

                                      -25-
<PAGE>   30
         meaning of Section 3(1) of ERISA, any employee pension benefit plan
         within the meaning of Section 3(2) of ERISA (whether or not such plan
         is subject to ERISA) and any bonus, incentive, deferred compensation,
         vacation, stock purchase, stock option, severance, employment, change
         of control or fringe benefit plan, program or agreement.

                  "UPR Employment Agreement" means a contract, offer letter or
         agreement of UPR or any subsidiary with or addressed to any individual
         who is rendering or has rendered services thereto as an employee or
         consultant pursuant to which UPR or any subsidiary has any actual or
         contingent liability or obligation to provide compensation and/or
         benefits in consideration for past, present or future services.

                  "UPR Material Employment Agreement" means an UPR Employment
         Agreement pursuant to which UPR or any subsidiary has or could have any
         obligation to provide compensation and/or benefits (including without
         limitation severance pay or benefits) in an amount or having a value in
         excess of $100,000 per year or $500,000 in the aggregate.

                  "UPR Plan" means any UPR Employee Benefit Plan other than a
         Multiemployer Plan.

                  (a) Section 4.14(a) to the UPR Disclosure Schedule includes a
complete list of all material UPR Employee Benefit Plans and all UPR Material
Employment Agreements.

                  (b) With respect to each UPR Plan, UPR has delivered or made
available to Anadarko a true, correct and complete copy of: (i) each writing
constituting a part of such UPR Plan, including without limitation all plan
documents, employee communications, benefit schedules, trust agreements, and
insurance contracts and other funding vehicles; (ii) the most recent Annual
Report (Form 5500 Series) and accompanying schedule, if any; (iii) the current
summary plan description and any material modifications thereto, if any (in each
case, whether or not required to be furnished under ERISA); (iv) the most recent
annual financial report, if any; (v) the most recent actuarial report, if any;
and (vi) the most recent determination letter from the Internal Revenue Service,
if any. UPR has delivered or made available to Anadarko a true, complete and
correct copy of each UPR Material Employment Agreement. Except as specifically
provided in the foregoing documents delivered or made available to Anadarko,
there are no amendments to any UPR Plan or UPR Material Employment Agreement
that have been adopted or approved.

                  (c) Section 4.14(c) to the UPR Disclosure Schedule identifies
each UPR Plan that is intended to be a "qualified plan" within the meaning of
Section 401(a) of the Code ("UPR Qualified Plans"). The Internal Revenue Service
has issued a favorable determination letter with respect to each UPR Qualified
Plan and the related trust that has not been revoked, or such a letter will be
timely applied for, and, to the knowledge of UPR, there are no circumstances and
no events have occurred that could adversely affect the qualified status of any
UPR Qualified Plan or the related trust. Section 4.14(c) to the UPR Disclosure
Schedule identifies each UPR Plan which is intended to meet the requirements of
Code Section 501(c)(9), and each such plan meets such requirements.


                                      -26-
<PAGE>   31


                  (d) All material contributions required to be made to any UPR
Plan by applicable law or regulation or by any plan document or other
contractual undertaking, and all material premiums due or payable with respect
to insurance policies funding any UPR Plan, for any period through the date
hereof have been timely made or paid in full or, to the extent not required to
be made or paid on or before the date hereof, either (i) have been fully
reflected on the financial statements included in the UPR SEC Documents, or (ii)
items omitted from the UPR SEC Documents could not reasonably be expected to
have a Material Adverse Effect on UPR. Each UPR Employee Benefit Plan that is an
employee welfare benefit plan under Section 3(1) of ERISA is either (i) funded
through an insurance company contract and is not a "welfare benefit fund" with
the meaning of Section 419 of the Code or (ii) unfunded.

                  (e) With respect to each UPR Employee Benefit Plan, UPR and
its subsidiaries have complied, and are now in compliance, in all material
respects, with all provisions of ERISA, the Code and all laws and regulations
applicable to such UPR Employee Benefit Plans and each UPR Employee Benefit Plan
has been administered in all material respects in accordance with its terms.
There is not now, nor, to the knowledge of UPR, do any circumstances currently
exist that could give rise to, any requirement for the posting of security with
respect to a UPR Plan or the imposition of any lien on the assets of UPR or any
of its subsidiaries under ERISA or the Code.

                  (f) With respect to each UPR Plan that is subject to Title IV
or Section 302 of ERISA or Section 412 or 4971 of the Code: (i) there does not
exist any accumulated funding deficiency within the meaning of Section 412 of
the Code or Section 302 of ERISA, whether or not waived; (ii) no reportable
event within the meaning of Section 4043(c) of ERISA for which the 30-day notice
requirement has not been waived has occurred, and the consummation of the
transactions contemplated by this agreement will not result in the occurrence of
any such reportable event; (iii) all premiums to the PBGC have been timely paid
in full; (iv) no liability (other than for premiums to the PBGC) under Title IV
of ERISA has been or is expected to be incurred by UPR or any of its
subsidiaries; and (v) the PBGC has not instituted proceedings to terminate any
such UPR Plan and, to UPR's knowledge, no condition exists that presents a risk
that such proceedings will be instituted or which would constitute grounds under
Section 4042 of ERISA for the termination of, or the appointment of a trustee to
administer, any such UPR Plan.

                  (g)(i) No UPR Employee Benefit Plan is a Multiemployer Plan or
a Multiple Employer Plan; (ii) none of UPR and its subsidiaries nor any of their
respective ERISA Affiliates has, at any time during the last six years,
contributed to or been obligated to contribute to any Multiemployer Plan or
Multiple Employer Plan; and (iii) none of UPR and its subsidiaries nor any of
their respective ERISA Affiliates has incurred any material Withdrawal Liability
that has not been satisfied in full. With respect to each UPR Plan that is a
Multiemployer Plan: (i) if UPR or any of its subsidiaries or any of their
respective ERISA Affiliates were to experience a withdrawal or partial
withdrawal from such plan, no material Withdrawal Liability would be incurred;
and (ii) none of UPR and its subsidiaries, nor any of their respective ERISA
Affiliates has received any notification, nor does UPR have any knowledge that
any such UPR Plan is in reorganization, has been terminated, is insolvent, or
may reasonably be expected to be in reorganization, to be insolvent, or to be
terminated.


                                      -27-
<PAGE>   32

                  (h) There does not now exist, nor, to the knowledge of UPR, do
any circumstances exist that could reasonably be expected to result in, any
material UPR Controlled Group Liability that would be a liability of UPR or any
of its subsidiaries following the Closing. Without limiting the generality of
the foregoing, neither UPR nor, to the knowledge of UPR any of its subsidiaries,
nor any of their respective ERISA Affiliates, has engaged in any transaction
described in Section 4069 or Section 4204 or 4212 of ERISA.

                  (i) Section 4.14(i) to the UPR Disclosure Schedule sets forth
a list of each UPR Employee Benefit Plan or UPR Employment Agreement under which
the execution and delivery of this Agreement or the consummation of the
transactions contemplated hereby could (either alone or in conjunction with any
other event) result in, cause the accelerated vesting, funding or delivery of,
or materially increase the amount or value of, any payment or benefit to any
employee, officer or director of UPR or any of its subsidiaries, or could limit
the right of UPR or any of its subsidiaries to amend, merge, terminate or
receive a reversion of assets from any UPR Employee Benefit Plan or related
trust or any UPR Material Employment Agreement or related trust.

                  (j) None of UPR and its subsidiaries nor, to the knowledge of
UPR, any other person, including any fiduciary, has engaged in any "prohibited
transaction" (as defined in Section 4975 of the Code or Section 406 of ERISA),
which could subject any of the UPR Employee Benefit Plans or their related
trusts, UPR, any of its subsidiaries or any person that UPR or any of its
subsidiaries has an obligation to indemnify, to any material tax or material
penalty imposed under Section 4975 of the Code or Section 502 of ERISA.

                  (k) There are no pending or threatened claims (other than
claims for benefits in the ordinary course), lawsuits or arbitrations which have
been asserted or instituted, and to UPR's knowledge, no set of circumstances
exists which may reasonably give rise to a claim or lawsuit, against the UPR
Plans, any fiduciaries thereof with respect to their duties to the UPR Plans or
the assets of any of the trusts under any of the UPR Plans which could
reasonably be expected to result in any material liability of UPR or any of its
subsidiaries to the PBGC, the Department of Treasury, the Department of Labor,
any Multiemployer Plan, any UPR Plan or any participant in a UPR Plan.

                  (l) UPR, its subsidiaries and each member of their respective
business enterprises have, in all material respects, complied with the Worker
Adjustment and Retraining Notification Act and, in all material respects, all
similar state, local and foreign laws.

                  (m) All UPR Employee Benefit Plans subject to the laws of any
jurisdiction outside of the United States (i) have been maintained in accordance
with all applicable requirements, (ii) if they are intended to qualify for
special tax treatment, meet all requirements for such treatment, and (iii) if
they are intended to be funded and/or book-reserved are funded and/or
book-reserved in all material respects, as appropriate, based upon reasonable
actuarial assumptions.

                  (o) The UPR Employees Thrift Plan (the "ESOP") and the UPR
TRASOP (the "TRASOP") are each "employee stock ownership plans" within the
meaning of Section 4975(e)(7) of the Code. Each loan under which the ESOP is a
borrower (each, a "Loan") meets


                                      -28-
<PAGE>   33

the requirements of Section 4975(d)(3) of the Code. The Securities of UPR that
were acquired with such Loans are in each case pledged as collateral for the
Loan with which they were acquired, except to the extent they have been released
from such pledge and allocated to the accounts of participants in the ESOP in
accordance with the requirements of Treasury Regulations Sections 54.4975-7 and
54.4975-11. The TRASOP has no outstanding indebtedness.

                  4.15 Contracts. All written or oral contracts, agreements,
guarantees, leases and executory commitments other than UPR Plans to which UPR
or its subsidiaries is a party or by which its assets are bound which are
material to UPR (each a "UPR Contract"), are valid and binding obligations of
UPR and, to the knowledge of UPR, the valid and binding obligation of each other
party thereto except such UPR Contracts that if not so valid and binding would
not, individually or in the aggregate, have a Material Adverse Effect on UPR.
Neither UPR nor, to the knowledge of UPR, any other party thereto is in
violation of or in default in respect of, nor has there occurred an event or
condition that with the passage of time or giving of notice (or both) would
constitute a default under or permit the termination of, any such UPR Contract
except such violations or defaults under or terminations that, individually or
in the aggregate, would not have a Material Adverse Effect on UPR. Set forth in
Section 4.15 to the UPR Disclosure Schedule is the amount of the annual premium
currently paid by UPR for its directors' and officers' liability insurance.

                  4.16 Labor Matters. UPR does not have any labor contracts or
collective bargaining agreements with any persons employed by UPR or any persons
otherwise performing services primarily for UPR. There is no labor strike,
dispute or stoppage pending or, to the knowledge of UPR, threatened against UPR,
and UPR has not experienced any labor strike, dispute or stoppage or other
material labor difficulty involving its employees since January 1, 1998. To the
knowledge of UPR, since January 1, 1998, no campaign or other attempt for
recognition has been made by any labor organization or employees with respect to
employees of UPR or any of its subsidiaries.

                  4.17 Undisclosed Liabilities. Except (i) as and to the extent
disclosed or reserved against on the balance sheet of UPR as of December 31,
1999 included in the UPR SEC Documents, or (ii) as incurred after the date
thereof in the ordinary course of business consistent with prior practice and
not prohibited by this Agreement, UPR does not have any liabilities or
obligations of any nature, whether, absolute, accrued, contingent or otherwise
and whether due or to become due, that, individually or in the aggregate, have
had or would reasonably be expected to have a Material Adverse Effect on UPR.

                  4.18 Permits; Compliance. UPR is in possession of all material
franchises, grants, authorizations, licenses, permits, easements, variances,
exemptions, consents, certificates, approvals and orders necessary to own, lease
and operate its properties and to carry on its business as it is now being
conducted (collectively, the "UPR Permits"), and there is no Action pending or,
to the knowledge of UPR, threatened regarding any of the UPR Permits. UPR is not
in conflict with, or in default or violation of any of the UPR Permits, except
for any such conflicts, defaults or violations which, individually or in the
aggregate, could not reasonably be expected to have a Material Adverse Effect on
UPR.



                                      -29-
<PAGE>   34

                  4.19 Environmental Matters. Except as disclosed in the UPR SEC
Documents, (i) the properties, operations and activities of UPR and its
subsidiaries are in compliance with all applicable Environmental Laws and all
past noncompliance of UPR or any UPR subsidiary with any Environmental Laws or
Environmental Permits, has been resolved without any pending, ongoing or future
obligation, cost or liability; (ii) UPR and its subsidiaries and the properties
and operations of UPR and its subsidiaries are not subject to any existing,
pending or, to the knowledge of UPR, threatened Action by or before any court or
Governmental Authority under any Environmental Law; (iii) except as allowed by
Environmental Permits or Environmental Laws, there has been no release of any
hazardous substance, pollutant or contaminant into the environment by UPR or its
subsidiaries or in connection with their properties or operations; and (iv)
except as allowed by Environmental Permits or Environmental Laws, there has been
no exposure of any person or property to any hazardous substance, pollutant or
contaminant in connection with the properties, operations and activities of UPR
and its subsidiaries, in each case, other than those matters that, individually
or in the aggregate, would not reasonably be expected to have a Material Adverse
Effect on UPR.

                  4.20 Opinion of Financial Advisor. UPR has received the
written opinion of Goldman, Sachs & Co., to the effect that, as of the date of
this Agreement, the Exchange Ratio is fair to the UPR Stockholders from a
financial point of view. UPR has heretofore provided copies of such opinions to
Anadarko and such opinions have not been withdrawn or revoked or modified.

                  4.21 Board Recommendation; Required Vote. The Board of
Directors of UPR, at a meeting duly called and held, has by unanimous vote of
those directors present (i) determined that this Agreement and the transactions
contemplated hereby, including the Merger, and the UPR Stock Option Agreement
and the transactions contemplated thereby, taken together, are fair to and in
the best interests of the UPR Stockholders, and (ii) resolved to recommend that
the holders of the shares of UPR Common Stock approve this Agreement and the
transactions contemplated herein, including the Merger (the "UPR Board
Recommendation"). The affirmative vote of holders of a majority of the
outstanding shares of UPR Common Stock to approve the Merger is the only vote of
the holders of any class or series of UPR Common Stock necessary to adopt the
Agreement and approve the transactions contemplated hereby.

                  4.22 State Takeover Laws; Rights Agreement. Prior to the
execution of this Agreement, the Board of Directors of UPR has taken all action
necessary to exempt under or make not subject to any state takeover law or state
law that purports to limit or restrict business combinations or the ability to
acquire or vote shares: (i) the execution of this Agreement, and the UPR Stock
Option Agreement, (ii) the Merger and (iii) the transactions contemplated hereby
and by the UPR Stock Option Agreement. The Amended and Restated Rights
Agreement, dated as of December 1, 1998 (the "UPR Rights Agreement"), between
UPR and Harris Trust and Savings Bank, as Rights Agent, has been amended so that
Anadarko and Subcorp are each exempt from the definition of "Acquiring Person"
contained in the UPR Rights Agreement, no "Stock Acquisition Date" or
"Distribution Date" or "Triggering Event" (as such terms are defined in the UPR
Rights Agreement) will occur as a result of the execution of this Agreement or
the UPR Stock Option Agreement or the consummation of the Merger pursuant to
this Agreement or the acquisition or transfer of shares of UPR Common Stock by
Anadarko pursuant to the UPR Stock Option Agreement and the UPR Rights Agreement
will expire immediately


                                      -30-
<PAGE>   35

prior to the Effective Time, and the UPR Rights Agreement, as so amended, has
not been further amended or modified. Copies of all such amendments to the UPR
Rights Agreement have been previously provided to Anadarko.

                                   ARTICLE V.

                            COVENANTS OF THE PARTIES

                  The parties hereto agree that:

                  5.1 Mutual Covenants.

                  (a) HSR Act Filings; Reasonable Efforts; Notification.

               (i) Each of Anadarko and UPR shall (A) make or cause to be made
         the filings required of such party or any of its subsidiaries or
         affiliates under the HSR Act with respect to the transactions
         contemplated hereby as promptly as practicable and in any event within
         fifteen business days after the date of this Agreement, (B) comply at
         the earliest practicable date with any request under the HSR Act for
         additional information, documents, or other materials received by such
         party or any of its subsidiaries from the Federal Trade Commission or
         the Department of Justice or any other Governmental Authority in
         respect of such filings or such transactions, and (C) cooperate with
         the other party in connection with any such filing (including, with
         respect to the party making a filing, providing copies of all such
         documents to the non-filing party and its advisors prior to filing
         (other than documents containing confidential business information that
         shall be shared only with outside counsel to the non-filing party)).
         Each party shall use its reasonable efforts to furnish to each other
         all information required for any application or other filing to be made
         pursuant to any Applicable Law in connection with the Merger and the
         other transactions contemplated by this Agreement. Each party shall
         promptly inform the other party of any substantive communication with,
         and any proposed understanding, undertaking, or agreement with, any
         Governmental Authority regarding any such filings or any such
         transaction. The parties hereto will consult and cooperate with 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 other Antitrust Laws.

               (ii) Each of Anadarko and UPR shall use its reasonable efforts to
         resolve such objections, if any, as may be asserted by any Governmental
         Authority with respect to the transaction contemplated by this
         Agreement under the HSR Act, the Sherman Act, as amended, the Clayton
         Act, as amended, the Federal Trade Commission Act, as amended, and any
         other federal, state or foreign statutes, rules, regulations, orders,
         decrees, administrative or judicial doctrines or other laws that are
         designed to prohibit, restrict or regulate actions having the purpose
         or effect of monopolization or restraint of trade (collectively,
         "Antitrust Laws"). In connection therewith, if any administrative or
         judicial action or proceeding is instituted (or threatened to be
         instituted) challenging any transaction contemplated by this Agreement
         as violative of any Antitrust Law, each of


                                      -31-
<PAGE>   36


         Anadarko and UPR shall cooperate and use its reasonable efforts
         vigorously to contest and resist any such action or proceeding,
         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 is in effect and that prohibits, prevents, or restricts
         consummation of the Merger or any other transactions contemplated by
         this Agreement. Notwithstanding the foregoing or any other provision of
         this Agreement, nothing in this Section 5.1(a) shall limit a party's
         right to terminate this Agreement pursuant to Article VII, so long as
         such party has up to then complied in all material respects with its
         obligations under this Section 5.1(a). Each of Anadarko and UPR shall
         use all reasonable efforts to take such action as may be required to
         cause the expiration of the notice periods under the HSR Act or other
         Antitrust Laws with respect to such transactions as promptly as
         possible after the execution of this Agreement.

               (iii) Each of the parties hereto agrees to use its reasonable
         efforts to take, or cause to be taken, all actions, and to do, or cause
         to be done, and to assist and cooperate with the other parties hereto
         in doing, all things necessary, proper or advisable to consummate and
         make effective, in the most expeditious manner practicable, the Merger
         and the other transactions contemplated by this Agreement, including
         (A) the obtaining of all other necessary actions or nonactions,
         waivers, consents, licenses, permits, authorizations, orders and
         approvals from Governmental Authorities and the making of all other
         necessary registrations and filings (including other filings with
         Governmental Authorities, if any), (B) the obtaining of all consents,
         approvals or waivers from third parties related to or required in
         connection with the Merger that are necessary to consummate the Merger
         and the transactions contemplated by this Agreement or required to
         prevent a Material Adverse Effect on Anadarko or UPR from occurring
         prior to or after the Effective Time, (C) the preparation of the Joint
         Proxy Statement, the Prospectus and the Registration Statement, and (D)
         the execution and delivery of any additional instruments necessary to
         consummate the transaction contemplated by, and to fully carry out the
         purposes of, this Agreement.

               (iv) Notwithstanding anything to the contrary in this Agreement,
         (A) neither Anadarko nor any of its subsidiaries shall be required to
         hold separate (including by trust or otherwise) or to divest any of
         their respective businesses or assets, or to take or agree to take any
         action or agree to any limitation that could reasonably be expected to
         have a Material Adverse Effect on Anadarko and its subsidiaries taken
         as a whole or a material adverse effect on the business, assets,
         liabilities, results of operations, financial condition or prospects of
         Anadarko combined with the Surviving Corporation after the Effective
         Time, (B) prior to the Effective Time, neither UPR nor its subsidiaries
         shall be required to hold separate (including by trust or otherwise) or
         to divest any of their respective businesses or assets, or to take or
         agree to take any other action or agree to any limitation that could
         reasonably be expected to have a Material Adverse Effect on UPR and its
         subsidiaries taken as a whole, (C) neither Anadarko nor UPR nor their
         respective subsidiaries shall be required to take any action that could
         reasonably be expected to substantially impair the overall benefits
         expected, as of the date hereof, to be realized from consummation of
         the Merger and (D) neither Anadarko nor UPR shall be required


                                      -32-
<PAGE>   37

         to waive any of the conditions to the Merger set forth in Article VI as
         they apply to such party.

                  (b) Tax-Free Treatment. Each of the parties shall use its
reasonable efforts to cause the Merger to constitute a "reorganization" under
Section 368(a) of the Code and to cooperate with one another in obtaining an
opinion to UPR from Morgan Lewis & Bockius LLP, counsel to UPR, as provided for
in Section 6.1(g), including, but not limited to, making such filings and
maintaining such records as are required by Treasury Regulation Section 1.368-3.

                  (c) Public Announcements. The initial press release concerning
the Merger and the transactions contemplated hereby shall be a joint press
release. Unless otherwise required by Applicable Laws or requirements of the
NYSE (and, in that event, only if time does not permit), at all times prior to
the earlier of the Effective Time or termination of this Agreement pursuant to
Section 7.1, Anadarko and UPR shall consult with each other before issuing any
press release with respect to the Merger and the transactions contemplated
thereby and shall not issue any such press release prior to such consultation.

                  (d) Farmouts. Except as set forth below, neither Anadarko nor
UPR shall enter into any farmouts except farmouts in accordance with the
guidelines for farmouts or similar transactions jointly developed by their
respective Chief Executive Officers. Prior to the time such guidelines are
established, neither Anadarko nor UPR shall enter into any farmouts without
first consulting with the other party.

                  5.2 Covenants of Anadarko.

                  (a) Anadarko Stockholders Meeting. Anadarko shall take all
action in accordance with the federal securities laws, the Delaware General
Corporation Law, the Anadarko Certificate and the Anadarko By-laws, necessary to
duly call, give notice of, convene and hold a special meeting of Anadarko
Stockholders (the "Anadarko Stockholders Meeting") to be held on the earliest
practical date determined in consultation with UPR, and to obtain the consent
and approval of Anadarko Stockholders with respect to the Share Issuance, the
Anadarko Board Amendment and the transactions contemplated hereby. Anadarko
shall take all lawful action to solicit the approval of the Share Issuance and
the Anadarko Board Amendment by the Anadarko Stockholders and the Board of
Directors of Anadarko shall recommend approval of the Share Issuance and the
Anadarko Board Amendment by the Anadarko Stockholders (to the extent not
previously withdrawn pursuant to Section 5.2(d)).

                  (b) Preparation of Registration Statement. Anadarko shall, as
soon as is reasonably practicable, prepare the Joint Proxy Statement for filing
with the Commission and shall file the Joint Proxy Statement. Consistent with
the timing for the Anadarko Stockholders Meeting and the UPR Stockholders
Meeting as determined by Anadarko after consultation with UPR, Anadarko shall
prepare and file the Registration Statement with the Commission as soon as is
reasonably practicable following clearance of the Joint Proxy Statement by the
Commission and shall use its reasonable efforts to have the Registration
Statement declared effective by the Commission as promptly as practicable and to
maintain the effectiveness of the Registration Statement through the Effective
Time. If, at any time prior to the Effective Time, Anadarko shall obtain
knowledge of any information pertaining to Anadarko contained in or omitted from


                                      -33-
<PAGE>   38


the Registration Statement that would require an amendment or supplement to the
Registration Statement or the Joint Proxy Statement, Anadarko will so advise UPR
in writing and will promptly take such action as shall be required to amend or
supplement the Registration Statement and/or the Joint Proxy Statement. Anadarko
shall promptly furnish to UPR all information concerning it as may be required
for supplementing the Joint Proxy Statement. Anadarko shall cooperate with UPR
in the preparation of the Joint Proxy Statement in a timely fashion and shall
use its reasonable efforts to assist UPR in clearing the Joint Proxy Statement
with the Staff of the Commission. Consistent with the timing of the Anadarko
Stockholders Meeting and the UPR Stockholder Meeting, Anadarko shall use all
reasonable efforts to mail at the earliest practicable date to Anadarko
Stockholders the Joint Proxy Statement, which Joint Proxy Statement shall
include all information required under Applicable Law to be furnished to
Anadarko Stockholders in connection with the Share Issuance and shall include
the Anadarko Board Recommendation to the extent not previously withdrawn in
compliance with Section 5.2(d) and the written opinion of the Anadarko Financial
Advisor described in Section 3.21. Anadarko shall also take such other
reasonable actions (other than qualifying to do business in any jurisdiction in
which it is not so qualified) required to be taken under any applicable state
securities laws in connection with the issuance of Anadarko Common Shares in the
Merger. No filing of, or amendment or supplement to, the Registration Statement
or to the Joint Proxy Statement will be made by Anadarko without providing UPR
the opportunity to review and comment thereon. Anadarko will advise UPR,
promptly after it receives notice thereof, of the time when the Registration
Statement has become effective or any supplement or amendment has been filed,
the issuance of any stop order, the suspension of the qualification of Anadarko
Common Shares issuable in connection with the Merger for offering or sale in any
jurisdiction, or any request by the Commission for amendment of the Joint Proxy
Statement or the Registration Statement or comments thereon and responses
thereto or requests by the Commission for additional information.

                  (c) Conduct of Anadarko's Operations. Anadarko shall conduct
its operations in the ordinary course except as expressly contemplated by this
Agreement and the transactions contemplated hereby and shall use all reasonable
efforts to maintain and preserve its business organization and its material
rights and franchises and to retain the services of its officers and key
employees and maintain relationships with customers, suppliers, lessees, joint
venture partners, licensees and other third parties, and to maintain all of its
operating assets in their current condition (normal wear and tear excepted), to
the end that their goodwill and ongoing business shall not be impaired in any
material respect. Without limiting the generality of the foregoing, during the
period from the date of this Agreement to the Effective Time, Anadarko shall
not, except as otherwise expressly contemplated by this Agreement and the
transactions contemplated hereby or as set forth in Section 5.2(c) to the
Anadarko Disclosure Schedule, without the prior consent of the Chief Executive
Officer of UPR (which consent shall not be unreasonably withheld):

                  (i) do or effect any of the following actions with respect to
         its securities: (A) adjust, split, combine or reclassify its capital
         stock, (B) make, declare or pay any dividend (other than regular
         quarterly dividends on Anadarko Common Shares of $0.05 per share with
         record and payment dates consistent with past practice) or distribution
         on, or, directly or indirectly, redeem, purchase or otherwise acquire,
         any shares of its capital stock or any securities or obligations
         convertible into or exchangeable for any shares of


                                      -34-
<PAGE>   39

         its capital stock, (C) grant any person any right or option to acquire
         any shares of its capital stock, (D) issue, deliver or sell or agree to
         issue, deliver or sell any additional shares of its capital stock or
         any securities or obligations convertible into or exchangeable or
         exercisable for any shares of its capital stock or such securities
         (except pursuant to the exercise of Anadarko Options that are
         outstanding as of the date hereof), or (E) enter into any agreement,
         understanding or arrangement with respect to the sale, voting,
         registration or repurchase of its capital stock;

                  (ii) directly or indirectly sell, transfer, lease, pledge,
         mortgage, encumber or otherwise dispose of any of its property or
         assets other than: (A) dispositions of oil, gas and other minerals in
         the ordinary course of business, consistent with past practice, (B)
         pledges, mortgages or encumbrances in the ordinary course of business,
         consistent with past practice, or (C) sales, leases or dispositions
         with a total value not to exceed $50 million individually or in the
         aggregate, it being understood that sub-clauses (A), (B) and (C) do not
         apply to farmouts;

                  (iii) except to the extent contemplated by this Agreement,
         make or propose any changes in the Anadarko Certificate or the Anadarko
         By-laws;

                  (iv) merge or consolidate with any other person (other than
         mergers among wholly owned subsidiaries of Anadarko and mergers between
         Anadarko and its wholly owned subsidiaries);

                  (v) acquire a material amount of assets or capital stock of
         any other person (other than acquisition of assets in the ordinary
         course of business, consistent with past practice with a total value
         not to exceed $25 million individually, or in the aggregate);

                  (vi) amend or modify, or propose to amend or modify, the
         Anadarko Rights Agreement, as amended as of the date hereof;

                  (vii) incur, create, assume or otherwise become liable for any
         indebtedness for borrowed money or assume, guarantee, endorse or
         otherwise as an accommodation become responsible or liable for the
         obligations of any other individual, corporation or other entity, other
         than in the ordinary course of business, consistent with past practice,
         which in no event shall exceed $200 million in the aggregate;

                  (viii) except as may be required by Applicable Law or by the
         terms of Anadarko Plans or Anadarko Employment Agreements in effect as
         of the date hereof, enter into or modify any employment, severance,
         termination or similar agreements or arrangements with, or grant any
         bonuses, salary increases, severance or termination pay to, any
         officer, director, consultant or employee, or otherwise increase, fund
         or accelerate the funding of any compensation or benefits provided to
         any officer, director, consultant or employee, contribute any assets to
         any grantor trust, or grant, reprice, or accelerate the exercise or
         payment of any Anadarko Options or other equity-based awards other than
         any payment of bonuses or increases in salary that are both consistent
         with the past practice of Anadarko and not material;


                                      -35-
<PAGE>   40

                  (ix) enter into, adopt or amend any Anadarko Employee Benefit
         Plan or Anadarko Employment Agreement, except as may be required by
         Applicable Law, other than amendments in the ordinary course,
         consistent with past practice that do not increase, reduce or
         accelerate benefits, make payout options more favorable to
         participants, or otherwise result in any increased cost to Anadarko;

                  (x) take any action that could give rise to a right to
         severance benefits pursuant to any change in control agreement;

                  (xi) change any method or principle of accounting in a manner
         that is inconsistent with past practice except to the extent required
         by United States generally accepted accounting principles as advised by
         Anadarko's regular independent accountants;

                  (xii) settle any Actions, whether now pending or hereafter
         made or brought involving, individually an amount in excess of $1
         million, or in the aggregate, an amount in excess of $20 million;

                  (xiii) modify, amend or terminate, or waive, release or assign
         any material rights or claims with respect to any confidentiality
         agreement to which Anadarko is a party;

                  (xiv) enter into any confidentiality agreements or
         arrangements other than in the ordinary course of business consistent
         with past practice (other than as permitted, in each case, by Section
         5.2(d));

                  (xv) write up, write down or write off the book value of any
         assets, individually or in the aggregate, in excess of $5 million
         except for depreciation and amortization and provisions (e.g.,
         surrendered leases) in accordance with generally accepted accounting
         principles consistently applied or as otherwise required by generally
         accepted accounting principles;

                  (xvi) incur or commit to any capital expenditures not included
         in the dollar limits of the Anadarko Capital Budget as in effect on the
         date of this Agreement (a copy of which included in Section 5.2(c) to
         the Anadarko Disclosure Schedule);

                  (xvii) make any payments in respect of policies of directors'
         and officers' liability insurance (premiums or otherwise) other than
         premiums paid in respect of its current policies and renewals thereof
         at the same policy limits;

                  (xviii) take any action to exempt or make not subject to the
         provisions of any state takeover law or state law that purports to
         limit or restrict business combinations or the ability to acquire or
         vote shares, any person or entity (other than UPR or its subsidiaries)
         or any action taken thereby, which person, entity or action would have
         otherwise been subject to the restrictive provisions thereof and not
         exempt therefrom;

                  (xix) take any action that would likely result in the
         representations and warranties set forth in Article III becoming false
         or inaccurate in any material respect;


                                      -36-
<PAGE>   41

                  (xx) enter into or carry out any other transaction other than
         in the ordinary and usual course of business;

                  (xxi) permit or cause any subsidiary to do any of the
         foregoing or agree or commit to do any of the foregoing;

                  (xxii) except as otherwise required by law, make any material
         Tax election, settle or compromise any material Tax claim, file any Tax
         Return (other than in a manner consistent with past practice) or change
         any method of Tax accounting; or

                  (xxiii) agree in writing or otherwise to take any of the
         foregoing actions.


                  (d) No Solicitation. Anadarko agrees that, during the term of
this Agreement, it shall not, and shall not authorize or permit any of its
subsidiaries or any of its or its subsidiaries' directors, officers, employees,
agents or representatives, directly or indirectly, to solicit, initiate,
encourage or facilitate, or furnish or disclose non-public information in
furtherance of, any inquiries or the making of any proposal with respect to any
recapitalization, merger, consolidation or other business combination involving
Anadarko, or any acquisition of 15% or more of the capital stock (other than
upon exercise of Anadarko Options that are outstanding as of the date hereof) or
30% or more of the assets of Anadarko and its subsidiaries, taken as a whole, in
a single transaction or a series of related transactions, or any combination of
the foregoing (an "Anadarko Competing Transaction"), or negotiate, explore or
otherwise engage in discussions with any person (other than UPR, Subcorp or
their respective directors, officers, employees, agents and representatives)
with respect to any Anadarko Competing Transaction or enter into any agreement,
arrangement or understanding requiring it to abandon, terminate or fail to
consummate the Merger or any other transactions contemplated by this Agreement;
provided that, at any time prior to the approval of the Share Issuance by the
Anadarko Stockholders, Anadarko may furnish information to, and engage in
discussions with, any party who delivers a written proposal for an Anadarko
Competing Transaction which was not solicited or encouraged after the date of
this Agreement in violation of this Agreement if and so long as the Board of
Directors of Anadarko determines in good faith by resolution duly adopted after
consultation with its outside counsel (who may be its regularly engaged outside
counsel) that the failure to take such action would reasonably be expected to
constitute a breach of its fiduciary duties under Applicable Law and determines
that such a proposal is, after consulting with the Anadarko Financial Advisor,
more favorable to Anadarko Stockholders from a financial point of view than the
transactions contemplated by this Agreement (including any adjustment to the
terms and conditions proposed by UPR in response to such Anadarko Competing
Transaction) (an "Anadarko Superior Proposal"); provided, further, that prior to
furnishing information to, or engaging in discussions with, any party pursuant
to the foregoing proviso, Anadarko shall have received an executed agreement
from such party in the same form as the Confidentiality Agreement (other than
Section 8 thereof which shall be waived for UPR under the Confidentiality
Agreement upon the execution of such agreement). Anadarko will immediately cease
all existing activities, discussions and negotiations with any parties conducted
heretofore with respect to any proposal for an Anadarko Competing Transaction
and request the return of all confidential information regarding Anadarko
provided to any such parties prior to the date hereof pursuant to the terms of
any confidentiality agreements or otherwise. In the event that prior to the
approval of the Share Issuance by the Anadarko Stockholders, the Board of
Directors


                                      -37-
<PAGE>   42

of Anadarko receives an Anadarko Superior Proposal that was not solicited or
encouraged after the date of this Agreement in violation of this Agreement, and
the Board of Directors of Anadarko determines in good faith by resolution duly
adopted after consultation with its outside counsel (who may be its regularly
engaged outside counsel) that the failure to take such action would reasonably
be expected to constitute a breach of its fiduciary duties under Applicable Law,
the Board of Directors of Anadarko may (subject to this and the following
sentences) withdraw, modify or change, in a manner adverse to UPR, the Anadarko
Board Recommendation and/or comply with Rule 14e-2 promulgated under the
Exchange Act with respect to an Anadarko Competing Transaction, provided that it
gives UPR three business days' prior written notice of its intention to do so
(provided that the foregoing shall in no way limit or otherwise affect UPR's
right to terminate this Agreement pursuant to Section 7.4(b)). Any such
withdrawal, modification or change of the Anadarko Board Recommendation shall
not change the approval of the Board of Directors of Anadarko for purposes of
causing any state takeover statute or other state law to be inapplicable to the
transactions contemplated hereby, including the Merger or the Anadarko Stock
Option Agreement or change the obligation of Anadarko to present the Share
Issuance for approval at a duly called Anadarko Stockholders Meeting on the
earliest practicable date determined in consultation with UPR. From and after
the execution of this Agreement, Anadarko shall promptly (but in any event
within one calendar day) advise UPR in writing of the receipt, directly or
indirectly, of any inquiries, discussions, negotiations, or proposals relating
to an Anadarko Competing Transaction (including the specific terms thereof and
the identity of the other party or parties involved) and promptly furnish to UPR
a copy of any such written proposal in addition to any information provided to
or by any third party relating thereto. In addition, Anadarko shall promptly
(but in any event within one calendar day) advise UPR, in writing, if the Board
of Directors of Anadarko shall make any determination as to any Anadarko
Competing Transaction as contemplated by the proviso to the first sentence of
this Section 5.2(d).

                  (e) Indemnification; Directors' and Officers' Insurance.

                  (i) From and after the Effective Time, Anadarko shall cause
         the Surviving Corporation to indemnify and hold harmless (including
         providing funding therefor) the present and former officers and
         directors of UPR in respect of acts or omissions occurring prior to the
         Effective Time to the extent provided under the UPR Articles or the UPR
         Bylaws, and

                  (ii) Anadarko shall use all reasonable best efforts to cause
         the Surviving Corporation or Anadarko to obtain and maintain in effect
         for a period of six years after the Effective Time policies of
         directors' and officers' liability insurance at no cost to the
         beneficiaries thereof with respect to acts or omissions occurring prior
         to the Effective Time with substantially the same coverage and
         containing substantially similar terms and conditions as existing
         policies; provided, however, that neither the Surviving Corporation nor
         Anadarko shall be required to pay an aggregate premium for such
         insurance coverage in excess of 200% of the amount set forth in Section
         4.15 to the UPR Disclosure Schedule; provided, further, that if the
         annual premiums of such insurance coverage exceed such amount, Anadarko
         shall be obligated to obtain a policy with the best coverage available,
         in the reasonable judgment of the Board of Directors of Anadarko, for a
         cost not exceeding such amount.


                                      -38-
<PAGE>   43


                  (f) NYSE Listing. Anadarko shall use its reasonable efforts to
cause the Anadarko Common Shares issuable pursuant to the Merger (including
pursuant to Anadarko Exchange Options) to be approved for listing on the NYSE,
subject to official notice of issuance, prior to the Effective Time.

                  (g) Access. Anadarko shall permit representatives of UPR to
have access at all reasonable times to Anadarko's premises, properties, books,
records, contracts, documents, customers and suppliers. Information obtained by
UPR pursuant to this Section 5.2 shall be subject to the provisions of the
confidentiality agreement between Anadarko and UPR dated February 22, 2000 (the
"Confidentiality Agreement"), which agreement remains in full force and effect.
No investigation conducted pursuant to this Section 5.2 shall affect or be
deemed to modify any representation or warranty made in this Agreement.

                  (h) Board of Directors of Anadarko. At the Anadarko
Stockholders Meeting, Anadarko shall take all action necessary in accordance
with Applicable Law, the Anadarko Certificate and the Anadarko By-Laws to have
the Anadarko Stockholders consider and vote upon an amendment to the Anadarko
Certificate to increase the size of the Board of Directors of Anadarko to at
least 13 members (the "Anadarko Board Amendment"). In the event that the
Anadarko Board Amendment is approved, then the Board of Directors of Anadarko
shall take all action necessary immediately following the Effective Time to
elect as directors of Anadarko Mr. CEO, and four other independent directors who
are currently members of the Board of Directors of UPR as may be mutually agreed
by the Chief Executive Officer of Anadarko and the Chief Executive Officer of
UPR prior to the Effective Time. In the event that the Anadarko Stockholders do
not approve the Anadarko Board Amendment, the Board of Directors of Anadarko
shall take all action necessary immediately following the Effective Time to
elect as directors of Anadarko Mr. George Lindahl III, and two other independent
directors who are currently members of the Board of Directors of UPR as may be
mutually agreed by the Chief Executive Officer of Anadarko and the Chief
Executive Officer of UPR prior to the Effective Time. The former UPR directors
elected as directors of Anadarko shall be appointed among Classes I, II and III
with a minimum of one director per Class.

                  (i) Subsequent Financial Statements. Anadarko shall consult
with UPR prior to making publicly available its financial results for any period
after the date of this Agreement and prior to filing any Anadarko SEC Documents
after the date of this Agreement.

                  (j) Employees and Employee Benefits.

(A)      From and after the Effective Time, the Surviving Corporation shall
         assume and honor all UPR Plans and UPR Employment Agreements in
         accordance with their terms as in effect immediately before the
         Effective Time, subject to any amendment or termination thereof that
         may be permitted by such terms. Until at least the first anniversary of
         the Effective Time (the "Benefits Transition Period"), Anadarko shall
         provide, or shall cause to be provided, to individuals who are,
         immediately before the Effective Time, employees of UPR and its
         subsidiaries who are not subject to collective bargaining (the "UPR
         Employees"), employee benefits, other than equity-based benefits, that
         are, in the aggregate, comparable to the benefits, other than
         equity-based benefits, provided to UPR Employees under the UPR Plans
         immediately before the Effective Time (the "UPR


                                      -39-
<PAGE>   44

         Benefits"). Following the end of the Benefits Transition Period, or, at
         its discretion, prior to the end of the Benefits Transition Period, in
         lieu of the UPR Benefits, Anadarko shall provide, or cause to be
         provided, to UPR employees, employee benefits that are in the aggregate
         comparable to those provided, to similarly situated employees of
         Anadarko. The foregoing shall not be construed to prevent the
         termination of employment of any UPR Employee or the amendment or
         termination of any particular UPR Employee Benefit Plan to the extent
         permitted by its terms as in effect immediately before the Effective
         Time.

(B)      For all purposes under the employee benefit plans of Anadarko and its
         affiliates (including the Surviving Corporation) providing benefits to
         any UPR Employees after the Effective Time (the "New Plans"), each UPR
         Employee shall be credited with his or her years of service with UPR
         and its subsidiaries before the Effective Time, to the same extent as
         such UPR Employee was entitled, before the Effective Time, to credit
         for such service under any similar UPR Employee Benefit Plans, except
         for purposes of benefit accrual under defined benefit pension plans and
         except as would result in a duplication of benefits. In addition, and
         without limiting the generality of the foregoing: (i) each UPR Employee
         shall be immediately eligible to participate, without any waiting time,
         in any and all New Plans to the extent coverage under such New Plan
         replaces coverage under a comparable UPR Employee Benefit Plan in which
         such UPR Employee participated immediately before the Effective Time
         (such plans, collectively, the "Old Plans"); and (ii) for purposes of
         each New Plan providing medical, dental, pharmaceutical and/or vision
         benefits to any UPR Employee, Anadarko shall cause all pre-existing
         condition exclusions and actively-at-work requirements of such New Plan
         to be waived for such employee and his or her covered dependents, and
         Anadarko shall cause any eligible expenses incurred by such employee
         and his or her covered dependents during the portion of the plan year
         of the Old Plan ending on the date such employee's participation in the
         corresponding New Plan begins to be taken into account under such New
         Plan for purposes of satisfying all deductible, coinsurance and maximum
         out-of-pocket requirements applicable to such employee and his or her
         covered dependents for the applicable plan year as if such amounts had
         been paid in accordance with such New Plan.

(C)      Without limiting the generality of the foregoing, following the
         Effective Time, and until such time as Anadarko shall otherwise
         determine, the ESOP shall continue in effect holding the Anadarko
         Common Shares that it receives in the Merger, and the Loans shall
         continue to remain outstanding and be repaid in accordance with their
         terms.

                  5.3 Covenants of UPR.

                  (a) UPR Stockholders Meeting. UPR shall take all action in
accordance with the federal securities laws, the UBCA and the UPR Articles and
the UPR Bylaws necessary to duly call, give notice of, convene and hold a
special meeting of UPR Stockholders (the "UPR Stockholders Meeting") to be held
on the earliest practicable date determined in consultation with Anadarko to
consider and vote upon approval of the Merger, this Agreement and the
transactions contemplated hereby. UPR shall take all lawful actions to solicit
the approval of the Merger, this Agreement and the transactions contemplated
hereby, by the UPR Stockholders, and the Board of Directors of UPR shall
recommend approval of the Merger, this Agreement and the


                                      -40-
<PAGE>   45

transactions contemplated hereby by the UPR Stockholders (to the extent not
previously withdrawn pursuant to Section 5.3(d)).

                  (b) Information for the Registration Statement and Preparation
of Joint Proxy Statement. UPR shall promptly furnish Anadarko with all
information concerning it as may be required for inclusion in the Joint Proxy
Statement and the Registration Statement. UPR shall cooperate with Anadarko in
the preparation of the Joint Proxy Statement and the Registration Statement in a
timely fashion and shall use all reasonable efforts to assist Anadarko in having
the Registration Statement declared effective by the Commission as promptly as
practicable consistent with the timing for the Anadarko Stockholders Meeting and
the UPR Stockholders Meeting as determined by Anadarko after consultation with
UPR. If, at any time prior to the Effective Time, UPR obtains knowledge of any
information pertaining to UPR that would require any amendment or supplement to
the Registration Statement or the Joint Proxy Statement, UPR shall so advise
Anadarko and shall promptly furnish Anadarko with all information as shall be
required for such amendment or supplement and shall promptly amend or supplement
the Registration Statement and/or Joint Proxy Statement. UPR shall use all
reasonable efforts to cooperate with Anadarko in the preparation and filing of
the Joint Proxy Statement with the Commission. Consistent with the timing for
the Anadarko Stockholders Meeting and the UPR Stockholders Meeting as determined
by Anadarko after consultation with UPR, UPR shall use all reasonable efforts to
mail at the earliest practicable date to UPR Stockholders the Joint Proxy
Statement, which shall include all information required under Applicable Law to
be furnished to UPR Stockholders in connection with the Merger and the
transactions contemplated thereby and shall include the UPR Board Recommendation
to the extent not previously withdrawn in compliance with Section 5.3(d) and the
written opinion of Goldman, Sachs & Co. described in Section 4.21.

                  (c) Conduct of UPR's Operations. UPR shall conduct its
operations in the ordinary course except as expressly contemplated by this
Agreement and the transactions contemplated hereby and shall use all reasonable
efforts to maintain and preserve its business organization and its material
rights and franchises and to retain the services of its officers and key
employees and maintain relationships with customers, suppliers, lessees, joint
venture partners, licensees and other third parties, and to maintain all of its
operating assets in their current condition (normal wear and tear excepted), to
the end that their goodwill and ongoing business shall not be impaired in any
material respect. Without limiting the generality of the foregoing, during the
period from the date of this Agreement to the Effective Time, UPR shall not,
except as otherwise expressly contemplated by this Agreement and the
transactions contemplated hereby or as set forth in Section 5.3(c) to the UPR
Disclosure Schedule, without the prior consent of the Chief Executive Officer of
Anadarko (which consent shall not be unreasonably withheld):

                  (i) do or effect any of the following actions with respect to
         its securities: (A) adjust, split, combine or reclassify its capital
         stock, (B) make, declare or pay any dividend (other than regular
         quarterly dividends on UPR Common Stock of $0.05 per share with record
         and payment dates consistent with past practice) or distribution on,
         or, directly or indirectly, redeem, purchase or otherwise acquire, any
         shares of its capital stock or any securities or obligations
         convertible into or exchangeable for any shares of its capital stock,
         (C) grant any person any right or option to acquire any shares of its


                                      -41-
<PAGE>   46


         capital stock, (D) issue, deliver or sell or agree to issue, deliver or
         sell any additional shares of its capital stock or any securities or
         obligations convertible into or exchangeable or exercisable for any
         shares of its capital stock or such securities (except pursuant to the
         exercise of UPR Options that are outstanding as of the date hereof), or
         (E) enter into any agreement, understanding or arrangement with respect
         to the sale, voting, registration or repurchase of its capital stock;

                  (ii) directly or indirectly sell, transfer, lease, pledge,
         mortgage, encumber or otherwise dispose of any of its property or
         assets other than: (A) dispositions of oil, gas and other minerals in
         the ordinary course of business, consistent with past practice, (B)
         pledges, mortgages, encumbrances in the ordinary course of business
         consistent with past practice, or (c) sales, leases or dispositions
         with a total value not to exceed $50 million individually or in the
         aggregate, it being understood that sub-clauses (A), (B) and (C) do not
         apply to farmouts;

                  (iii) make or propose any changes in the UPR Articles or the
         UPR Bylaws;

                  (iv) merge or consolidate with any other person (other than
         mergers among wholly owned subsidiaries of UPR and mergers between UPR
         and its wholly owned subsidiaries);

                  (v) acquire a material amount of assets or capital stock of
         any other person; (other than acquisitions of assets in the ordinary
         course of business, consistent with past practice with a total value
         not to exceed $25 million individually or in the aggregate);

                  (vi) amend or modify, or propose to amend or modify, the UPR
         Rights Agreement, as amended as of the date hereof;

                  (vii) incur, create, assume or otherwise become liable for any
         indebtedness for borrowed money or assume, guarantee, endorse or
         otherwise as an accommodation become responsible or liable for the
         obligations of any other individual, corporation or other entity, other
         than in the ordinary course of business, consistent with past practice,
         which in no event shall exceed $200 million in the aggregate;

                  (viii) except as may be required by Applicable Law or by the
         terms of UPR Plans or UPR Employment Agreements that are in effect as
         of the date hereof, enter into or modify any employment, severance,
         termination or similar agreements or arrangements with, or grant any
         bonuses, salary increases, severance or termination pay to, any
         officer, director, consultant or employee, or otherwise increase, fund
         or accelerate the funding of any compensation or benefits provided to
         any officer, director, consultant or employee, contribute any assets to
         any grantor trust, or grant, reprice, or accelerate the exercise or
         payment of any UPR Options or other equity-based awards, other than any
         payment of bonuses or increases in salary that are both consistent with
         the past practice of UPR and are not material;

                  (ix) enter into, adopt or amend any UPR Employee Benefit Plan
         or UPR Employment Agreement, except as may be required by Applicable
         Law, other than amendments in the ordinary course consistent with past
         practice that do not increase,


                                      -42-
<PAGE>   47


         reduce or accelerate benefits, make payout options more favorable to
         participants, or otherwise result in any increased cost to UPR;
         provided, however, that UPR may amend its Supplemental Pension Plan for
         Exempt Salaried Employees to add a lump sum distribution option if the
         cost of such distribution option is determined in a manner consistent
         with the actuarial assumptions set forth in Section 5.3(c)(ix) of the
         UPR Disclosure Schedule;

                  (x) take any action that could give rise to a right to
         severance benefits pursuant to any Change in Control Agreement;

                  (xi) change any method or principle of accounting in a manner
         that is inconsistent with past practice except to the extent required
         by United States generally accepted accounting principles as advised by
         UPR's regular independent accountants;

                  (xii) settle any Actions, whether now pending or hereafter
         made or brought involving, individually an amount in excess of $1
         million or in the aggregate, an amount in excess of $20 million;

                  (xiii) modify, amend or terminate, or waive, release or assign
         any material rights or claims with respect to any confidentiality
         agreement to which UPR is a party;

                  (xiv) enter into any confidentiality agreements or
         arrangements other than in the ordinary course of business consistent
         with past practice (other than as permitted, in each case, by Section
         5.3(d));

                  (xv) write up, write down or write off the book value of any
         assets, individually or in the aggregate, in excess of $5 million
         except for depreciation and amortization and provision (e.g.,
         surrendered leases) in accordance with generally accepted accounting
         principles consistently applied utilizing successful efforts accounting
         or as otherwise required by generally accepted accounting principles;

                  (xvi) incur or commit to any capital expenditures not included
         within the dollar limits of the UPR Capital Budget as in effect on the
         date of this Agreement (a copy of which included in Section 5.3(c) to
         the UPR Disclosure Schedule);

                  (xvii) make any payments in respect of policies of directors'
         and officers' liability insurance (premiums or otherwise) other than
         premiums paid in respect of its current policies and renewals thereof
         at the same policy limits;

                  (xviii) take any action to exempt or make not subject to the
         provisions of any state takeover law or state law that purports to
         limit or restrict business combinations or the ability to acquire or
         vote shares, any person or entity (other than Anadarko or its
         subsidiaries) or any action taken thereby, which person, entity or
         action would have otherwise been subject to the restrictive provisions
         thereof and not exempt therefrom;

                  (xix) take any action that would likely result in the
         representations and warranties set forth in Article IV becoming false
         or inaccurate in any material respect;


                                      -43-
<PAGE>   48

                  (xx) enter into or carry out any other transaction other than
         in the ordinary and usual course of business;

                  (xxi) permit or cause any subsidiary to do any of the
         foregoing or agree or commit to do any of the foregoing;

                  (xxii) except as otherwise required by law, make any material
         Tax election, settle or compromise any material Tax claim, file any Tax
         Return (other than in a manner consistent with past practice) or change
         any method of Tax accounting; or

                  (xxiii) agree in writing or otherwise to take any of the
         foregoing actions.

                  (d) No Solicitation. UPR agrees that, during the term of this
Agreement, it shall not, and shall not authorize or permit any of its
subsidiaries or any of its or its subsidiaries' directors, officers, employees,
agents or representatives, directly or indirectly, to solicit, initiate,
encourage or facilitate, or furnish or disclose non-public information in
furtherance of, any inquiries or the making of any proposal with respect to any
recapitalization, merger, consolidation or other business combination involving
UPR, or any acquisition of 15% or more of the capital stock (other than upon
exercise of UPR Options that are outstanding as of the date hereof) or 30% or
more of the assets of UPR and its subsidiaries, taken as a whole, in a single
transaction or a series of related transactions, or any combination of the
foregoing (a "UPR Competing Transaction"), or negotiate, explore or otherwise
engage in discussions with any person (other than Anadarko, Subcorp or their
respective directors, officers, employees, agents and representatives) with
respect to any UPR Competing Transaction or enter into any agreement,
arrangement or understanding requiring it to abandon, terminate or fail to
consummate the Merger or any other transactions contemplated by this Agreement;
provided that, at any time prior to the approval of the Merger by the UPR
Stockholders, UPR may furnish information to, and engage in discussions with,
any party who delivers a written proposal for a UPR Competing Transaction which
was not solicited or encouraged after the date of this Agreement in violation of
this Agreement if and so long as the Board of Directors of UPR determines in
good faith by resolution duly adopted after consultation with its outside
counsel (who may be its regularly engaged outside counsel) that the failure to
take such action would reasonably be expected to constitute a breach of its
fiduciary duties under Applicable Law and determines that such a proposal is,
after consulting with the UPR Financial Advisors, more favorable to UPR
Stockholders from a financial point of view than the transactions contemplated
by this Agreement (including any adjustment to the terms and conditions proposed
by Anadarko in response to such UPR Competing Transaction) (a "UPR Superior
Proposal"); provided, further, that prior to furnishing information to, or
engaging in discussions with, any party pursuant to the foregoing proviso, UPR
shall have received an executed agreement from such party in the same form as
the Confidentiality Agreement (other than Section 8 thereof which shall be
waived for Anadarko under the Confidentiality Agreement upon the execution of
such agreement). UPR will immediately cease all existing activities, discussions
and negotiations with any parties conducted heretofore with respect to any
proposal for a UPR Competing Transaction and request the return of all
confidential information regarding UPR provided to any such parties prior to the
date hereof pursuant to the terms of any confidentiality agreements or
otherwise. In the event that prior to the approval of the Merger by the UPR
Stockholders the Board of Directors of UPR receives a UPR Superior Proposal that
was not solicited or


                                      -44-
<PAGE>   49


encouraged after the date of this Agreement in violation of this Agreement, and
the Board of Directors of UPR determines in good faith by resolution duly
adopted after consultation with its outside counsel (who may be its regularly
engaged outside counsel) that the failure to take such action would reasonably
be expected to constitute a breach of its fiduciary duties under Applicable Law,
the Board of Directors of UPR may (subject to this and the following sentences)
withdraw, modify or change, in a manner adverse to Anadarko, the UPR Board
Recommendation and/or comply with Rule 14e-2 promulgated under the Exchange Act
with respect to a UPR Competing Transaction, provided that it gives Anadarko
three business days' prior written notice of its intention to do so (provided
that the foregoing shall in no way limit or otherwise affect Anadarko's right to
terminate this Agreement pursuant to Section 7.3(b)). Any such withdrawal,
modification or change of the UPR Board Recommendation shall not change the
approval of the Board of Directors of UPR for purposes of causing any state
takeover statute or other state law to be inapplicable to the transactions
contemplated hereby, including the Merger or the UPR Stock Option Agreement or
change the obligation of UPR to present the Merger for approval at a duly called
UPR Stockholders Meeting on the earliest practicable date determined in
consultation with Anadarko. From and after the execution of this Agreement, UPR
shall promptly (but in any event within one calendar day) advise Anadarko in
writing of the receipt, directly or indirectly, of any inquiries, discussions,
negotiations, or proposals relating to a UPR Competing Transaction (including
the specific terms thereof and the identity of the other party or parties
involved) and promptly furnish to Anadarko a copy of any such written proposal
in addition to any information provided to or by any third party relating
thereto. In addition, UPR shall promptly (but in any event within one calendar
day) advise Anadarko, in writing, if the Board of Directors of UPR shall make
any determination as to any UPR Competing Transaction as contemplated by the
proviso to the first sentence of this Section 5.3(d).

                  (e) Affiliates of UPR. UPR shall cause each such person who
may be at the Effective Time or was on the date hereof an "affiliate" of UPR for
purposes of Rule 145 under the Securities Act, to execute and deliver to
Anadarko no less than 30 days prior to the date of the UPR Stockholders Meeting,
the written undertakings in the form attached hereto as Exhibit A (the "UPR
Affiliate Letter"). No later than 45 days prior to such date, UPR, after
consultation with its outside counsel, shall provide Anadarko with a letter
(reasonably satisfactory to outside counsel to Anadarko) specifying all of the
persons or entities who, in UPR's opinion, may be deemed to be "affiliates" of
UPR under the preceding sentence. The foregoing notwithstanding, Anadarko shall
be entitled to place legends as specified in the UPR Affiliate Letter on the
certificates evidencing any of the Anadarko Common Shares to be received by (i)
any such "affiliate" of UPR specified in such letter or (ii) any person Anadarko
reasonably identifies (by written notice to UPR) as being a person who may be
deemed an "affiliate" for purposes of Rule 145 under the Securities Act,
pursuant to the terms of this Agreement, and to issue appropriate stop transfer
instructions to the transfer agent for the Anadarko Common Shares, consistent
with the terms of the UPR Affiliate Letter, regardless of whether such person
has executed the UPR Affiliate Letter and regardless of whether such person's
name appears on the letter to be delivered pursuant to the preceding sentence.

                  (f) Access. UPR shall permit representatives of Anadarko to
have access at all reasonable times to UPR's premises, properties, books,
records, contracts, documents, customers and suppliers. Information obtained by
Anadarko pursuant to this Section 5.3(f) shall be subject to the provisions of
the Confidentiality Agreement, which agreement remains in full force and


                                      -45-
<PAGE>   50

effect. No investigation conducted pursuant to this Section 5.3(f) shall affect
or be deemed to modify any representation or warranty made in this Agreement.

                  (g) Subsequent Financial Statements. UPR shall consult with
Anadarko prior to making publicly available its financial results for any period
after the date of this Agreement and prior to filing any UPR SEC Documents after
the date of this Agreement.

                                   ARTICLE VI.

                                   CONDITIONS

                  6.1 Conditions to the Obligations of Each Party. The
obligations of UPR, Anadarko and Subcorp to consummate the Merger shall be
subject to the satisfaction of the following conditions:

                  (a) (i) This Agreement, the Merger and the transactions
contemplated hereby shall have been approved and adopted by the UPR Stockholders
in the manner required by any Applicable Law, and (ii) the Share Issuance shall
have been approved by the Anadarko Stockholders in the manner required by any
Applicable Law and the applicable rules of the NYSE.

                  (b) Any applicable waiting periods under the HSR Act relating
to the Merger and the transactions contemplated by this Agreement shall have
expired or been terminated and any other approvals of any Governmental Authority
shall have been obtained.

                  (c) No provision of any applicable law or regulation and no
judgment, injunction, order or decree shall prohibit or enjoin the consummation
of the Merger or the transactions contemplated by this Agreement or limiting the
ownership or operation by Anadarko, UPR or any of their respective subsidiaries
of any material portion of the business or assets of Anadarko or UPR.

                  (d) There shall not be pending any Action instituted by any
Governmental Authority challenging or seeking to restrain or prohibit the
consummation of the Merger or any of the other transactions contemplated by this
Agreement.

                  (e) The Commission shall have declared the Registration
Statement effective under the Securities Act, and no stop order or similar
restraining order suspending the effectiveness of the Registration Statement
shall be in effect and no proceedings for such purpose shall be pending before
or threatened by the Commission or any state securities administrator.

                  (f) The Anadarko Common Shares to be issued in the Merger
(including pursuant to Anadarko Exchange Options) shall have been approved for
listing on the NYSE, subject to official notice of issuance.

                  (g) UPR shall have received the opinion of Morgan Lewis &
Bockius LLP, dated on or prior to the effective date of the Registration
Statement, to the effect that (i) the Merger will constitute a reorganization
under section 368(a) of the Code, and (ii) UPR, Anadarko and Subcorp will each
be a party to that reorganization. In rendering such opinion,


                                      -46-
<PAGE>   51

counsel shall be entitled to rely on customary representation letters of UPR,
Anadarko, Subcorp and others, in form and substance reasonably satisfactory to
such counsel.

                  6.2 Conditions to Obligations of UPR. The obligations of UPR
to consummate the Merger and the transactions contemplated hereby shall be
subject to the fulfillment of the following conditions unless waived by UPR:

                  (a) Each of the representations and warranties of each of
Anadarko and Subcorp set forth in Article III (other than the representations
and warranties of Anadarko set forth in Section 3.4) shall be true and correct
in all respects (but without regard to any materiality qualifications or
references to Material Adverse Effect contained in any specific representation
or warranty) on the date of this Agreement and on and as of the Closing Date as
though made on and as of the Closing Date (except for representations and
warranties made as of a specified date, the accuracy of which will be determined
as of the specified date), unless the failure or failures of representations and
warranties to be true and correct in all respects, individually and taken
together with all other such failures, would not reasonably be expected to have
a Material Adverse Effect on Anadarko. The representations and warranties of
Anadarko set forth in Section 3.4 of this Agreement shall be true and correct in
all respects (other than de minimis variations) on the date of this Agreement
and on and as of the Closing Date as though made on and as of the Closing Date
(except for representations and warranties made as of a specified date, the
accuracy of which will be determined as of the specified date).

                  (b) Each of Anadarko and Subcorp shall have performed in all
material respects all obligations and agreements and shall have complied in all
material respects with all covenants to be performed and complied with by it
hereunder at or prior to the Effective Time.

                  (c) Each of Anadarko and Subcorp shall have furnished UPR with
a certificate dated the Closing Date signed on behalf of it by the Chairman or
President to the effect that the conditions set forth in Sections 6.2(a) and (b)
have been satisfied.

                  (d) At any time after the date of this Agreement, there shall
not have been any one or more events or occurrences that individually or in the
aggregate has had or is likely to have a Material Adverse Effect on Anadarko.

                  6.3 Conditions to Obligations of Anadarko and Subcorp. The
obligations of Anadarko and Subcorp to consummate the Merger and the other
transactions contemplated hereby shall be subject to the fulfillment of the
following conditions unless waived by Anadarko:

                  (a) Each of the representations and warranties of UPR set
forth in Article IV (other than the representations and warranties of UPR set
forth in Section 4.4) shall be true and correct in all respects (but without
regard to any materiality qualifications or references to Material Adverse
Effect contained in any specific representation or warranty) on the date of this
Agreement and on and as of the Closing Date as though made on and as of the
Closing Date (except for representations and warranties made as of a specified
date, the accuracy of which will be determined as of the specified date), unless
the failure or failures of representations and warranties to be true and correct
in all respects, individually and taken together with all other such failures,
would not reasonably be expected to have a Material Adverse Effect on UPR. The


                                      -47-
<PAGE>   52

representations and warranties of UPR set forth in Section 4.4 of this Agreement
shall be true and correct in all respects (other than de minimis variations) on
the date of this Agreement and on and as of the Closing Date as though made on
and as of the Closing Date (except for representations and warranties made as of
a specified date, the accuracy of which will be determined as of the specified
date).

                  (b) UPR shall have performed in all material respects all
obligations and agreements and shall have complied in all material respects with
all covenants to be performed and complied with by it hereunder at or prior to
the Effective Time.

                  (c) UPR shall have furnished Anadarko with a certificate dated
the Closing Date signed on its behalf by its Chairman or President to the effect
that the conditions set forth in Sections 6.3(a) and (b) have been satisfied.

                  (d) The agreement referred to in Section 6.3 to the Anadarko
Disclosure Schedule shall be in full force and effect and shall not have been
terminated.

                  (e) At any time after the date of this Agreement, there shall
not have been any one or more events or occurrences that individually or in the
aggregate has had or is likely to have a Material Adverse Effect on UPR.


                                  ARTICLE VII.

                            TERMINATION AND AMENDMENT

                  7.1 Termination by Mutual Consent. This Agreement maybe
terminated at any time prior to the Effective Time by the mutual written consent
of Anadarko and UPR.

                  7.2 Termination by UPR or Anadarko. This Agreement may be
terminated by action of the Board of Directors of UPR or of Anadarko if:

                  (a) the Merger shall not have been consummated by December 31,
2000; provided, however, that in the event that Section 6.1(b), Section 6.1(c)
or Section 6.1(d), or any combination thereof, are the only conditions that are
not satisfied or capable of being immediately satisfied as a result of any
action by any Governmental Authority pursuant to any Antitrust Laws, such
December 31, 2000 date shall be extended for a period not to exceed the lesser
of 90 days or the fifth business day after the entrance by the court in which
such litigation is pending of its decision (whether or not subject to appeal or
rehearing) in such litigation; and provided, further, that the right to
terminate this Agreement pursuant to this clause (a) shall not be available to
any party whose failure or whose affiliate's failure to perform or observe in
any material respect any of its obligations under this Agreement in any manner
shall have been the cause of, or resulted in, the failure of the Merger to occur
on or before such date; or

                  (b) the Anadarko Stockholders Meeting (including adjournments
and postponements) for the purpose of approving the Share Issuance shall have
been held and such stockholder approval shall not have been obtained; or



                                      -48-
<PAGE>   53

                  (c) the UPR Stockholders Meeting (including adjournments and
postponements) for the purpose of approving this Agreement and the Merger shall
have been held and such stockholder approval shall not have been obtained; or

                  (d) a United States federal or state court of competent
jurisdiction or United States federal or state governmental, regulatory or
administrative agency or commission shall have issued an order, decree or ruling
or taken any other action permanently restraining, enjoining or otherwise
prohibiting the Merger and such order, decree, ruling or other action shall have
become final and non-appealable; provided, however, that the party seeking to
terminate this Agreement pursuant to this clause (d) shall have complied with
Section 5.1(a) and with respect to other matters not covered by Section 5.1(a)
shall have used its commercially reasonable best efforts to remove such
injunction, order or decree.

                  7.3 Termination by Anadarko. This Agreement may be terminated
prior to the Effective Time, by action of the Board of Directors of Anadarko
after consultation with its legal advisors, if

                  (a) (i) there has been a breach by UPR of any representation,
warranty, covenant or agreement set forth in this Agreement or if any
representation or warranty of UPR shall have become untrue, in either case such
that the conditions set forth in Section 6.3(a) would not be satisfied and (ii)
such breach is not curable, or, if curable, is not cured within 45 days after
written notice of such breach is given to UPR by Anadarko; provided, however,
that the right to terminate this Agreement pursuant to this Section 7.3(a) shall
not be available to Anadarko if it, at such time, is in material breach of any
representation, warranty, covenant or agreement set forth in this Agreement such
that the condition set forth in Section 6.2(a) shall not be satisfied; or

                  (b) the Board of Directors of UPR shall have withdrawn or
modified, in a manner adverse to Anadarko, its approval or recommendation of
this Agreement or the Merger or recommended a UPR Competing Transaction, or
resolved to do so.

                  7.4 Termination by UPR. This Agreement may be terminated at
any time prior to the Effective Time, by action of the Board of Directors of UPR
after consultation with its legal advisors, if:

                  (a) (i) there has been a breach by Anadarko or Subcorp of any
representation, warranty, covenant or agreement set forth in this Agreement or
if any representation or warranty of Anadarko or Subcorp shall have become
untrue, in either case such that the conditions set forth in Section 6.2(a)
would not be satisfied and (ii) such breach is not curable, or, if curable, is
not cured within 45 days after written notice of such breach is given by UPR to
Anadarko; provided, however, that the right to terminate this Agreement pursuant
to this Section 7.4(a) shall not be available to UPR if it, at such time, is in
material breach of any representation, warranty, covenant or agreement set forth
in this Agreement such that the conditions set forth in Section 6.3(a) shall not
be satisfied; or

                  (b) the Board of Directors of Anadarko shall have withdrawn or
modified, in a manner adverse to UPR, its approval or recommendation of Share
Issuance or recommended a proposal relating to an Anadarko Competing
Transaction, or resolved to do so.


                                      -49-
<PAGE>   54

                  7.5 Effect of Termination.

                  (a) If this Agreement is terminated

               (i) after the public announcement of a proposal relating to a UPR
         Competing Transaction, by Anadarko or UPR pursuant to Section 7.2(c);
         or

               (ii) after the public announcement or receipt by UPR's Board of
         Directors of a proposal relating to a UPR Competing Transaction, by
         Anadarko pursuant to Section 7.3(b);

then UPR shall pay Anadarko a fee of $25 million (subject to reduction pursuant
to Section 9 of the UPR Stock Option Agreement) at the time of such termination
in cash by wire transfer to an account designated by Anadarko. In addition, if
within one year after such termination, UPR enters into a definitive agreement
with respect to a UPR Acquisition (as hereinafter defined) or a UPR Acquisition
is consummated, then upon the consummation of such UPR Acquisition, UPR shall
pay Anadarko an additional fee of $100 million (subject to reduction pursuant to
Section 9 of the UPR Stock Option Agreement) at the time of such consummation in
cash by wire transfer to an account designated by Anadarko. For purposes of this
Agreement, "UPR Acquisition" means (i) consummation of the UPR Competing
Transaction giving rise to the termination described in Section 7.5(a)(i) or
7.5(a)(ii), (ii) a consolidation, exchange of shares or merger of UPR with any
person, other than Anadarko or one of its subsidiaries, and, in the case of a
merger, in which UPR shall not be the continuing or surviving corporation, (iii)
a merger of UPR with a person, other than Anadarko or one of its subsidiaries,
in which UPR shall be the continuing or surviving corporation but the then
outstanding shares of UPR Common Stock shall be changed into or exchanged for
stock or other securities of UPR or any other person or cash or any other
property or the shares of UPR Common Stock outstanding immediately before such
merger shall after such merger represent less than 50% of the voting stock of
UPR outstanding immediately after the merger, (iv) the acquisition of beneficial
ownership of 50% or more of the voting stock of UPR by any person (as such term
is used under Section 13(d) of the Exchange Act), or (v) a sale, lease or other
transfer of 50% or more of the assets of UPR to any person, other than Anadarko
or one of its subsidiaries.

                  (b) If this Agreement is terminated

               (i) after the public announcement of a proposal relating to an
         Anadarko Competing Transaction, by Anadarko or UPR pursuant to Section
         7.2(b); or

               (ii) after the public announcement or receipt by Anadarko's Board
         of Directors of a proposal relating to an Anadarko Competing
         Transaction, by UPR pursuant to Section 7.4(b);

then Anadarko shall pay UPR a fee of $25 million (subject to reduction pursuant
to Section 9 of the Anadarko Stock Option Agreement) at the time of such
termination in cash by wire transfer to an account designated by UPR. In
addition, if within one year after such termination, Anadarko enters into a
definitive agreement with respect to an Anadarko Acquisition or an Anadarko
Acquisition is consummated, then upon the consummation of such Anadarko
Acquisition, Anadarko shall pay UPR an additional fee of $100 million (subject
to reduction


                                      -50-
<PAGE>   55

pursuant to Section 9 of the Anadarko Stock Option Agreement) at the time of
such consummation in cash by wire transfer to an account designated by UPR. For
purposes of this Agreement, "Anadarko Acquisition" means (i) consummation of the
Anadarko Competing Transaction giving rise to the termination described in
Section 7.5(b)(i) or 7.5(b)(ii), (ii) a consolidation, exchange of shares or
merger of Anadarko with any person, other than UPR or one of its subsidiaries,
and, in the case of a merger, in which Anadarko shall not be the continuing or
surviving corporation, (iii) a merger of Anadarko with a person, other than UPR
or one of its Subsidiaries, in which Anadarko shall be the continuing or
surviving corporation but the then outstanding Anadarko Common Shares shall be
changed into or exchanged for stock or other securities of Anadarko or any other
person or cash or any other property or the Anadarko Common Shares outstanding
immediately before such merger shall after such merger represent less than 50%
of the voting stock of Anadarko outstanding immediately after the merger, (iv)
the acquisition of beneficial ownership of 50% or more of the voting stock of
Anadarko by any person (as such term is used under Section 13(d) of the Exchange
Act), or (v) a sale, lease or other transfer of 50% or more of the assets of
Anadarko to any person, other than UPR or one of its subsidiaries.

                  (c) In the event of the termination of this Agreement pursuant
to Section 7.1, Section 7.2, Section 7.3 or Section 7.4, this Agreement, except
for the provisions of the second sentence of each of Section 5.2(g) and Section
5.3(f) and the provisions of Sections 7.5 and 8.11, shall become void and have
no effect, without any liability on the part of any party or its directors,
officers or stockholders. Notwithstanding the foregoing, nothing in this Section
7.5 shall relieve any party to this Agreement of liability for a material breach
of any provision of this Agreement and provided, further, however, that if it
shall be judicially determined that termination of this Agreement was caused by
an intentional breach of this Agreement, then, in addition to other remedies at
law or equity for breach of this Agreement, the party so found to have
intentionally breached this Agreement shall indemnify and hold harmless the
other parties for their respective out-of-pocket costs, fees and expenses of
their counsel, accountants, financial advisors and other experts and advisors as
well as fees and expenses incident to negotiation, preparation and execution of
this Agreement and related documentation and shareholders' meetings and
consents.

                  7.6 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 adoption of this Agreement by UPR Stockholders, but
after any such approval, no amendment shall be made which by law requires
further approval or authorization by the UPR Stockholders without such further
approval or authorization. Notwithstanding the foregoing, this Agreement may not
be amended except by an instrument in writing signed on behalf of each of the
parties hereto.

                  7.7 Extension; Waiver. At any time prior to the Effective
Time, Anadarko (with respect to UPR) and UPR (with respect to Anadarko and
Subcorp) by action taken or authorized by their respective Boards of Directors,
may, to the extent legally allowed, (a) extend the time for the performance of
any of the obligations or other acts of such party, (b) waive any inaccuracies
in the representations and warranties contained herein or in any document
delivered pursuant hereto and (c) waive compliance with any of the agreements or
conditions contained


                                      -51-
<PAGE>   56

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 VIII.

                                  MISCELLANEOUS

                  8.1 Survival of Representations and Warranties. The
representations and warranties made herein by the parties hereto shall not
survive the Effective Time. This Section 8.1 shall not limit any covenant or
agreement of the parties hereto, which by its terms contemplates performance
after the Effective Time or after the termination of this Agreement.

                  8.2 Notices. All notices and other communications hereunder
shall be in writing and shall be deemed given if delivered personally,
telecopied (which is confirmed) or dispatched by a nationally recognized
overnight courier service 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 Anadarko or Subcorp:

                             Anadarko Petroleum Corporation
                             17001 Northchase Drive
                             Houston, Texas  77060
                             Attention:  J. Stephen Martin
                             Telecopy  No.:  (281) 874-3296

                             with a copy to

                             Daniel A. Neff, Esq.
                             David A. Katz, Esq.
                             Wachtell, Lipton, Rosen & Katz
                             51 West 52nd Street
                             New York, New York  10019
                             Telecopy No.:  (212) 403-2000

                  (b) if to UPR:

                             UPR
                             UPR Plaza, 777 Main Street
                             Fort Worth, Texas  76102
                             Attention: Kerry R. Brittain
                             Telecopy No.:  (817) 321-7026



                                      -52-
<PAGE>   57


                             with a copy to

                             Howard L. Shecter, Esq.
                             Morgan Lewis & Bockius LLP
                             101 Park Avenue
                             New York, New York 10178
                             Telecopy No:  (212) 309-6273

                  8.3 Interpretation. When a reference is made in this Agreement
to an Article or Section, such reference shall be to an Article or Section of
this Agreement unless otherwise indicated. The headings and the table of
contents contained in this Agreement are for reference purposes only and shall
not affect in any way the meaning or interpretation of this Agreement. When a
reference is made in this Agreement to UPR, such reference shall be deemed to
include any and all subsidiaries of UPR, individually and in the aggregate,
except for Sections 4.1, 4.2, 4.3, 4.4, 4.5, 4.8, 4.10, 4.19, 4.20, 4.21 and
4.22. When a reference is made in this Agreement to Anadarko, such reference
shall be deemed to include any and all subsidiaries of Anadarko, individually
and in the aggregate, except for Sections 3.1, 3.2, 3.3, 3.4, 3.5, 3.8, 3.10,
3.19, 3.20, 3.21 and 3.22. For purposes of any provision of this Agreement,
references to "knowledge" with respect to Anadarko shall be deemed to be to the
actual knowledge of persons listed in Section 8.3 to the Anadarko Disclosure
Schedule, and references to "knowledge" with respect to UPR shall be deemed to
be to the actual knowledge of persons listed in Section 8.3 to the UPR
Disclosure Schedule. For the purposes of any provision of this Agreement, a
"Material Adverse Effect" with respect to any party shall be deemed to occur if
the aggregate consequences of all breaches and inaccuracies of covenants and
representations of such party under this Agreement, when read without any
exception or qualification for a material adverse effect, are reasonably likely
to have a material adverse effect on the business, assets, liabilities, results
of operations, financial condition or prospects of such party and its
subsidiaries taken as a whole, other than any change, circumstance or effect
relating to (x) the economy or financial markets in general, or (y) the price of
oil or gas. For purposes of this Agreement, a "subsidiary" when used with
respect to any party means any corporation or other organization, incorporated
or unincorporated, (i) of which such party or another subsidiary of such party
is a general partner or (ii) 50% or more of the securities or other interests of
which having by their terms ordinary voting power to elect at least 50% 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 one or more of its subsidiaries (or if there are no such voting
securities or interests, 50% or more of the equity interests of which is
directly or indirectly owned or controlled by such party or one or more of its
subsidiaries).

                  8.4 Counterparts. This Agreement may be executed in
counterparts, which together shall constitute one and the same Agreement. The
parties may execute more than one copy of the Agreement, each of which shall
constitute an original.

                  8.5 Entire Agreement. This Agreement (including the documents
and the instruments referred to herein), the Anadarko Stock Option Agreement,
the UPR Stock Option Agreement and the Confidentiality Agreement constitute the
entire agreement among the parties and supersede all prior agreements and
understandings, agreements or representations by or among the parties, written
and oral, with respect to the subject matter hereof and thereof.



                                      -53-
<PAGE>   58
                  8.6 Third-Party Beneficiaries. Except for the agreement set
forth in Section 5.2(e), nothing in this Agreement, express or implied, is
intended or shall be construed to create any third-party beneficiaries.

                  8.7 Governing Law. Except to the extent that the laws of the
jurisdiction of organization of any party hereto, or any other jurisdiction, are
mandatorily applicable to the Merger or to matters arising under or in
connection with this Agreement, this Agreement shall be governed by the laws of
the State of Delaware. All actions and proceedings arising out of or relating to
this Agreement shall be heard and determined in any state or federal court
sitting in the City of Wilmington, Delaware.

                  8.8 Consent to Jurisdiction; Venue.

                  (a) Each of the parties hereto irrevocably submits to the
exclusive jurisdiction of the state courts of Delaware and to the jurisdiction
of the United States District Court for the District of Delaware, for the
purpose of any action or proceeding arising out of or relating to this Agreement
and each of the parties hereto irrevocably agrees that all claims in respect to
such action or proceeding may be heard and determined exclusively in any
Delaware state or federal court sitting in the City of Wilmington, Delaware.
Each of the parties hereto agrees that a final judgment in any action or
proceeding shall be conclusive and may be enforced in other jurisdictions by
suit on the judgment or in any other manner provided by law.

                  (b) Each of the parties hereto irrevocably consents to the
service of any summons and complaint and any other process in any other action
or proceeding relating to the Merger, on behalf of itself or its property, by
the personal delivery of copies of such process to such party. Nothing in this
Section 8.8 shall affect the right of any party hereto to serve legal process in
any other manner permitted by law.

                  8.9 Specific Performance. The transactions contemplated by
this Agreement are unique. Accordingly, each of the parties acknowledges and
agrees that, in addition to all other remedies to which it may be entitled, each
of the parties hereto is entitled to a decree of specific performance, provided
such party is not in material default hereunder.

                  8.10 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. Subject to the preceding sentence, this Agreement
shall be binding upon, inure to the benefit of and be enforceable by the parties
and their respective successors and assigns.

                  8.11 Expenses. Subject to the provisions of Section 7.5, all
costs and expenses incurred in connection with this Agreement and the
transactions contemplated hereby and thereby shall be paid by the party
incurring such expenses, except that those expenses incurred in connection with
filing, printing and mailing the Registration Statement and the Joint Proxy
Statement (including filing fees related thereto) will be shared equally by
Anadarko and UPR.



                                      -54-
<PAGE>   59


                  IN WITNESS WHEREOF, Anadarko, Subcorp and UPR have signed this
Agreement as of the date first written above.


                              ANADARKO PETROLEUM CORPORATION


                              By: /s/ Robert J. Allison
                                 -----------------------------------------------
                                 Name:  Robert J. Allison
                                 Title: Chairman and Chief Executive Officer



                              DAKOTA MERGER CORP.


                              By: /s/ Robert J. Allison
                                 -----------------------------------------------
                                 Name:  Robert J. Allison
                                 Title: Chairman




                              UNION PACIFIC RESOURCES GROUP INC.


                              By: /s/ George Lindahl, III
                                 -----------------------------------------------
                                 Name:  George Lindahl, III
                                 Title: Chairman, President and Chief Executive
                                        Officer



<PAGE>   60

                                                                       EXHIBIT A

                        FORM OF COMPANY AFFILIATE LETTER

                                                            _____________, 2000

Anadarko Petroleum Corporation
17001 Northchase Drive
Houston, Texas  77060


Ladies and Gentlemen:

         The undersigned, a holder of shares of common stock, no par value
(together with each associated purchase right, the "UPR Common Stock"), of UPR
Inc., a Utah corporation ("UPR"), has been advised that as of the date hereof,
the undersigned may be deemed to be an "affiliate" of UPR, as the term
"affiliate" is defined for purposes of paragraphs (c) and (d) of Rule 145 of the
Rules and Regulations of the Securities and Exchange Commission.

         The undersigned has been further advised that, pursuant to the terms of
the Agreement and Plan of Merger, dated as of April 2, 2000, as amended (the
"Merger Agreement"), by and between Anadarko Petroleum Corporation, a Delaware
corporation ("Anadarko"), Dakota Merger Corp., a Utah corporation and a wholly
owned subsidiary of Anadarko ("Subcorp"), and UPR, Subcorp may be merged with
and into UPR, and as a result of such merger (the "Merger"), the undersigned
will receive Anadarko Common Shares (as defined in the Merger Agreement) in
exchange for shares of UPR Common Stock owned by the undersigned.

         1. The undersigned represents, warrants and covenants that the
undersigned:

                  A. Has read carefully this letter and discussed applicable
         limitations upon the ability of the undersigned to sell, transfer or
         otherwise dispose of Anadarko Common Shares to the extent the
         undersigned believes necessary with counsel of the undersigned or
         counsel for UPR.

                  B. Has been advised that the issuance of Anadarko Common
         Shares to the undersigned pursuant to the Merger will be registered
         with the Commission under the Securities Act of 1933, as amended (the
         "Securities Act"), on a Registration Statement on Form S-4. However,
         the undersigned has also been advised that, because the undersigned may
         be deemed to have been an affiliate of UPR at the time the Merger
         Agreement and Merger were submitted for a vote of the stockholders of
         UPR and because the distribution by the undersigned of Anadarko Common
         Shares has not been registered under the Securities Act, the
         undersigned may not sell, transfer or otherwise dispose of Anadarko
         Common Shares issued to the undersigned in the Merger unless (i) such
         sale, transfer or other disposition has been registered under the
         Securities Act, (ii) such sale, transfer or other disposition is made
         in conformity with the volume and other limitations of Rule 145
         promulgated by the Commission under the Securities Act, or (iii) the
         undersigned delivers an opinion of counsel reasonably acceptable to
         Anadarko, or a "no-action" or interpretive letter of the Commission is
         furnished to Anadarko, stating that such sale, transfer or other
         disposition is otherwise exempt from registration under the Securities
         Act.


                                      A-1

<PAGE>   61

                  C. Understands that Anadarko is under no obligation to
         register the sale, transfer or other disposition of Anadarko Common
         Shares by the undersigned or on behalf of the undersigned under the
         Securities Act or to take any other action necessary in order to make
         compliance with an exemption from such registration available.

                  D. Also understands that Anadarko may give stop-transfer
         instructions to its transfer agent with respect to Anadarko Common
         Shares to enforce the restrictions on the undersigned set forth herein
         and that it reserves the right to place on the certificates for
         Anadarko Common Shares issued to the undersigned, or any substitutions
         therefor, a legend stating in substance:

                           The securities represented by this certificate have
                  been issued in a transaction to which Rule 145 promulgated
                  under the Securities Act of 1933 applies and may be sold or
                  otherwise transferred only in compliance with the requirements
                  of Rule 145 or pursuant to a registration statement under said
                  Act or an exemption from such registration.

                  E. Also understands that unless the transfer by the
         undersigned of Anadarko Common Shares of the undersigned has been
         registered under the Act or is a sale made in conformity with the
         provisions of Rule 145, Anadarko reserves the right to put the
         following legend on the certificates issued to transferees of the
         undersigned:

                           The securities represented by this certificate have
                  not been registered under the Securities Act of 1933 and were
                  acquired from a person who received such shares in a
                  transaction to which Rule 145 promulgated under the Securities
                  Act of 1933 applies. The securities have been acquired by the
                  holder not with a view to, or for resale in connection with,
                  any distribution thereof within the meaning of the Securities
                  Act of 1933 and may not be sold, pledged or otherwise
                  transferred except in accordance with an exemption from the
                  registration requirements of the Securities Act of 1933.

                  F. Neither the execution of this letter nor any provisions set
         forth herein shall be construed as an admission on the part of the
         undersigned that the undersigned is an affiliate of UPR as described in
         the first paragraph of this letter, or as a waiver of any rights the
         undersigned may have to object to any claim that the undersigned is
         such an affiliate on or after the date of this letter.

         2. By Anadarko's acceptance of this letter, Anadarko hereby agrees with
the undersigned to the extent applicable as follows:

                  A. For so long as and to the extent necessary to permit the
         undersigned to sell Anadarko Common Shares pursuant to Rule 145 and, to
         the extent applicable, Rule 144 under the Act, Anadarko shall (a) use
         its reasonable efforts to (i) file, on a timely basis, all reports and
         data required to be filed with the Commission by it pursuant to Section
         13 of the Securities Exchange Act of 1934, as amended (the "Exchange
         Act"), and (ii) furnish to the undersigned upon request a written
         statement as to whether Anadarko has complied with such reporting
         requirements during the 12 months preceding any proposed


                                      A-2

<PAGE>   62

         sale of Anadarko Common Shares by the undersigned under Rule 145, and
         (b) otherwise use its reasonable efforts to permit such sales pursuant
         to Rule 145 and Rule 144. Anadarko and UPR have filed all reports
         required to be filed with the Commission under Section 13 of the
         Exchange Act during the preceding 12 months.

                  B. It is understood and agreed that certificates with the
         legend set forth in paragraphs 1.D and 1.E above will be substituted by
         delivery of certificates without such legend if (i) one year shall have
         elapsed from the date the undersigned received Anadarko Common Shares
         in the Merger and the provisions of Rule 145(d)(2) are then available
         to the undersigned, (ii) two years shall have elapsed from the date the
         undersigned received Anadarko Common Shares in the Merger and the
         provisions of Rule 145(d)(3) are then applicable to the undersigned, or
         (iii) Anadarko has received either an opinion of counsel, which opinion
         and counsel shall be reasonably satisfactory to it, or a "no-action" or
         interpretive letter obtained by the undersigned from the staff of the
         Commission, to the effect that the restrictions imposed by Rule 144 and
         Rule 145 under the Securities Act no longer apply to the undersigned.


                                      A-3

<PAGE>   63





                                          Very truly yours,

                                          --------------------------------------
                                          Signature


                                          --------------------------------------
                                          Print Name

ACCEPTED:

Dated:

ANADARKO PETROLEUM CORPORATION

By:
   ------------------------------
     Name:
     Title:

Dated:




                                      A-4



<PAGE>   1
                                                                     EXHIBIT 2.2


                                                                  CONFORMED COPY


                                       UPR
                             STOCK OPTION AGREEMENT


                  This STOCK OPTION AGREEMENT dated as of April 2, 2000 is by
and between Union Pacific Resources Group Inc., a Utah corporation ("UPR"), and
Anadarko Petroleum Corporation, a Delaware corporation (the "Grantee").

                                    RECITALS

                  The Grantee, Utah and Subcorp propose to enter into the Merger
Agreement providing, among other things, for the Merger pursuant to the Merger
Agreement of Subcorp with and into UPR which shall be the surviving corporation.

                  As a condition and inducement to the Grantee's willingness to
enter into the Merger Agreement, the Grantee has requested that UPR agree, and
UPR has agreed, to grant the Grantee the UPR Stock Option.

                  As a condition and inducement to UPR's willingness to enter
into the Merger Agreement, UPR has separately requested that the Grantee agree,
and the Grantee has agreed, to grant UPR the Anadarko Stock Option pursuant to
the Anadarko Stock Option Agreement dated as of April 2, 2000 by and between the
Grantee and UPR.

                  The Board of Directors of UPR has approved the Merger
Agreement, the Merger and this Agreement and has recommended approval of the
Merger Agreement by the holders of UPR Common Stock.

                  The Board of Directors of the Grantee has approved the Merger
Agreement, the Merger and this Agreement and has recommended approval of the
issuance of shares of Anadarko Common Shares pursuant to the Merger Agreement by
the holders of Anadarko Common Shares.

                  NOW, THEREFORE, in consideration of the foregoing and the
respective representations, warranties, covenants and agreements set forth
herein and in the Merger Agreement, UPR and the Grantee agree as follows:

                  1. Capitalized Terms. Those capitalized terms used but not
defined herein that are defined in the Merger Agreement are used herein with the
same meanings as ascribed to them therein. Those capitalized terms used in this
Agreement that are not defined in the Merger Agreement or in this Agreement are
defined in Annex A hereto and are used herein with the meanings ascribed to them
therein.

                  2. The UPR Stock Option.

                  (a) Grant of UPR Stock Option. Subject to the terms and
conditions set forth herein, UPR hereby grants to the Grantee an irrevocable
option to purchase, out of the authorized but unissued UPR Common Stock,
50,138,515 shares of UPR Common Stock (as adjusted as set forth herein) (the
"UPR Stock Option Shares"), at the Exercise Price.


<PAGE>   2


                  (b) Exercise Price. The exercise price (the "Exercise Price")
of the UPR Stock Option shall be the lesser of (i) $17.60 per UPR Stock Option
Share and (ii) the Exchange Ratio multiplied by the closing price of Anadarko
Common Shares on the date of exercise of the UPR Stock Option.

                  (c) Term. The UPR Stock Option shall be exercisable at any
time and from time to time following the occurrence of an Exercise Event and
shall remain in full force and effect until the earliest to occur of (i) the
Effective Time, (ii) the first anniversary of the receipt by Grantee of written
notice from UPR of the occurrence of an Exercise Event and (iii) termination of
the Merger Agreement in accordance with its terms prior to the occurrence of an
Exercise Event unless such termination itself constitutes an Exercise Event (the
"UPR Stock Option Term"). If the UPR Stock Option is not theretofore exercised,
the rights and obligations set forth in this Agreement shall terminate at the
expiration of the UPR Stock Option Term.

                  (d) Exercise of UPR Stock Option.

                  (i) The Grantee may exercise the UPR Stock Option, in whole or
in part, at any time and from time to time during the UPR Stock Option Term.
Notwithstanding the expiration of the UPR Stock Option Term, the Grantee shall
be entitled to purchase those UPR Stock Option Shares with respect to which it
has exercised the UPR Stock Option in accordance with the terms hereof prior to
the expiration of the UPR Stock Option Term.

                  (ii) If the Grantee wishes to exercise the UPR Stock Option,
it shall send a written notice (an "Exercise Notice") (the date of which being
herein referred to as the "Notice Date") to UPR specifying (i) the total number
of UPR Stock Option Shares it intends to purchase pursuant to such exercise and
(ii) a place and a date (the "Closing Date") not earlier than three Business
Days nor later than 15 Business Days from the Notice Date for the closing of the
purchase and sale pursuant to the UPR Stock Option (the "Closing").

                  (iii) If the Closing cannot be effected by reason of the
application of any Applicable Law, the Closing Date shall be extended to the
tenth Business Day following the expiration or termination of the restriction
imposed by such Applicable Law. Without limiting the foregoing, if prior
notification to, or Authorization of, any Governmental Authority is required in
connection with the purchase of such UPR Stock Option Shares by virtue of the
application of such Applicable Law, the Grantee and, if applicable, UPR shall
promptly file the required notice or application for Authorization and the
Grantee, with the cooperation of UPR, shall expeditiously process the same.

                  (iv) Notwithstanding Section 2(d)(iii), if the Closing Date
shall not have occurred within nine months after the related Notice Date as a
result of one or more restrictions imposed by the application of any Applicable
Law, the exercise of the UPR Stock Option effected on the Notice Date shall be
deemed to have expired.

                  (e) Payment and Delivery of Certificates.

                  (i) At each Closing, the Grantee shall pay to UPR in
immediately available funds by wire transfer to a bank account designated by UPR
an amount equal to the Exercise


                                       2
<PAGE>   3


Price multiplied by the number of UPR Stock Option Shares to be purchased on
such Closing Date.

                  (ii) At each Closing, simultaneously with the delivery of
immediately available funds as provided above, UPR shall deliver to the Grantee
a certificate or certificates representing the UPR Stock Option Shares to be
purchased at such Closing, which UPR Stock Option Shares shall be duly
authorized, validly issued, fully paid and nonassessable and free and clear of
all Liens, and the Grantee shall deliver to UPR its written agreement that the
Grantee will not offer to sell or otherwise dispose of such UPR Stock Option
Shares in violation of applicable Law or the provisions of this Agreement.

                  (f) Certificates. Certificates for the UPR Stock Option Shares
delivered at each Closing shall be endorsed with a restrictive legend that shall
read substantially as follows:

                  THE TRANSFER OF THE STOCK REPRESENTED BY THIS CERTIFICATE IS
         SUBJECT TO RESTRICTIONS ARISING UNDER THE SECURITIES ACT OF 1933, AS
         AMENDED, AND PURSUANT TO THE TERMS OF A UPR STOCK OPTION AGREEMENT
         DATED AS OF APRIL 2, 2000. A COPY OF SUCH AGREEMENT WILL BE PROVIDED TO
         THE HOLDER HEREOF WITHOUT CHARGE UPON RECEIPT BY UPR OF A WRITTEN
         REQUEST THEREFOR.

A new certificate or certificates evidencing the same number of shares of UPR
Common Stock will be issued to the Grantee in lieu of the certificate bearing
the above legend, and such new certificate shall not bear such legend, insofar
as it applies to the Securities Act, if the Grantee shall have delivered to UPR
a copy of a letter from the staff of the Commission, or an opinion of counsel in
form and substance reasonably satisfactory to UPR and its counsel, to the effect
that such legend is not required for purposes of the Securities Act.

                  (g) If at the time of issuance of any UPR Common Stock
pursuant to any exercise of the UPR Stock Option, UPR shall have issued any
share purchase rights or similar securities to holders of UPR Common Stock, then
each UPR Stock Option Share purchased pursuant to the UPR Stock Option shall
also include rights with terms substantially the same as and at least as
favorable to the Grantee as those issued to other holders of UPR Common Stock.

                  3. Adjustment Upon Changes in Capitalization, Etc.

                  (a) In the event of any change in UPR Common Stock by reason
of a stock dividend, split-up, combination, recapitalization, exchange of shares
or similar transaction, the type and number of shares or securities subject to
the UPR Stock Option, and the Exercise Price therefor, shall be adjusted
appropriately, and proper provision shall be made in the agreements governing
such transaction, so that the Grantee shall receive upon exercise of the UPR
Stock Option the same class and number of outstanding shares or other securities
or property that Grantee would have received in respect of UPR Common Stock if
the UPR Stock Option had been exercised immediately prior to such event, or the
record date therefor, as applicable.

                  (b) If any additional shares of UPR Common Stock are issued
after the date of this Agreement (other than pursuant to an event described in
Section 3(a) above), the number of


                                       3
<PAGE>   4


shares of UPR Common Stock then remaining subject to the UPR Stock Option shall
be adjusted so that, after such issuance of additional shares, such number of
shares then remaining subject to the UPR Stock Option, together with shares
theretofore issued pursuant to the UPR Stock Option, equals 19.9% of the number
of shares of UPR Common Stock then issued and outstanding.

                  (c) To the extent any of the provisions of this Agreement
apply to the Exercise Price, they shall be deemed to refer to the Exercise Price
as adjusted pursuant to this Section 3.

                  4. Retention of Beneficial Ownership. To the extent that the
Grantee shall exercise the UPR Stock Option, the Grantee shall, unless the
Grantee shall exercise the Put Right or UPR shall exercise the Call Right,
retain sole ownership of the shares of UPR Common Stock so acquired through the
end of the Call Period.

                  5. Repurchase at the Option of Grantee.

                  (a) At the request of the Grantee made at any time and from
time to time after the occurrence of an Exercise Event and prior to the earlier
of (i) 120 days after the expiration of the UPR Stock Option Term and (ii) 120
days after the conditions to the payment by UPR of the additional $100 million
fee under Section 7.5(a) of the Merger Agreement shall have occurred (the "Put
Period"), UPR (or any successor thereto) shall, at the election of the Grantee
(the "Put Right"), repurchase from the Grantee (i) that portion of the UPR Stock
Option relating to all or any part of the Unexercised UPR Stock Option Shares
(or as to which the UPR Stock Option has been exercised but the Closing has not
occurred) and (ii) all or any portion of the UPR Stock Option Shares purchased
by the Grantee pursuant hereto and with respect to which the Grantee then has
ownership. The date on which the Grantee exercises its rights under this Section
5 is referred to as the "Put Date." Such repurchase shall be at an aggregate
price (the "Put Consideration") equal to the sum of:

                           (i) the aggregate Exercise Price paid by the Grantee
                  for any UPR Stock Option Shares which the Grantee owns and as
                  to which the Grantee is exercising the Put Right;

                           (ii) the excess, if any, of the Applicable Price over
                  the Exercise Price paid by the Grantee for each UPR Stock
                  Option Share as to which the Grantee is exercising the Put
                  Right multiplied by the number of such shares; and

                           (iii) the excess, if any, of (x) the Applicable Price
                  per share of UPR Common Stock over (y) the Exercise Price
                  multiplied by the number of Unexercised UPR Stock Option
                  Shares as to which the Grantee is exercising the Put Right.

                  (b) If the Grantee exercises its rights under this Section 5,
UPR shall, within five Business Days after the Put Date, pay the Put
Consideration to the Grantee in immediately available funds, and the Grantee
shall surrender to UPR the UPR Stock Option or portion of the UPR Stock Option
and the certificates evidencing the UPR Stock Option Shares purchased
thereunder. The Grantee shall warrant to UPR that, immediately prior to the
repurchase thereof


                                       4
<PAGE>   5



pursuant to this Section 5, the Grantee had sole record and Beneficial Ownership
of the UPR Stock Option or such shares, or both, as the case may be, and that
the UPR Stock Option or such shares, or both, as the case may be, were then held
free and clear of all Liens.

                  (c) If the UPR Stock Option has been exercised, in whole or in
part, as to any UPR Stock Option Shares subject to the Put Right but the Closing
thereunder has not occurred, the payment of the Put Consideration shall, to that
extent, render such exercise null and void.

                  (d) Notwithstanding any provision to the contrary in this
Agreement, the Grantee may not exercise its rights pursuant to this Section 5 in
a manner that would result in Total Profit of more than the Profit Cap;
provided, however, that nothing in this sentence shall limit the Grantee's
ability to exercise the UPR Stock Option in accordance with its terms.

                  6. Repurchase at the Option of UPR.

                  (a) To the extent the Grantee shall not have previously
exercised its rights under Section 5, at the request of UPR made at any time
during the 120-day period commencing at the expiration of the Put Period (the
"Call Period"), UPR may repurchase from the Grantee, and the Grantee shall sell,
or cause to be sold, to UPR, all (but not less than all) of the shares of UPR
Common Stock acquired by the Grantee pursuant hereto and with respect to which
the Grantee has ownership at the time of such repurchase at a price per share
equal to the greater of (A) the Current Market Price and (B) the Exercise Price
per share in respect of the shares so acquired (such price per share multiplied
by the number of shares of UPR Common Stock to be repurchased pursuant to this
Section 6 being herein called the "Call Consideration"). The date on which UPR
exercises its rights under this Section 6 is referred to as the "Call Date."

                  (b) If UPR exercises its rights under this Section 6, UPR
shall, within five Business Days pay the Call Consideration in immediately
available funds, and the Grantee shall surrender to UPR certificates evidencing
the shares of UPR Common Stock purchased hereunder, and the Grantee shall
warrant to UPR that, immediately prior to the repurchase thereof pursuant to
this Section 6, the Grantee had sole record and Beneficial Ownership of such
shares and that such shares were then held free and clear of all Liens.

                  7. Registration Rights.

                  (a) UPR shall, if requested by the Grantee at any time and
from time to time during the Registration Period, as expeditiously as
practicable, prepare, file and cause to be made effective up to two registration
statements under the Securities Act if such registration is required in order to
permit the offering, sale and delivery of any or all shares of UPR Common Stock
or other securities that have been acquired by or are issuable to the Grantee
upon exercise of the UPR Stock Option in accordance with the intended method of
sale or other disposition stated by the Grantee, including, at the sole
discretion of UPR, a "shelf" registration statement under Rule 415 under the
Securities Act or any successor provision, and UPR shall use all reasonable
efforts to qualify such shares or other securities under any applicable state
securities laws. UPR shall use all reasonable efforts to cause each such
registration statement to become effective, to obtain all consents or waivers of
other parties that are required therefor and to keep such registration statement
effective for such period not in excess of 180 days from the day such
registration


                                       5
<PAGE>   6


statement first becomes effective as may be reasonably necessary to effect such
sale or other disposition. The obligations of UPR hereunder to file a
registration statement and to maintain its effectiveness may be suspended for
one or more periods of time not exceeding 60 days in the aggregate if the Board
of Directors of UPR shall have determined in good faith that the filing of such
registration or the maintenance of its effectiveness would require disclosure of
nonpublic information that would materially and adversely affect UPR. For
purposes of determining whether two requests have been made under this Section
7, only requests relating to a registration statement that has become effective
under the Securities Act and pursuant to which the Grantee has disposed of all
shares covered thereby in the manner contemplated therein shall be counted.
Notwithstanding any other provision of this Section 7, any request for
registration shall permit UPR, upon notice given within 20 days of the request
for registration, to repurchase from the Grantee any shares as to which the
Grantee requests registration at a price per share equal to the Current Market
Price at the date UPR notifies the Grantee of its decision to so repurchase.

                  (b) The Registration Expenses shall be for the account of UPR;
provided, however, that UPR shall not be required to pay any Registration
Expenses with respect to such registration if the registration request is
subsequently withdrawn at the request of the Grantee unless the Grantee agrees
to forfeit its right to request one registration.

                  (c) The Grantee shall provide all information reasonably
requested by UPR for inclusion in any registration statement to be filed
hereunder. If during the Registration Period UPR shall propose to register under
the Securities Act the offering, sale and delivery of UPR Common Stock for cash
for its own account or for any other stockholder of UPR pursuant to a firm
underwriting, it shall, in addition to UPR's other obligations under this
Section 7, allow the Grantee the right to participate in such registration
provided that the Grantee participates in the underwriting; provided, however,
that, if the managing underwriter of such offering advises UPR in writing that
in its opinion the number of shares of UPR Common Stock requested to be included
in such registration exceeds the number that can be sold in such offering, UPR
shall, after fully including therein all securities to be sold by UPR, include
the shares requested to be included therein by Grantee pro rata (based on the
number of shares intended to be included therein) with the shares intended to be
included therein by Persons other than UPR.

                  (d) In connection with any offering, sale and delivery of UPR
Common Stock pursuant to a registration statement effected pursuant to this
Section 7, UPR and the Grantee shall provide each other and each underwriter of
the offering with customary representations, warranties and covenants, including
covenants of indemnification and contribution.

                  8. First Refusal. Subject to the provisions of Sections 5 and
6 herein, at any time after the first occurrence of an Exercise Event and prior
to the second anniversary of the first purchase of shares of UPR Common Stock
pursuant to the UPR Stock Option, if the Grantee shall desire to sell, assign,
transfer or otherwise dispose of all or any of the UPR Stock Option Shares or
other securities acquired by it pursuant to the UPR Stock Option, it shall give
UPR written notice of the proposed transaction (an "Offeror's Notice"),
identifying the proposed transferee, accompanied by a copy of a binding offer to
purchase such shares or other securities signed by such transferee and setting
forth the terms of the proposed transaction. An Offeror's Notice shall be deemed
an offer by the Grantee to UPR, which may be accepted, in whole but not


                                       6
<PAGE>   7


in part, within 20 Business Days of the receipt of such Offeror's Notice, on the
same terms and conditions and at the same price at which the Grantee is
proposing to transfer such shares or other securities to such transferee. The
purchase of any such shares or other securities by UPR shall be settled within
20 Business Days of the date of the acceptance of the offer and the purchase
price shall be paid to the Grantee in immediately available funds. If UPR shall
fail or refuse to purchase all the shares or other securities covered by an
Offeror's Notice, the Grantee may, within 60 days from the date of the Offeror's
Notice, sell all, but not less than all, of such shares or other securities to
the proposed transferee at no less than the price specified and on terms no more
favorable than those set forth in the Offeror's Notice; provided, however, that
the provisions of this sentence shall not limit the rights the Grantee may
otherwise have if UPR has accepted the offer contained in the Offeror's Notice
and wrongfully refuses to purchase the shares or other securities subject
thereto. The requirements of this Section 8 shall not apply to (a) any
disposition as a result of which the proposed transferee would own beneficially
not more than 2% of the outstanding voting power of UPR, (b) any disposition of
UPR Common Stock or other securities by a Person to whom the Grantee has
assigned its rights under the UPR Stock Option with the consent of UPR, (c) any
sale by means of a public offering registered under the Securities Act or (d)
any transfer to a wholly owned subsidiary of the Grantee which agrees in writing
to be bound by the terms hereof.

                  9. Profit Limitation.

                  (a) Notwithstanding any other provision of this Agreement, in
no event shall the Grantee's Total Profit exceed the Profit Cap and, if it
otherwise would exceed such amount, the Grantee, at its sole election, shall
either (i) deliver to UPR for cancellation UPR Stock Option Shares previously
purchased by Grantee, (ii) pay cash or other consideration to UPR, (iii) reduce
the amount of the fee payable to Grantee under Section 7.5(a) of the Merger
Agreement or (iv) undertake any combination thereof, so that the Grantee's Total
Profit shall not exceed the Profit Cap after taking into account the foregoing
actions.

                  (b) Notwithstanding any other provision of this Agreement,
this UPR Stock Option may not be exercised for a number of UPR Stock Option
Shares that would, as of the Notice Date, result in a Notional Total Profit of
more than the Profit Cap, and, if exercise of the UPR Stock Option otherwise
would exceed the Profit Cap, the Grantee, at its sole UPR Stock Option, may
increase the Exercise Price for that number of UPR Stock Option Shares set forth
in the Exercise Notice so that the Notional Total Profit shall not exceed the
Profit Cap; provided, however, that nothing in this sentence shall restrict any
exercise of the UPR Stock Option otherwise permitted by this Section 9(b) on any
subsequent date at the Exercise Price set forth in Section 2(b) if such exercise
would not then be restricted under this Section 9(b).

                  10. Listing. If UPR Common Stock or any other securities then
subject to the UPR Stock Option are then listed on the NYSE, UPR, upon the
occurrence of an Exercise Event, will promptly file an application to list on
the NYSE the shares of UPR Common Stock or other securities then subject to the
UPR Stock Option and will use all reasonable efforts to cause such listing
application to be approved as promptly as practicable.

                  11. Replacement of Agreement. Upon receipt by UPR of evidence
reasonably satisfactory to it of the loss, theft, destruction or mutilation of
this Agreement, and (in the case of


                                       7
<PAGE>   8


loss, theft or destruction) of reasonably satisfactory indemnification, and upon
surrender and cancellation of this Agreement, if mutilated, UPR will execute and
deliver a new Agreement of like tenor and date. Any such new Agreement shall
constitute an additional contractual obligation of UPR, whether or not the
Agreement so lost, stolen, destroyed or mutilated shall at any time be
enforceable by anyone.

                  12. Miscellaneous.

                  (a) Expenses. Except as otherwise provided in the Merger
Agreement or as otherwise expressly provided herein, each of the parties hereto
shall bear and pay all costs and expenses incurred by it or on its behalf in
connection with the transactions contemplated hereunder, including fees and
expenses of its own financial consultants, investment bankers, accountants and
counsel.

                  (b) Waiver and Amendment. Any provision of this Agreement may
be waived at any time by the party that is entitled to the benefits of such
provision. This Agreement may not be modified, amended, altered or supplemented
except upon the execution and delivery of a written agreement executed by the
parties hereto.

                  (c) Entire Agreement; No Third Party Beneficiary;
Severability. Except as otherwise set forth in the Merger Agreement, this
Agreement (including the Merger Agreement and the other documents and
instruments referred to herein and therein) (i) constitutes the entire agreement
and supersedes all prior agreements and understandings, both written and oral,
between the parties with respect to the subject matter hereof and (ii) is not
intended to confer upon any Person other than the parties hereto any rights or
remedies hereunder.

                  (d) Severability. If any term or other provision of this
Agreement is invalid, illegal or incapable of being enforced by any rule of law
or public policy, all other conditions and provisions of this Agreement shall
nevertheless remain in full force and effect so long as the economic or 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 transactions contemplated hereby are fulfilled to the extent
possible.

                  (e) Governing Law. This Agreement shall be governed by, and
construed in accordance with, the Laws of the State of Delaware, regardless of
the Applicable Laws that might otherwise govern under applicable principles of
conflicts of law. All actions and proceedings arising out of or relating to this
Agreement shall be exclusively heard and determined in any state or federal
court sitting in the city of Wilmington, Delaware.

                  (f) Descriptive Headings. The descriptive headings contained
herein are for convenience of reference only and shall not affect in any way the
meaning or interpretation of this Agreement.

                  (g) Notices. All notices and other communications hereunder
shall be in writing and shall be deemed given if delivered personally,
telecopied (with confirmation) or


                                       8
<PAGE>   9


mailed by registered or certified mail (return receipt requested) to the parties
at the following addresses or sent by electronic transmission to the telecopier
number specified below:

                              If to UPR to:

                                    Union Pacific Resources Group Inc.
                                    UPR Plaza
                                    777 Main Street
                                    Fort Worth, Texas
                                    Attention: Kerry R. Brittain, Esq.
                                    Telecopy No.:  (817) 321-7026

                              with a copy to:

                                    Howard L. Shecter, Esq.
                                    Morgan Lewis & Bockius LLP
                                    101 Park Avenue
                                    New York, New York 10178
                                    Telecopy No.: (212) 309-6273

                              If to Grantee to:

                                    Anadarko Petroleum Corporation
                                    17001 Northchase Drive
                                    Houston, Texas  77060
                                    Attention:   J. Stephen Martin, Esq.
                                    Telecopy No.: (281) 874-3296

                              with a copy to:

                                    Daniel A. Neff, Esq.
                                    David A. Katz, Esq.
                                    Wachtell, Lipton, Rosen & Katz
                                    51 West 52nd Street
                                    New York, New York 10019
                                    Facsimile:   (212) 403-2000

                  (h) Counterparts. This Agreement and any amendments hereto may
be executed in counterparts, each of which shall be deemed an original and all
of which taken together shall constitute but a single document.

                  (i) Assignment. Neither this Agreement nor any of the rights,
interests or obligations hereunder or under the UPR Stock Option shall be sold,
assigned or otherwise disposed of or transferred by either of the parties hereto
(whether by operation of law or otherwise) without the prior written consent of
the other party, except that the Grantee may assign this Agreement to a wholly
owned subsidiary of the Grantee; provided, however, that no such assignment
shall have the effect of releasing the Grantee from its obligations hereunder.


                                       9
<PAGE>   10


Subject to the preceding sentence, this Agreement shall be binding upon, inure
to the benefit of and be enforceable by the parties and their respective
successors and assigns.

                  (j) Further Assurances. In the event of any exercise of the
UPR Stock Option by the Grantee, UPR and the Grantee shall execute and deliver
all other documents and instruments and take all other action that may be
reasonably necessary in order to consummate the transactions provided for by
such exercise.

                  (k) Specific Performance. The parties hereto hereby
acknowledge and agree that the failure of any party to this Agreement to perform
its agreements and covenants hereunder will cause irreparable injury to the
other party to this Agreement for which damages, even if available, will not be
an adequate remedy. Accordingly, each of the parties hereto hereby consents to
the granting of equitable relief (including specific performance and injunctive
relief) by any court of competent jurisdiction to enforce any party's
obligations hereunder. The parties further agree to waive any requirement for
the securing or posting of any bond in connection with the obtaining of any such
equitable relief and that this provision is without prejudice to any other
rights that the parties hereto may have for any failure to perform this
Agreement.









                                       10
<PAGE>   11


                  IN WITNESS WHEREOF, UPR and the Grantee have caused this UPR
Stock Option Agreement to be signed by their respective officers thereunto duly
authorized, all as of the day and year first written above.

                              ANADARKO PETROLEUM CORPORATION


                              By: /s/ Robert J. Allison, Jr.
                                  ----------------------------------------------
                                  Name:    Robert J. Allison, Jr.
                                  Title:   Chairman and Chief Executive
                                           Officer


                              UNION PACIFIC RESOURCES GROUP INC.


                              By: /s/ George Lindahl, III
                                  ----------------------------------------------
                                  Name:    George Lindahl, III
                                  Title:   Chairman, President and Chief
                                           Executive Officer



<PAGE>   12


                                                                         ANNEX A


                            SCHEDULE OF DEFINED TERMS

                  The following terms when used in the Stock Option Agreement
shall have the meanings set forth below unless the context shall otherwise
require:

                  "Agreement" shall mean this Stock Option Agreement.

                  "Applicable Price" means the highest of (i) the highest
purchase price per share paid pursuant to a third party's tender or exchange
offer made for shares of UPR Common Stock after the date hereof and on or prior
to the Put Date, (ii) the price per share to be paid by any third Person for
shares of UPR Common Stock pursuant to an agreement for a UPR Acquisition
entered into on or prior to the Put Date, and (iii) the Current Market Price. If
the consideration to be offered, paid or received pursuant to either of the
foregoing clauses (i) or (ii) shall be other than in cash, the value of such
consideration shall be determined in good faith by an independent nationally
recognized investment banking firm jointly selected by the Grantee and UPR,
which determination shall be conclusive for all purposes of this Agreement.

                  "Authorization" shall mean any and all permits, licenses,
authorizations, orders, certificates, registrations or other approvals granted
by any Governmental Authority.

                  "Beneficial Ownership," "Beneficial Owner" and "Beneficially
Own" shall have the meanings ascribed to them in Rule 13d-3 under the Exchange
Act.

                  "Business Day" shall mean a day other than Saturday, Sunday or
a federal holiday.

                  "Call Consideration" shall have the meaning ascribed to such
term in Section 6 herein.

                  "Call Date" shall have the meaning ascribed to such term in
Section 6 herein.

                  "Call Period" shall have the meaning ascribed to such term in
Section 6 herein.

                  "Closing" shall have the meaning ascribed to such term in
Section 2 herein.

                  "Closing Date" shall have the meaning ascribed to such term in
Section 2 herein.

                  "Current Market Price" shall mean, as of any date, the average
of the closing prices (or, if such securities should not trade on any trading
day, the average of the bid and asked prices therefor on such day) of UPR Common
Stock as reported on the New York Stock Exchange Composite Tape during the ten
consecutive trading days ending on (and including) the trading day immediately
prior to such date or, if the shares of UPR Common Stock are not quoted thereon,
on The Nasdaq Stock Market or, if the shares of UPR Common Stock are not quoted
thereon, on the principal trading market (as defined in Regulation M under the
Exchange Act) on which such shares are traded as reported by a recognized source
during such ten Business Day period.


                                      A-1
<PAGE>   13


                  "Exercise Event" shall mean any of the events giving rise to
the obligation of UPR to pay the $25 million fee under Section 7.5(a) of the
Merger Agreement.

                  "Exercise Notice" shall have the meaning ascribed to such term
in Section 2 herein.

                  "Exercise Price" shall have the meaning ascribed to such term
in Section 2 herein.

                  "Lien" shall mean any mortgage, pledge, security interest,
adverse claim, encumbrance, lien or charge of any kind (including any agreement
to give any of the foregoing), any conditional sale or other title retention
agreement, any lease in the nature thereof or the filing of or agreement to give
any financing statement under the Applicable Laws of any jurisdiction.

                  "Merger Agreement" shall mean that certain Agreement and Plan
of Merger dated as of the date hereof among Anadarko Petroleum Corporation, a
Delaware corporation, Dakota Merger Corp., a Utah corporation, and Union Pacific
Resources Group Inc., a Utah corporation.

                  "Notice Date" shall have the meaning ascribed to such term in
Section 2 herein.

                  "Notional Total Profit" shall mean, with respect to any number
of UPR Stock Option Shares as to which the Grantee may propose to exercise the
UPR Stock Option, the Total Profit determined as of the date of the Exercise
Notice assuming that the UPR Stock Option were exercised on such date for such
number of UPR Stock Option Shares and assuming such UPR Stock Option Shares,
together with all other UPR Stock Option Shares held by the Grantee and its
Affiliates as of such date, were sold for cash at the closing market price for
UPR Common Stock as of the close of business on the preceding trading day (less
customary brokerage commissions) and including all amounts theretofore received
or concurrently being paid to the Grantee pursuant to clauses (i), (ii) and
(iii) of the definition of Total Profit.

                  "Offeror's Notice" shall have the meaning ascribed to such
term in Section 8 herein.

                  "Person" shall have the meaning specified in Sections 3(a)(9)
and 13(d)(3) of the Exchange Act.

                  "Profit Cap" shall mean $25 million, unless the conditions to
the payment by UPR of the additional $100 million fee under Section 7.5(a) of
the Merger Agreement shall have occurred, in which case "Profit Cap" shall mean
$125 million.

                  "Put Consideration" shall have the meaning ascribed to such
term in Section 5 herein.

                  "Put Date" shall have the meaning ascribed to such term in
Section 5 herein.

                  "Put Period" shall have the meaning ascribed to such term in
Section 5 herein.

                  "Put Right" shall have the meaning ascribed to such term in
Section 5 herein.


                                      A-2
<PAGE>   14


                  "Registration Expenses" shall mean the expenses associated
with the preparation and filing of any registration statement pursuant to
Section 7 herein and any sale covered thereby (including any fees related to
blue sky qualifications and filing fees in respect of the National Association
of Securities Dealers, Inc.), but excluding underwriting discounts or
commissions or brokers' fees in respect to shares to be sold by the Grantee and
the fees and disbursements of the Grantee's counsel.

                  "Registration Period" shall mean, subject to Section 4 hereof,
the period of two years following the first exercise of the UPR Stock Option by
the Grantee.

                  "Subcorp" shall mean Dakota Merger Corp., a Utah corporation
and a wholly owned subsidiary of Grantee.

                  "Total Profit" shall mean the aggregate (before income taxes)
of the following: (i) all amounts received by the Grantee or concurrently being
paid to the Grantee pursuant to Section 5 for the repurchase of all or part of
the unexercised portion of the UPR Stock Option, (ii) (A) the amounts received
by the Grantee or concurrently being paid to the Grantee pursuant to the sale of
UPR Stock Option Shares (or any other securities into which such UPR Stock
Option Shares are converted or exchanged), including sales made to UPR or
pursuant to a registration statement under the Securities Act or any exemption
therefrom, less (B) the Grantee's purchase price for such UPR Stock Option
Shares and (iii) all amounts received by the Grantee from UPR or concurrently
being paid to the Grantee pursuant to Section 7.5(a) of the Merger Agreement.

                  "Unexercised UPR Stock Option Shares" shall mean, from and
after the Exercise Date until the expiration of the UPR Stock Option Term, those
UPR Stock Option Shares as to which the UPR Stock Option remains unexercised
from time to time.

                  "UPR Stock Option" shall mean the UPR Stock Option granted by
UPR to Grantee pursuant to Section 2 herein.

                  "UPR Stock Option Shares" shall have the meaning ascribed to
such term in Section 2 herein.

                  "UPR Stock Option Term" shall have the meaning ascribed to
such term in Section 2 herein.



                                      A-3

<PAGE>   1
                                                                     EXHIBIT 2.3


                                                                  CONFORMED COPY



                                    ANADARKO
                             STOCK OPTION AGREEMENT


                  This STOCK OPTION AGREEMENT dated as of April 2, 2000 is by
and between Anadarko Petroleum Corporation, a Delaware corporation ("Anadarko"),
and Union Pacific Resources Group Inc., a Utah corporation (the "Grantee").

                                    RECITALS

                  The Grantee, Anadarko and Subcorp propose to enter into the
Merger Agreement providing, among other things, for the Merger pursuant to the
Merger Agreement of Subcorp with and into the Grantee which shall be the
surviving corporation.

                  As a condition and inducement to the Grantee's willingness to
enter into the Merger Agreement, the Grantee has requested that Anadarko agree,
and Anadarko has agreed, to grant the Grantee the Anadarko Stock Option.

                  As a condition and inducement to Anadarko's willingness to
enter into the Merger Agreement, Anadarko has separately requested that the
Grantee agree, and the Grantee has agreed, to grant Anadarko the UPR Stock
Option pursuant to a Stock Option Agreement dated as of April 2, 2000 by and
between the Grantee and Anadarko.

                  The Board of Directors of the Grantee has approved the Merger
Agreement, the Merger and this Agreement and has recommended approval of the
Merger Agreement by the holders of UPR Common Stock.

                  The Board of Directors of Anadarko has approved the Merger
Agreement, the Merger and this Agreement and has recommended approval of the
issuance of Anadarko Common Shares pursuant to the Merger Agreement by the
holders of Anadarko Common Shares.

                  NOW, THEREFORE, in consideration of the foregoing and the
respective representations, warranties, covenants and agreements set forth
herein and in the Merger Agreement, Anadarko and the Grantee agree as follows:

                  1. Capitalized Terms. Those capitalized terms used but not
defined herein that are defined in the Merger Agreement are used herein with the
same meanings as ascribed to them therein. Those capitalized terms used in this
Agreement that are not defined in the Merger Agreement or in this Agreement are
defined in Annex A hereto and are used herein with the meanings ascribed to them
therein.

                  2. The Anadarko Stock Option.

                  (a) Grant of Anadarko Stock Option. Subject to the terms and
conditions set forth herein, Anadarko hereby grants to the Grantee an
irrevocable option to purchase, out of the authorized but unissued Anadarko
Common Shares, 25,886,726 shares of Anadarko Common


<PAGE>   2


Shares (as adjusted as set forth herein) (the "Anadarko Stock Option Shares"),
at the Exercise Price.

                  (b) Exercise Price. The exercise price (the "Exercise Price")
of the Anadarko Stock Option shall be $38.6875 per Anadarko Stock Option Share.

                  (c) Term. The Anadarko Stock Option shall be exercisable at
any time and from time to time following the occurrence of an Exercise Event and
shall remain in full force and effect until the earliest to occur of (i) the
Effective Time, (ii) the first anniversary of the receipt by Grantee of written
notice from Anadarko of the occurrence of an Exercise Event and (iii)
termination of the Merger Agreement in accordance with its terms prior to the
occurrence of an Exercise Event unless such termination itself constitutes an
Exercise Event (the "Anadarko Stock Option Term"). If the Anadarko Stock Option
is not theretofore exercised, the rights and obligations set forth in this
Agreement shall terminate at the expiration of the Anadarko Stock Option Term.

                  (d) Exercise of Anadarko Stock Option.

                  (i) The Grantee may exercise the Anadarko Stock Option, in
whole or in part, at any time and from time to time during the Anadarko Stock
Option Term. Notwithstanding the expiration of the Anadarko Stock Option Term,
the Grantee shall be entitled to purchase those Anadarko Stock Option Shares
with respect to which it has exercised the Anadarko Stock Option in accordance
with the terms hereof prior to the expiration of the Anadarko Stock Option Term.

                  (ii) If the Grantee wishes to exercise the Anadarko Stock
Option, it shall send a written notice (an "Exercise Notice") (the date of which
being herein referred to as the "Notice Date") to Anadarko specifying (i) the
total number of Anadarko Stock Option Shares it intends to purchase pursuant to
such exercise and (ii) a place and a date (the "Closing Date") not earlier than
three Business Days nor later than 15 Business Days from the Notice Date for the
closing of the purchase and sale pursuant to the Anadarko Stock Option (the
"Closing").

                  (iii) If the Closing cannot be effected by reason of the
application of any Applicable Law, the Closing Date shall be extended to the
tenth Business Day following the expiration or termination of the restriction
imposed by such Applicable Law. Without limiting the foregoing, if prior
notification to, or Authorization of, any Governmental Authority is required in
connection with the purchase of such Anadarko Stock Option Shares by virtue of
the application of such Applicable Law, the Grantee and, if applicable, Anadarko
shall promptly file the required notice or application for Authorization and the
Grantee, with the cooperation of Anadarko, shall expeditiously process the same.

                  (iv) Notwithstanding Section 2(d)(iii), if the Closing Date
shall not have occurred within nine months after the related Notice Date as a
result of one or more restrictions imposed by the application of any Applicable
Law, the exercise of the Anadarko Stock Option effected on the Notice Date shall
be deemed to have expired.


                                       2
<PAGE>   3


                  (e) Payment and Delivery of Certificates.

                  (i) At each Closing, the Grantee shall pay to Anadarko in
immediately available funds by wire transfer to a bank account designated by
Anadarko an amount equal to the Exercise Price multiplied by the number of
Anadarko Stock Option Shares to be purchased on such Closing Date.

                  (ii) At each Closing, simultaneously with the delivery of
immediately available funds as provided above, Anadarko shall deliver to the
Grantee a certificate or certificates representing the Anadarko Stock Option
Shares to be purchased at such Closing, which Anadarko Stock Option Shares shall
be duly authorized, validly issued, fully paid and nonassessable and free and
clear of all Liens, and the Grantee shall deliver to Anadarko its written
agreement that the Grantee will not offer to sell or otherwise dispose of such
Anadarko Stock Option Shares in violation of applicable Law or the provisions of
this Agreement.

                  (f) Certificates. Certificates for the Anadarko Stock Option
Shares delivered at each Closing shall be endorsed with a restrictive legend
that shall read substantially as follows:

                  THE TRANSFER OF THE STOCK REPRESENTED BY THIS CERTIFICATE IS
         SUBJECT TO RESTRICTIONS ARISING UNDER THE SECURITIES ACT OF 1933, AS
         AMENDED, AND PURSUANT TO THE TERMS OF A STOCK OPTION AGREEMENT DATED AS
         OF APRIL 2, 2000. A COPY OF SUCH AGREEMENT WILL BE PROVIDED TO THE
         HOLDER HEREOF WITHOUT CHARGE UPON RECEIPT BY ANADARKO OF A WRITTEN
         REQUEST THEREFOR.

A new certificate or certificates evidencing the same number of Anadarko Common
Shares will be issued to the Grantee in lieu of the certificate bearing the
above legend, and such new certificate shall not bear such legend, insofar as it
applies to the Securities Act, if the Grantee shall have delivered to Anadarko a
copy of a letter from the staff of the Commission, or an opinion of counsel in
form and substance reasonably satisfactory to Anadarko and its counsel, to the
effect that such legend is not required for purposes of the Securities Act.

                  (g) If at the time of issuance of any Anadarko Common Shares
pursuant to any exercise of the Anadarko Stock Option, Anadarko shall have
issued any share purchase rights or similar securities to holders of Anadarko
Common Shares, then each Anadarko Stock Option Share purchased pursuant to the
Anadarko Stock Option shall also include rights with terms substantially the
same as and at least as favorable to the Grantee as those issued to other
holders of Anadarko Common Shares.

                  3. Adjustment Upon Changes in Capitalization, Etc.

                  (a) In the event of any change in Anadarko Common Shares by
reason of a stock dividend, split-up, combination, recapitalization, exchange of
shares or similar transaction, the type and number of shares or securities
subject to the Anadarko Stock Option, and the Exercise Price therefor, shall be
adjusted appropriately, and proper provision shall be made in the agreements
governing such transaction, so that the Grantee shall receive upon exercise of
the


                                       3
<PAGE>   4


Anadarko Stock Option the same class and number of outstanding shares or other
securities or property that Grantee would have received in respect of Anadarko
Common Shares if the Anadarko Stock Option had been exercised immediately prior
to such event, or the record date therefor, as applicable.

                  (b) If any additional Anadarko Common Shares are issued after
the date of this Agreement (other than pursuant to an event described Section
3(a) above), the number of Anadarko Common Shares then remaining subject to the
Anadarko Stock Option shall be adjusted so that, after such issuance of
additional shares, such number of shares then remaining subject to the Anadarko
Stock Option, together with shares theretofore issued pursuant to the Anadarko
Stock Option, equals 19.9% of the number of Anadarko Common Shares then issued
and outstanding.

                  (c) To the extent any of the provisions of this Agreement
apply to the Exercise Price, they shall be deemed to refer to the Exercise Price
as adjusted pursuant to this Section 3.

                  4. Retention of Beneficial Ownership. To the extent that the
Grantee shall exercise the Anadarko Stock Option, the Grantee shall, unless the
Grantee shall exercise the Put Right or Anadarko shall exercise the Call Right,
retain sole ownership of the Anadarko Common Shares so acquired through the end
of the Call Period.

                  5. Repurchase at the Option of Grantee.

                  (a) At the request of the Grantee made at any time and from
time to time after the occurrence of an Exercise Event and prior to the earlier
of (i) 120 days after the expiration of the Anadarko Stock Option Term and (ii)
120 days after the conditions to the payment by Anadarko of the additional $100
million fee under Section 7.5(b) of the Merger Agreement shall have occurred
(the "Put Period"), Anadarko (or any successor thereto) shall, at the election
of the Grantee (the "Put Right"), repurchase from the Grantee (i) that portion
of the Anadarko Stock Option relating to all or any part of the Unexercised
Anadarko Stock Option Shares (or as to which the Anadarko Stock Option has been
exercised but the Closing has not occurred) and (ii) all or any portion of the
Anadarko Stock Option Shares purchased by the Grantee pursuant hereto and with
respect to which the Grantee then has ownership. The date on which the Grantee
exercises its rights under this Section 5 is referred to as the "Put Date." Such
repurchase shall be at an aggregate price (the "Put Consideration") equal to the
sum of:

                           (i) the aggregate Exercise Price paid by the Grantee
                  for any Anadarko Stock Option Shares which the Grantee owns
                  and as to which the Grantee is exercising the Put Right;

                           (ii) the excess, if any, of the Applicable Price over
                  the Exercise Price paid by the Grantee for each Anadarko Stock
                  Option Share as to which the Grantee is exercising the Put
                  Right multiplied by the number of such shares; and

                           (iii) the excess, if any, of (x) the Applicable Price
                  per share of Anadarko Common Shares over (y) the Exercise
                  Price multiplied by the number


                                       4
<PAGE>   5


                  of Unexercised Anadarko Stock Option Shares as to which the
                  Grantee is exercising the Put Right.

                  (b) If the Grantee exercises its rights under this Section 5,
Anadarko shall, within five Business Days after the Put Date, pay the Put
Consideration to the Grantee in immediately available funds, and the Grantee
shall surrender to Anadarko the Anadarko Stock Option or portion of the Anadarko
Stock Option and the certificates evidencing the Anadarko Stock Option Shares
purchased thereunder. The Grantee shall warrant to Anadarko that, immediately
prior to the repurchase thereof pursuant to this Section 5, the Grantee had sole
record and Beneficial Ownership of the Anadarko Stock Option or such shares, or
both, as the case may be, and that the Anadarko Stock Option or such shares, or
both, as the case may be, were then held free and clear of all Liens.

                  (c) If the Anadarko Stock Option has been exercised, in whole
or in part, as to any Anadarko Stock Option Shares subject to the Put Right but
the Closing thereunder has not occurred, the payment of the Put Consideration
shall, to that extent, render such exercise null and void.

                  (d) Notwithstanding any provision to the contrary in this
Agreement, the Grantee may not exercise its rights pursuant to this Section 5 in
a manner that would result in Total Profit of more than the Profit Cap;
provided, however, that nothing in this sentence shall limit the Grantee's
ability to exercise the Anadarko Stock Option in accordance with its terms.

                  6. Repurchase at the Option of Anadarko.

                  (a) To the extent the Grantee shall not have previously
exercised its rights under Section 5, at the request of Anadarko made at any
time during the 120-day period commencing at the expiration of the Put Period
(the "Call Period"), Anadarko may repurchase from the Grantee, and the Grantee
shall sell, or cause to be sold, to Anadarko , all (but not less than all) of
the Anadarko Common Shares acquired by the Grantee pursuant hereto and with
respect to which the Grantee has ownership at the time of such repurchase at a
price per share equal to the greater of (A) the Current Market Price and (B) the
Exercise Price per share in respect of the shares so acquired (such price per
share multiplied by the number of Anadarko Common Shares to be repurchased
pursuant to this Section 6 being herein called the "Call Consideration"). The
date on which Anadarko exercises its rights under this Section 6 is referred to
as the "Call Date."

                  (b) If Anadarko exercises its rights under this Section 6,
Anadarko shall, within five Business Days pay the Call Consideration in
immediately available funds, and the Grantee shall surrender to Anadarko
certificates evidencing the Anadarko Common Shares purchased hereunder, and the
Grantee shall warrant to Anadarko that, immediately prior to the repurchase
thereof pursuant to this Section 6, the Grantee had sole record and Beneficial
Ownership of such shares and that such shares were then held free and clear of
all Liens.

                  7. Registration Rights.

                  (a) Anadarko shall, if requested by the Grantee at any time
and from time to time during the Registration Period, as expeditiously as
practicable, prepare, file and cause to be


                                       5
<PAGE>   6


made effective up to two registration statements under the Securities Act if
such registration is required in order to permit the offering, sale and delivery
of any or all Anadarko Common Shares or other securities that have been acquired
by or are issuable to the Grantee upon exercise of the Anadarko Stock Option in
accordance with the intended method of sale or other disposition stated by the
Grantee, including, at the sole discretion of Anadarko, a "shelf" registration
statement under Rule 415 under the Securities Act or any successor provision,
and Anadarko shall use all reasonable efforts to qualify such shares or other
securities under any applicable state securities laws. Anadarko shall use all
reasonable efforts to cause each such registration statement to become
effective, to obtain all consents or waivers of other parties that are required
therefor and to keep such registration statement effective for such period not
in excess of 180 days from the day such registration statement first becomes
effective as may be reasonably necessary to effect such sale or other
disposition. The obligations of Anadarko hereunder to file a registration
statement and to maintain its effectiveness may be suspended for one or more
periods of time not exceeding 60 days in the aggregate if the Board of Directors
of Anadarko shall have determined in good faith that the filing of such
registration or the maintenance of its effectiveness would require disclosure of
nonpublic information that would materially and adversely affect Anadarko. For
purposes of determining whether two requests have been made under this Section
7, only requests relating to a registration statement that has become effective
under the Securities Act and pursuant to which the Grantee has disposed of all
shares covered thereby in the manner contemplated therein shall be counted.
Notwithstanding any other provision of this Section 7, any request for
registration shall permit Anadarko, upon notice given within 20 days of the
request for registration, to repurchase from the Grantee any shares as to which
the Grantee requests registration at a price per share equal to the Current
Market Price at the date Anadarko notifies the Grantee of its decision to so
repurchase.

                  (b) The Registration Expenses shall be for the account of
Anadarko; provided, however, that Anadarko shall not be required to pay any
Registration Expenses with respect to such registration if the registration
request is subsequently withdrawn at the request of the Grantee unless the
Grantee agrees to forfeit its right to request one registration.

                  (c) The Grantee shall provide all information reasonably
requested by Anadarko for inclusion in any registration statement to be filed
hereunder. If during the Registration Period Anadarko shall propose to register
under the Securities Act the offering, sale and delivery of Anadarko Common
Shares for cash for its own account or for any other stockholder of Anadarko
pursuant to a firm underwriting, it shall, in addition to Anadarko's other
obligations under this Section 7, allow the Grantee the right to participate in
such registration provided that the Grantee participates in the underwriting;
provided, however, that, if the managing underwriter of such offering advises
Anadarko in writing that in its opinion the number of Anadarko Common Shares
requested to be included in such registration exceeds the number that can be
sold in such offering, Anadarko shall, after fully including therein all
securities to be sold by Anadarko, include the shares requested to be included
therein by Grantee pro rata (based on the number of shares intended to be
included therein) with the shares intended to be included therein by Persons
other than Anadarko.

                  (d) In connection with any offering, sale and delivery of
Anadarko Common Shares pursuant to a registration statement effected pursuant to
this Section 7, Anadarko and the Grantee shall provide each other and each
underwriter of the offering with customary


                                       6
<PAGE>   7


representations, warranties and covenants, including covenants of
indemnification and contribution.

                  8. First Refusal. Subject to the provisions of Sections 5 and
6 herein, at any time after the first occurrence of an Exercise Event and prior
to the second anniversary of the first purchase of shares of Anadarko Common
Shares pursuant to the Anadarko Stock Option, if the Grantee shall desire to
sell, assign, transfer or otherwise dispose of all or any of the Anadarko Stock
Option Shares or other securities acquired by it pursuant to the Anadarko Stock
Option, it shall give Anadarko written notice of the proposed transaction (an
"Offeror's Notice"), identifying the proposed transferee, accompanied by a copy
of a binding offer to purchase such shares or other securities signed by such
transferee and setting forth the terms of the proposed transaction. An Offeror's
Notice shall be deemed an offer by the Grantee to Anadarko, which may be
accepted, in whole but not in part, within 20 Business Days of the receipt of
such Offeror's Notice, on the same terms and conditions and at the same price at
which the Grantee is proposing to transfer such shares or other securities to
such transferee. The purchase of any such shares or other securities by Anadarko
shall be settled within 20 Business Days of the date of the acceptance of the
offer and the purchase price shall be paid to the Grantee in immediately
available funds. If Anadarko shall fail or refuse to purchase all the shares or
other securities covered by an Offeror's Notice, the Grantee may, within 60 days
from the date of the Offeror's Notice, sell all, but not less than all, of such
shares or other securities to the proposed transferee at no less than the price
specified and on terms no more favorable than those set forth in the Offeror's
Notice; provided, however, that the provisions of this sentence shall not limit
the rights the Grantee may otherwise have if Anadarko has accepted the offer
contained in the Offeror's Notice and wrongfully refuses to purchase the shares
or other securities subject thereto. The requirements of this Section 8 shall
not apply to (a) any disposition as a result of which the proposed transferee
would own beneficially not more than 2% of the outstanding voting power of
Anadarko, (b) any disposition of Anadarko Common Shares or other securities by a
Person to whom the Grantee has assigned its rights under the Anadarko Stock
Option with the consent of Anadarko, (c) any sale by means of a public offering
registered under the Securities Act or (d) any transfer to a wholly owned
subsidiary of the Grantee which agrees in writing to be bound by the terms
hereof.

                  9. Profit Limitation.

                  (a) Notwithstanding any other provision of this Agreement, in
no event shall the Grantee's Total Profit exceed the Profit Cap and, if it
otherwise would exceed such amount, the Grantee, at its sole election, shall
either (i) deliver to Anadarko for cancellation Anadarko Stock Option Shares
previously purchased by Grantee, (ii) pay cash or other consideration to
Anadarko, (iii) reduce the amount of the fee payable to Grantee under Section
7.5(b) of the Merger Agreement or (iv) undertake any combination thereof, so
that the Grantee's Total Profit shall not exceed the Profit Cap after taking
into account the foregoing actions.

                  (b) Notwithstanding any other provision of this Agreement,
this Anadarko Stock Option may not be exercised for a number of Anadarko Stock
Option Shares that would, as of the Notice Date, result in a Notional Total
Profit of more than the Profit Cap, and, if exercise of the Anadarko Stock
Option otherwise would exceed the Profit Cap, the Grantee, at its sole option,
may increase the Exercise Price for that number of Anadarko Stock Option Shares


                                       7
<PAGE>   8


set forth in the Exercise Notice so that the Notional Total Profit shall not
exceed the Profit Cap; provided, however, that nothing in this sentence shall
restrict any exercise of the Anadarko Stock Option otherwise permitted by this
Section 9(b) on any subsequent date at the Exercise Price set forth in Section
2(b) if such exercise would not then be restricted under this Section 9(b).

                  10. Listing. If Anadarko Common Shares or any other securities
then subject to the Anadarko Stock Option are then listed on the NYSE, Anadarko,
upon the occurrence of an Exercise Event, will promptly file an application to
list on the NYSE the Anadarko Common Shares or other securities then subject to
the Anadarko Stock Option and will use all reasonable efforts to cause such
listing application to be approved as promptly as practicable.

                  11. Replacement of Agreement. Upon receipt by Anadarko of
evidence reasonably satisfactory to it of the loss, theft, destruction or
mutilation of this Agreement, and (in the case of loss, theft or destruction) of
reasonably satisfactory indemnification, and upon surrender and cancellation of
this Agreement, if mutilated, Anadarko will execute and deliver a new Agreement
of like tenor and date. Any such new Agreement shall constitute an additional
contractual obligation of Anadarko, whether or not the Agreement so lost,
stolen, destroyed or mutilated shall at any time be enforceable by anyone.

                  12. Miscellaneous.

                  (a) Expenses. Except as otherwise provided in the Merger
Agreement or as otherwise expressly provided herein, each of the parties hereto
shall bear and pay all costs and expenses incurred by it or on its behalf in
connection with the transactions contemplated hereunder, including fees and
expenses of its own financial consultants, investment bankers, accountants and
counsel.

                  (b) Waiver and Amendment. Any provision of this Agreement may
be waived at any time by the party that is entitled to the benefits of such
provision. This Agreement may not be modified, amended, altered or supplemented
except upon the execution and delivery of a written agreement executed by the
parties hereto.

                  (c) Entire Agreement; No Third Party Beneficiary;
Severability. Except as otherwise set forth in the Merger Agreement, this
Agreement (including the Merger Agreement and the other documents and
instruments referred to herein and therein) (i) constitutes the entire agreement
and supersedes all prior agreements and understandings, both written and oral,
between the parties with respect to the subject matter hereof and (ii) is not
intended to confer upon any Person other than the parties hereto any rights or
remedies hereunder.

                  (d) Severability. If any term or other provision of this
Agreement is invalid, illegal or incapable of being enforced by any rule of law
or public policy, all other conditions and provisions of this Agreement shall
nevertheless remain in full force and effect so long as the economic or 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


                                       8
<PAGE>   9


possible in an acceptable manner to the end that transactions contemplated
hereby are fulfilled to the extent possible.

                  (e) Governing Law. This Agreement shall be governed by, and
construed in accordance with, the Laws of the State of Delaware, regardless of
the Applicable Laws that might otherwise govern under applicable principles of
conflicts of law. All actions and proceedings arising out of or relating to this
Agreement shall be exclusively heard and determined in any state or federal
court sitting in the city of Wilmington, Delaware.

                  (f) Descriptive Headings. The descriptive headings contained
herein are for convenience of reference only and shall not affect in any way the
meaning or interpretation of this Agreement.

                  (g) Notices. All notices and other communications hereunder
shall be in writing and shall be deemed given if delivered personally,
telecopied (with confirmation) or mailed by registered or certified mail (return
receipt requested) to the parties at the following addresses or sent by
electronic transmission to the telecopier number specified below:

                        If to Anadarko to:

                              Anadarko Petroleum Corporation
                              17001 Northchase Drive
                              Houston, Texas  77060
                              Attention:  J. Stephen Martin, Esq.
                    `         Telecopy No.: (281) 874-3296

                        with a copy to:

                              Daniel A. Neff, Esq.
                              David A. Katz, Esq.
                              Wachtell, Lipton, Rosen & Katz
                              51 West 52nd Street
                              New York, New York  10019
                              Telecopy No.:  (212) 403-2000

                        If to Grantee to:

                              Union Pacific Resources Group Inc.
                              UPR Plaza
                              777 Main Street
                              Fort Worth, Texas
                              Attention: Kerry R. Brittain, Esq.
                              Telecopy No.:  (817) 321-7026


                                       9
<PAGE>   10


                        with a copy to:

                              Howard L. Shecter, Esq.
                              Morgan Lewis & Bockius LLP
                              101 Park Avenue
                              New York, New York 10178
                              Telecopy No.: (212) 309-6273




                  (h) Counterparts. This Agreement and any amendments hereto may
be executed in counterparts, each of which shall be deemed an original and all
of which taken together shall constitute but a single document.

                  (i) Assignment. Neither this Agreement nor any of the rights,
interests or obligations hereunder or under the Anadarko Stock Option shall be
sold, assigned or otherwise disposed of or transferred by either of the parties
hereto (whether by operation of law or otherwise) without the prior written
consent of the other party, except that the Grantee may assign this Agreement to
a wholly owned subsidiary of the Grantee; provided, however, that no such
assignment shall have the effect of releasing the Grantee from its obligations
hereunder. Subject to the preceding sentence, this Agreement shall be binding
upon, inure to the benefit of and be enforceable by the parties and their
respective successors and assigns.

                  (j) Further Assurances. In the event of any exercise of the
Anadarko Stock Option by the Grantee, Anadarko and the Grantee shall execute and
deliver all other documents and instruments and take all other action that may
be reasonably necessary in order to consummate the transactions provided for by
such exercise.

                  (k) Specific Performance. The parties hereto hereby
acknowledge and agree that the failure of any party to this Agreement to perform
its agreements and covenants hereunder will cause irreparable injury to the
other party to this Agreement for which damages, even if available, will not be
an adequate remedy. Accordingly, each of the parties hereto hereby consents to
the granting of equitable relief (including specific performance and injunctive
relief) by any court of competent jurisdiction to enforce any party's
obligations hereunder. The parties further agree to waive any requirement for
the securing or posting of any bond in connection with the obtaining of any such
equitable relief and that this provision is without prejudice to any other
rights that the parties hereto may have for any failure to perform this
Agreement.



                                       10
<PAGE>   11


                  IN WITNESS WHEREOF, Anadarko and the Grantee have caused this
Anadarko Stock Option Agreement to be signed by their respective officers
thereunto duly authorized, all as of the day and year first written above.

                                 ANADARKO PETROLEUM CORPORATION


                                 By: /s/ Robert J. Allison, Jr.
                                     -------------------------------------------
                                     Name:    Robert J. Allison, Jr.
                                     Title:   Chairman and Chief Executive
                                              Officer


                                 UNION PACIFIC RESOURCES GROUP INC.


                                 By: /s/ George Lindahl, III
                                     -------------------------------------------
                                     Name:    George Lindahl, III
                                     Title:   Chairman, President and Chief
                                              Executive Officer



<PAGE>   12


                                                                         ANNEX A


                            SCHEDULE OF DEFINED TERMS

                  The following terms when used in the Stock Option Agreement
shall have the meanings set forth below unless the context shall otherwise
require:

                  "Agreement" shall mean this Stock Option Agreement.

                  "Anadarko Stock Option" shall mean the option granted by
Anadarko to Grantee pursuant to Section 2 herein.

                  "Anadarko Stock Option Shares" shall have the meaning ascribed
to such term in Section 2 herein.

                  "Anadarko Stock Option Term" shall have the meaning ascribed
to such term in Section 2 herein.

                  "Applicable Price" means the highest of (i) the highest
purchase price per share paid pursuant to a third party's tender or exchange
offer made for Anadarko Common Shares after the date hereof and on or prior to
the Put Date, (ii) the price per share to be paid by any third Person for
Anadarko Common Shares pursuant to an agreement for a Anadarko Acquisition
entered into on or prior to the Put Date, and (iii) the Current Market Price. If
the consideration to be offered, paid or received pursuant to either of the
foregoing clauses (i) or (ii) shall be other than in cash, the value of such
consideration shall be determined in good faith by an independent nationally
recognized investment banking firm jointly selected by the Grantee and Anadarko,
which determination shall be conclusive for all purposes of this Agreement.

                  "Authorization" shall mean any and all permits, licenses,
authorizations, orders certificates, registrations or other approvals granted by
any Governmental Authority.

                  "Beneficial Ownership," "Beneficial Owner" and "Beneficially
Own" shall have the meanings ascribed to them in Rule 13d-3 under the Exchange
Act.

                  "Business Day" shall mean a day other than Saturday, Sunday or
a federal holiday.

                  "Call Consideration" shall have the meaning ascribed to such
term in Section 6 herein.

                  "Call Date" shall have the meaning ascribed to such term in
Section 6 herein.

                  "Call Period" shall have the meaning ascribed to such term in
Section 6 herein.

                  "Closing" shall have the meaning ascribed to such term in
Section 2 herein.

                  "Closing Date" shall have the meaning ascribed to such term in
Section 2 herein.






                                      A-1
<PAGE>   13

                  "Current Market Price" shall mean, as of any date, the average
of the closing prices (or, if such securities should not trade on any trading
day, the average of the bid and asked prices therefor on such day) of Anadarko
Common Shares as reported on the New York Stock Exchange Composite Tape during
the ten consecutive trading days ending on (and including) the trading day
immediately prior to such date or, if the Anadarko Common Shares are not quoted
thereon, on The Nasdaq Stock Market or, if the Anadarko Common Shares are not
quoted thereon, on the principal trading market (as defined in Regulation M
under the Exchange Act) on which such shares are traded as reported by a
recognized source during such ten Business Day period.

                   "Exercise Event" shall mean any of the events giving rise to
the obligation of Anadarko to pay the $25 million fee under Section 7.5(b) of
the Merger Agreement.

                  "Exercise Notice" shall have the meaning ascribed to such term
in Section 2 herein.

                  "Exercise Price" shall have the meaning ascribed to such term
in Section 2 herein.

                  "Lien" shall mean any mortgage, pledge, security interest,
adverse claim, encumbrance, lien or charge of any kind (including any agreement
to give any of the foregoing), any conditional sale or other title retention
agreement, any lease in the nature thereof or the filing of or agreement to give
any financing statement under the Applicable Laws of any jurisdiction.

                  "Merger Agreement" shall mean that certain Agreement and Plan
of Merger dated as of the date hereof among Anadarko Petroleum Corporation, a
Delaware corporation, Dakota Merger Corp., a Utah corporation, and Union Pacific
Resources Group Inc., a Utah corporation.

                  "Notice Date" shall have the meaning ascribed to such term in
Section 2 herein.

                  "Notional Total Profit" shall mean, with respect to any number
of Anadarko Stock Option Shares as to which the Grantee may propose to exercise
the Anadarko Stock Option, the Total Profit determined as of the date of the
Exercise Notice assuming that the Anadarko Stock Option were exercised on such
date for such number of Anadarko Stock Option Shares and assuming such Anadarko
Stock Option Shares, together with all other Anadarko Stock Option Shares held
by the Grantee and its Affiliates as of such date, were sold for cash at the
closing market price for Anadarko Common Shares as of the close of business on
the preceding trading day (less customary brokerage commissions) and including
all amounts theretofore received or concurrently being paid to the Grantee
pursuant to clauses (i), (ii) and (iii) of the definition of Total Profit.

                  "Offeror's Notice" shall have the meaning ascribed to such
term in Section 8 herein.

                  "Person" shall have the meaning specified in Sections 3(a)(9)
and 13(d)(3) of the Exchange Act.


                                      A-2
<PAGE>   14


                  "Profit Cap" shall mean $25 million, unless the conditions to
the payment by Anadarko of the additional $100 million fee under Section 7.5(b)
of the Merger Agreement shall have occurred, in which case "Profit Cap" shall
mean $125 million.

                  "Put Consideration" shall have the meaning ascribed to such
term in Section 5 herein.

                  "Put Date" shall have the meaning ascribed to such term in
Section 5 herein.

                  "Put Period" shall have the meaning ascribed to such term in
Section 5 herein.

                  "Put Right" shall have the meaning ascribed to such term in
Section 5 herein.

                  "Registration Expenses" shall mean the expenses associated
with the preparation and filing of any registration statement pursuant to
Section 7 herein and any sale covered thereby (including any fees related to
blue sky qualifications and filing fees in respect of the National Association
of Securities Dealers, Inc.), but excluding underwriting discounts or
commissions or brokers' fees in respect to shares to be sold by the Grantee and
the fees and disbursements of the Grantee's counsel.

                  "Registration Period" shall mean, subject to Section 4 hereof,
the period of two years following the first exercise of the Anadarko Stock
Option by the Grantee.

                  "Subcorp" shall mean Dakota Merger Corp., a Utah corporation
and a wholly owned subsidiary of Anadarko.

                  "Total Profit" shall mean the aggregate (before income taxes)
of the following: (i) all amounts received by the Grantee or concurrently being
paid to the Grantee pursuant to Section 5 for the repurchase of all or part of
the unexercised portion of the Anadarko Stock Option, (ii) (A) the amounts
received by the Grantee or concurrently being paid to the Grantee pursuant to
the sale of Anadarko Stock Option Shares (or any other securities into which
such Anadarko Stock Option Shares are converted or exchanged), including sales
made to Anadarko or pursuant to a registration statement under the Securities
Act or any exemption therefrom, less (B) the Grantee's purchase price for such
Anadarko Stock Option Shares and (iii) all amounts received by the Grantee from
Anadarko or concurrently being paid to the Grantee pursuant to Section 7.5(b) of
the Merger Agreement.

                  "Unexercised Anadarko Stock Option Shares" shall mean, from
and after the Exercise Date until the expiration of the Anadarko Stock Option
Term, those Anadarko Stock Option Shares as to which the Anadarko Stock Option
remains unexercised from time to time.




                                      A-3

<PAGE>   1
                                                                     EXHIBIT 2.4


                       AMENDMENT NO. 1 TO RIGHTS AGREEMENT

         AMENDMENT (this "Amendment"), dated as of April 2, 2000, to the Amended
and Restated Rights Agreement, dated as of December 1, 1998, between Union
Pacific Resources Group Inc., a Utah corporation (the "Company"), and Harris
Trust and Savings Bank as Rights Agent (the "Rights Agent"). Capitalized terms
used but not defined herein, unless the context otherwise requires, have the
meanings ascribed to such terms in the Rights Agreement.

         WHEREAS, the Company and the Rights Agent have heretofore executed and
entered into the Rights Agreement; and

         WHEREAS, pursuant to Section 26 of the Rights Agreement, the Company
may from time to time supplement or amend the Rights Agreement in accordance
with the provisions of Section 26 thereof; and

         WHEREAS, it is proposed that the Company enter into an Agreement and
Plan of Merger (as it may be amended or supplemented from time to time, the
"Merger Agreement"), dated April 2, 2000, among Anadarko Petroleum Corporation
("Anadarko"), Dakota Merger Corp., a Utah corporation and wholly-owned
subsidiary of Anadarko ("Subcorp"), and the Company, which provides for, among
other things, the merger of Subcorp with and into the Company (the "Merger");
and

         WHEREAS, the Merger Agreement contemplates that, concurrently with and
as a condition to the execution and delivery of the Merger Agreement, Anadarko
and the Company will enter into the Stock Option Agreement dated April 2, 2000
(the "UPR Stock Option Agreement"); and

         WHEREAS, the Merger Agreement contemplates that the Company will amend
the Rights Agreement so that Anadarko is exempt from the definition of
"Acquiring Person" contained in the Rights Agreement and no "Stock Acquisition
Date" or "Distribution Date" will occur as a result of the execution of the UPR
Stock Option Agreement or the acquisition or transfer of Common Shares by the
Company pursuant to the UPR Stock Option Agreement; and

         WHEREAS, the Board of Directors has determined that it is in the best
interests of the Company and its shareholders to amend the Rights Agreement as
contemplated by the Merger Agreement.

         NOW, THEREFORE, the Company hereby amends the Rights Agreement as
follows:

         1.       Section 1(a) of the Rights Agreement is hereby modified and
                  amended by adding the following sentence at the end thereof:

                  "Notwithstanding anything in this Agreement to the contrary,
                  neither Anadarko Petroleum Corporation, a Delaware corporation
                  ("Anadarko"), nor any of its Affiliates or Associates, shall
                  be deemed to be an Acquiring Person by virtue of the approval,
                  execution, or delivery of the Stock Option Agreement dated
                  April 2,


<PAGE>   2


                  2000, between the Company and Anadarko (the UPR Stock Option
                  Agreement"), or the acquisition of beneficial ownership of
                  Common Shares pursuant to such agreement."

         2.       Section 3(a) of the Rights Agreement is amended by adding the
                  following sentence at the end thereof:

                  "Notwithstanding anything in this Agreement to the contrary, a
                  Distribution Date shall not be deemed to have occurred as the
                  result of the execution of the UPR Stock Option Agreement or
                  the acquisition or transfer of Common Shares by the Company
                  pursuant to the UPR Stock Option Agreement."

         3.       Section 29 of the Rights Agreement is amended to add the
                  following sentence at the end thereof:

                  "Nothing in this Agreement shall be construed to give any
                  holder of Rights or any other Person any legal or equitable
                  rights, remedies, or claims under this Agreement by virtue of
                  the execution of the UPR Stock Option Agreement, or by virtue
                  of any of the transactions contemplated by such agreement.

         4.       This Amendment shall become effective as of the date of the
                  Merger Agreement. If the Merger Agreement is terminated
                  without the Effective Time (as defined in the Merger
                  Agreement) having occurred, this Amendment shall be null and
                  void and the Company shall promptly notify the Rights Agent in
                  writing of such an occurrence.

         5.       This Amendment shall be deemed to be a contract made under the
                  laws of the State of Utah and for all purposes shall be
                  governed by and construed in accordance with the laws of such
                  state applicable to contracts to be made and performed
                  entirely within such state.

         6.       This Amendment may be executed in any number of counterparts,
                  each of such counterparts shall for all purposes be deemed to
                  be an original, and all such counterparts shall together
                  constitute but one and the same instrument.

         7.       In all respects not inconsistent with the terms and provisions
                  of this Amendment, the Rights Agreement is hereby ratified,
                  adopted, approved, and confirmed. In executing and delivering
                  this Amendment, the Rights Agent shall be entitled to all of
                  the privileges and immunities afforded to the Rights Agent
                  under the terms and conditions of the Rights Agreement.

         8.       If any term, provision, covenant, or restriction of this
                  Agreement is held by a court of competent jurisdiction or
                  other authority to be invalid, void, or unenforceable, the
                  remainder of the terms, provisions, covenants, and
                  restrictions of this Amendment, and of the Rights Agreement,
                  shall remain in full force and effect and shall in no way be
                  affected, impaired, or invalidated.


<PAGE>   3



         IN WITNESS WHEREOF, the parties hereto having caused this Amendment to
be duly executed and attested, all as of the date and year first above written.

                             UNION PACIFIC RESOURCES GROUP INC.



                             By:
                                 -----------------------------------------------
                                 Name:    Kerry R. Brittain
                                 Title:   Vice President, General Counsel and
                                 Corporate Secretary



                             HARRIS TRUST AND SAVINGS BANK



                             By:
                                 -----------------------------------------------
                                      Name:
                                            ------------------------------------
                                      Title:
                                             -----------------------------------



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