PIONEER NATURAL RESOURCES CO
S-3, 1998-02-13
CRUDE PETROLEUM & NATURAL GAS
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<PAGE>   1
 
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 13, 1998
 
                                                     REGISTRATION NO. 333-
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                                    FORM S-3
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                             ---------------------
                       PIONEER NATURAL RESOURCES COMPANY
             (Exact name of Registrant as specified in its charter)
 
<TABLE>
<S>                                                 <C>
                     DELAWARE                                           75-2702753
          (State or other jurisdiction of                            (I.R.S. Employer
          incorporation or organization)                            Identification No.)

                                                                    SCOTT D. SHEFFIELD
                                                           PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                                             PIONEER NATURAL RESOURCES COMPANY
             1400 WILLIAMS SQUARE WEST                           1400 WILLIAMS SQUARE WEST
             5205 NORTH O'CONNOR BLVD.                           5205 NORTH O'CONNOR BLVD.
                IRVING, TEXAS 75039                                 IRVING, TEXAS 75039
                  (972) 444-9001                                      (972) 444-9001
(Address, including zip code, and telephone number,  (Name, address, including zip code, and telephone
  including area code, of Registrant's principal    number, including area code, of agent for service)
                 executive offices)
</TABLE>
 
                             ---------------------

                                With copies to:
 
<TABLE>
<C>                                                 <C>
                  MARK L. WITHROW                                    ROBERT L. KIMBALL
   EXECUTIVE VICE PRESIDENT AND GENERAL COUNSEL                   VINSON & ELKINS L.L.P.
         PIONEER NATURAL RESOURCES COMPANY                           2001 ROSS AVENUE
             1400 WILLIAMS SQUARE WEST                                  SUITE 3700
             5205 NORTH O'CONNOR BLVD.                              DALLAS, TEXAS 75201
                IRVING, TEXAS 75039                                   (214) 220-7700
                  (972) 444-9001
</TABLE>
 
                             ---------------------
 
    APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: From time
to time after this Registration Statement becomes effective.
 
    If the only securities being registered on this Form are being offered
pursuant to dividend or interest reinvestment plans, please check the following
box. [ ]
 
    If any of the securities being registered on this Form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, other than securities offered only in connection with dividend or interest
reinvestment plans, check the following box. [X]
 
    If the Registrant elects to deliver its latest annual report to security
holders, or a complete and legible facsimile thereof, pursuant to Item 11(a)(i)
of this Form, check the following box. [ ]
 
    If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list the Securities Act registration statement number of the earlier
effective registration statement for the same offering. [ ]
                                                           ------------------
 
    If this Form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [ ]
                          ------------------
 
    If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [ ]

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

                        CALCULATION OF REGISTRATION FEE
 
<TABLE>
<CAPTION>
===========================================================================================================================
                                                                    PROPOSED              PROPOSED
         TITLE OF EACH CLASS OF              AMOUNT TO BE       MAXIMUM OFFERING     MAXIMUM AGGREGATE        AMOUNT OF
       SECURITIES TO BE REGISTERED            REGISTERED        PRICE PER SHARE        OFFERING PRICE     REGISTRATION FEE
- ---------------------------------------------------------------------------------------------------------------------------
<S>                                       <C>                 <C>                  <C>                    <C>
Common Stock.............................    10,901,924(1)            (2)                   (2)                  (3)
===========================================================================================================================
</TABLE>
 
(1) Pursuant to Rule 429 under the Securities Act of 1993, the Prospectus
    constituting a part of this Registration Statement also relates to
    14,309,601 shares of Pioneer Common Stock previously registered under
    Registration Statement on Form S-3 No. 333-39381.
(2) Pursuant to Rule 457(f), the fee was computed on the basis of the market
    value of the 10,901,924 shares of Pioneer Common Stock to be issued by the
    Registrant in connection with the exchange of the Exchangeable Shares, and
    in accordance with Rule 457(c) on the basis of the average ($22.91) of the
    high and low price per share of the shares of Pioneer Common Stock reported
    on the New York Stock Exchange on February 10, 1998.
(3) A fee of $2,204.70 was paid in connection with the filing of Registration
    Statement No. 333-39381 on November 3, 1997. Pursuant to Rule 457(b), the
    initial fee of $220,470.70 was offset by the fee of $218,266 paid with the
    filing under the Securities Exchange Act of 1934 of preliminary copies of
    the Registrant's proxy materials relating to the Transaction.
 
     Pursuant to Rule 429 under the Securities Act of 1933, the Prospectus
included herein also relates to a total of 14,309,601 shares of Pioneer Common
Stock of the registrant previously registered pursuant to Rule 415 under
Registration Statement on Form S-3 No. 333-39381 and not issued. This
Registration Statement constitutes Post-Effective Amendment No. 1 to the
Registration Statement on Form S-3 No. 333-39381, and hereby deregisters
10,797,053 shares of Pioneer Common Stock previously registered on such
registration statement.
 
     THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT SHALL
FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS REGISTRATION
STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(a) OF
THE SECURITIES ACT OF 1933, OR UNTIL THE REGISTRATION STATEMENT SHALL BECOME
EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID SECTION 8(a),
MAY DETERMINE.
================================================================================
<PAGE>   2
 
Information contained herein is subject to completion or amendment. A
registration statement relating to these securities has been filed with the
Securities and Exchange Commission. These securities may not be sold nor may
offers to buy be accepted prior to the time the registration statement becomes
effective. This prospectus shall not constitute an offer to sell or the
solicitation of an offer to buy nor shall
there be any sale of these securities in any state in which such offer,
solicitation or sale would be unlawful prior to registration or qualification
under the securities laws of any such state.
 
                 SUBJECT TO COMPLETION DATED FEBRUARY 13, 1998
PROSPECTUS
                               10,901,924 SHARES
 
                       PIONEER NATURAL RESOURCES COMPANY
 
                                  COMMON STOCK
                          (PAR VALUE $0.01 PER SHARE)
 
     Each of the 10,901,924 shares of common stock, par value $0.01 per share
(the "Pioneer Common Stock"), of Pioneer Natural Resources Company, a Delaware
corporation ("Pioneer"), offered hereby is issuable upon the exchange or
redemption of an exchangeable share (an "Exchangeable Share") of Pioneer Natural
Resources (Canada) Ltd., an indirectly owned subsidiary of Pioneer ("Pioneer
Canada"). Pursuant to the Plan of Arrangement (as defined below), at the
Effective Time (as defined herein) Pioneer Canada, previously a British Columbia
corporation, was continued as an Alberta corporation. Certain of the
Exchangeable Shares were issued by Pioneer Canada upon the transfer of common
shares ("Chauvco Common Shares") of Chauvco Resources Ltd., an Alberta
corporation ("Chauvco"), pursuant to the terms of a Combination Agreement (the
"Combination Agreement") dated as of September 3, 1997, between Pioneer and
Chauvco and the terms of a plan of arrangement under Section 186 of the Business
Corporations Act (Alberta) (the "Plan of Arrangement") attached as an exhibit to
the Combination Agreement (the transactions contemplated by the Combination
Agreement and the Plan of Arrangement being referred to herein collectively as
the "Transaction"). The remaining Exchangeable Shares will be issued to two
Canadian former holders of Chauvco Common Shares in exchange for the capital
stock and debt of affiliate companies of such holders whose sole assets are
Exchangeable Shares acquired pursuant to the Plan of Arrangement (such
transaction being referred to herein as the "Exchange Transaction"). See "Plan
of Distribution -- Exchangeable Shares." Shares of Pioneer Common Stock are
being offered on a continuous basis pursuant to Rule 415 under the Securities
Act of 1933 (the "Securities Act") for such period as the Registration Statement
to which this Prospectus relates remains effective.
 
     Pioneer and Pioneer Canada are offering shares of Pioneer Common Stock to
holders of Exchangeable Shares pursuant to the terms of the Exchangeable Shares,
which obligate Pioneer Canada to redeem such shares or permit Pioneer, at its
election, to acquire such shares when, as and if the Exchangeable Shares are
presented by the holders thereof. Hereinafter the term "exchange" means either
the redemption by Pioneer Canada or the acquisition by Pioneer of Exchangeable
Shares, unless otherwise specified. Upon such exchange, holders of the
Exchangeable Shares will be entitled to receive for each Exchangeable Share one
share of Pioneer Common Stock, plus an additional amount equivalent to the full
amount of all declared and unpaid dividends on such Exchangeable Share (see
"Plan of Distribution"). All expenses of registration incurred in connection
with this offering are being paid by Pioneer. The Pioneer Common Stock currently
trades on the New York Stock Exchange (the "NYSE") under the symbol "PXD," and
The Toronto Stock Exchange (the "TSE") under the symbol "PXD". The Exchangeable
Shares currently trade on the TSE under the symbol "PCX." On February 10, 1998,
the closing price of the Pioneer Common Stock on the NYSE was $23 1/8 per share
and the closing price of the Pioneer Common Stock and the Exchangeable Shares on
the TSE was $21.60 and $22.65 per share, respectively.
                             ---------------------
 
      SEE "RISK FACTORS" BEGINNING ON PAGE 3 HEREOF FOR A DISCUSSION OF CERTAIN
FACTORS THAT SHOULD BE CONSIDERED IN CONNECTION WITH ANY INVESTMENT IN THE
PIONEER COMMON STOCK OFFERED HEREBY.
                             ---------------------
 
  THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
 EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION, NOR HAS THE SECURITIES
   AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO THE CONTRARY IS A
                               CRIMINAL OFFENSE.
 
               The date of this Prospectus is February 13, 1998.
<PAGE>   3
 
                             AVAILABLE INFORMATION
 
     Pioneer is subject to the informational requirements of the Securities
Exchange Act of 1934 (the "Exchange Act"). It files reports, proxy statements,
and other information with the Securities and Exchange Commission (the "SEC").
Those reports, proxy statements, and other information can be inspected and
copied at the public reference facilities maintained by the SEC at Room 1024,
450 Fifth Street, N.W., Washington, D.C. 20549, and at the regional offices of
the SEC at 7 World Trade Center, Suite 1300, New York, New York 10048, and 500
West Madison Street, Suite 1400, Chicago, Illinois 60611. Copies of these
materials can be obtained at prescribed rates from the Public Reference Section
of the SEC at 450 Fifth Street, N.W., Washington, D.C. 20549. These reports,
proxy statements and other information may also be obtained without charge from
the web site that the SEC maintains at http://www.sec.gov. These reports, proxy
statements, and other information also may be inspected at the offices of the
NYSE, 20 Broad Street, New York, New York 10005.
 
     Pioneer has filed with the SEC a Registration Statement on Form S-3 (the
"Registration Statement") under the Securities Act, with respect to the shares
of Pioneer Common Stock offered hereby. This Prospectus does not contain all the
information set forth in the Registration Statement, certain parts of which are
omitted in accordance with the rules and regulations of the SEC. For further
information with respect to Pioneer and the shares of Pioneer Common Stock
offered hereby, reference is made to the Registration Statement and to the
exhibits thereto. Statements contained herein concerning the provisions of
certain documents are not necessarily complete, and in each instance, reference
is made to the copy of the document filed as an exhibit to the Registration
Statement or otherwise filed with the SEC. Each such statement is qualified in
its entirety by that reference.
 
                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE
 
     The following documents have been filed by Pioneer, Parker & Parsley
Petroleum Company ("Parker & Parsley") and MESA Inc. ("Mesa") with the SEC, are
incorporated by reference into this Prospectus, and are deemed to be a part of
this Prospectus:
 
      1. Mesa's Annual Report on Forms 10-K and 10-K/A for the year ended
         December 31, 1996;
 
      2. Mesa's Quarterly Report on Form 10-Q for the period ended March 31,
         1997;
 
      3. Mesa's Current Reports on Form 8-K, dated February 7, 1997, and April
         6, 1997, and Mesa's Current Report on Form 8-K/A, dated February 7,
         1997;
 
      4. Mesa's Quarterly Report on Form 10-Q for the period ended June 30,
         1997;
 
      5. Parker & Parsley's Annual Report on Forms 10-K and 10-K/A for the year
         ended December 31, 1996;
 
      6. Parker & Parsley's Current Report on Form 8-K, dated February 3, 1997;
 
      7. Parker & Parsley's Quarterly Report on Form 10-Q for the period ended
         March 31, 1997;
 
      8. Parker & Parsley's Current Reports on Form 8-K, dated April 3, 1997,
         April 6, 1997, July 28, 1997, and July 29, 1997;
 
      9. Parker & Parsley's Quarterly Report on Form 10-Q for the period ended
         June 30, 1997;
 
     10. Pioneer's Registration Statement on Form S-4 (No. 333-26951) initially
         filed on June 26, 1997, as amended;
 
     11. Pioneer's Quarterly Report on Form 10-Q for the period ended June 30,
         1997;
 
     12. Pioneer's Current Report on Form 8-K, dated August 7, 1997;
 
     13. The description of Pioneer's Common Stock contained in Pioneer's
         Registration Statement on Forms 8-A and 8-A/A (File No. 001-13245),
         declared effective by the SEC on August 8, 1997;
 
                                        2
<PAGE>   4
 
     14. Pioneer's Current Report on Form 8-K, dated September 3, 1997;
 
     15. Pioneer's Quarterly Report on Form 10-Q for the period ended September
         30, 1997;
 
     16. The Definitive Joint Management Information Circular and Proxy
         Statement of Pioneer and Chauvco (File No. 001-13245) filed with the
         SEC on November 17, 1997, including any amendment or report for the
         purpose of updating any such material;
 
     17. Pioneer's Current Report on Form 8-K, dated December 5, 1997, as
         amended;
 
     18. Pioneer's Current Report on Form 8-K, dated December 18, 1997, as
         amended;
 
     19. Pioneer's and Pioneer Natural Resources USA, Inc.'s Current Report on
         Form 8-K, dated January 8, 1998; and
 
     20. Pioneer's and Pioneer Natural Resources USA, Inc.'s Current Report on
         Form 8-K, dated January 13, 1998; and
 
     21. Pioneer's Current Report on Form 8-K, dated February 10, 1998.
 
     All documents filed by Pioneer pursuant to Section 13(a), 14 or 15(d) of
the Exchange Act subsequent to the date of this Prospectus and prior to the
termination of the offering made hereby shall be deemed to be incorporated by
reference into this Prospectus and to be a part hereof from the date of the
filing of such documents. Any statement contained herein or in a document
incorporated or deemed to be incorporated by reference herein shall be deemed to
be modified or superseded for purposes of this Prospectus to the extent that a
statement contained herein or in any subsequently filed document that also is or
is deemed to be incorporated by reference herein modifies or supersedes such
statement. Any statement so modified or superseded shall not be deemed to
constitute a part of this Prospectus, except as so modified or superseded.
 
     Pioneer will provide without charge to each person to whom a copy of this
Prospectus has been delivered, on the written or oral request of any person, a
copy of any or all of the documents referred to above that have been or may be
incorporated by reference into this Prospectus, other than exhibits to the
documents (unless the exhibits are specifically incorporated by reference into
the documents). Written or telephone request for the copies should be directed
to Corporate Secretary, Pioneer Natural Resources Company, 1400 Williams Square
West, 5205 North O'Connor Boulevard, Irving, Texas 75039 (Telephone: (972)
444-9001).
 
                                  RISK FACTORS
 
     Investors should consider carefully the following factors, in addition to
the other information contained in this Prospectus, before exchanging their
Exchangeable Shares for the shares of Pioneer Common Stock offered hereby.
 
TAXABILITY OF THE EXCHANGE
 
     Based on the tax laws as of the date of this Prospectus, the exchange of
Exchangeable Shares for shares of Pioneer Common Stock is generally a taxable
event in Canada and the United States. A holder's tax consequences can vary
depending on a number of factors, including the residency of the holder, the
method of the exchange and the length of time that the Exchangeable Shares were
held prior to the exchange (see "Income Tax Considerations").
 
DIFFERENCES IN CANADA AND U.S. TRADING MARKETS
 
     The Pioneer Common Stock is listed on the NYSE and the TSE, and the
Exchangeable Shares are listed on the TSE. There is no current intention to list
the Exchangeable Shares or Pioneer Common Stock on any other stock exchange in
Canada or the United States. As a result of the foregoing, the price at which
the Exchangeable Shares trades is based upon the market for such shares on the
TSE, and the price at which the shares of Pioneer Common Stock trades is based
upon the market for such shares on the NYSE and TSE. Although Pioneer believes
that the market price of the Exchangeable Shares on the TSE and the market price
of the Pioneer Common Stock on the NYSE and TSE reflect essentially equivalent
values, there can be no
                                        3
<PAGE>   5
 
assurance that the market price of the Pioneer Common Stock will be identical,
or even similar, to the market price of the Exchangeable Shares.
 
FOREIGN PROPERTY
 
     So long as the Exchangeable Shares are listed on a prescribed stock
exchange in Canada (which currently includes the TSE) and Pioneer Canada
maintains a substantial presence in Canada, the Exchangeable Shares will not be
foreign property under the Income Tax Act (Canada) (the "Canadian Tax Act") for
trusts governed by registered pension plans, registered retirement savings
plans, registered retirement income funds and deferred profit sharing plans or
for certain other tax-exempt persons. Pioneer Common Stock will, however, be
foreign property for such plans or persons.
 
                                    PIONEER
 
     Pioneer is one of the largest public independent oil and gas companies in
the United States, engaged principally in the acquisition, development, and
production of, and exploration for, oil and gas reserves and related activities.
 
     Pioneer's executive offices and operating headquarters are located at 1400
Williams Square West, 5205 North O'Connor Blvd., Irving, Texas 75039, and its
telephone number at those offices is (972) 444-9001.
 
                                USE OF PROCEEDS
 
     Because shares of Pioneer Common Stock will be issued on the exchange of
the Exchangeable Shares, Pioneer will receive no cash proceeds on that issuance.
 
                          DESCRIPTION OF CAPITAL STOCK
 
     The authorized capital stock of Pioneer consists of 500,000,000 shares of
common stock, par value $.01 per share, and 100,000,000 shares of preferred
stock, par value $.01 per share, of which one share has been designated as
Special Preferred Voting Stock.
 
PIONEER CAPITAL STOCK
 
  Pioneer Common Stock
 
     All shares of Pioneer Common Stock issued upon the exchange of the
Exchangeable Shares will be fully paid and nonassessable. The holders of Pioneer
Common Stock are entitled to one vote for each share held on all matters
submitted to a vote of common stockholders. The Pioneer Common Stock does not
have cumulative voting rights. Shares of Pioneer Common Stock have no preemptive
rights, conversion rights, redemption rights or sinking fund provisions. Pioneer
Common Stock is not subject to redemption by Pioneer.
 
     Subject to the rights of the holders of any class of capital stock of
Pioneer having any preference or priority over the Pioneer Common Stock, the
holders of Pioneer Common Stock are entitled to dividends in such amounts as may
be declared by the Board of Directors of Pioneer (the "Pioneer Board") from time
to time out of funds legally available for such payments and, in the event of
liquidation, to share ratably in any assets of Pioneer remaining after payment
in full of all creditors and provision for any liquidation preferences on any
outstanding preferred stock ranking prior to the Pioneer Common Stock.
 
  Pioneer Preferred Stock
 
     The Pioneer Board, without further stockholder action, is authorized to
issue up to 100,000,000 shares of preferred stock in one or more series and to
fix and determine as to any series all the relative rights and preferences of
shares in the series, including voting rights, dividend rights, liquidation
preferences, terms of redemption, and conversion rights.
 
                                        4
<PAGE>   6
 
  Pioneer Special Preferred Voting Stock
 
     The Pioneer Board has designated one (1) of the 100,000,000 authorized
shares of preferred stock as Special Preferred Voting Stock (the "Voting
Share"). The Montreal Trust Company of Canada, or any successor thereto (the
"Trustee"), shall hold the Voting Share as trustee for and on behalf of, and for
the use and benefit of, the holders of Exchangeable Shares and in accordance
with the Voting and Exchange Trust Agreement. The Certificate of Designations
for the Voting Share includes the following principal terms:
 
     Dividends. No dividend shall be paid to the Trustee as the holder of the
Voting Share.
 
     Voting Rights. The Trustee, as the holder of record of the Voting Share,
shall be entitled to all of the voting rights attached to the Voting Share,
including the right to consent to or vote in person or by proxy the Voting
Share, on any matter, question or proposition whatsoever that may properly come
before the Pioneer stockholders at a meeting thereof or with respect to any
written consent sought by Pioneer from its stockholders. For each Exchangeable
Share owned of record on the relevant record date, the holder thereof shall be
entitled to instruct the Trustee to cast and exercise, in the manner instructed,
a number of votes (including for purposes of a quorum) equal to the number of
votes to which a holder of one share of Pioneer Common Stock is entitled with
respect to any matter, proposition or question on which the holders of Pioneer
Common Stock are entitled to vote. Except as otherwise described herein or
required by law, the holder of the Voting Share will vote together with the
Pioneer Common Stock as a single class and not as a separate class or series
apart therefrom, including any vote to approve or adopt: (i) any plan of merger,
consolidation or share exchange for which Delaware law requires a stockholder
vote; (ii) any disposition of assets for which Delaware law requires a
stockholder vote; and (iii) any dissolution of Pioneer for which Delaware law
requires a stockholder vote.
 
     The holders of Exchangeable Shares will have the right to submit
stockholder proposals to the Trustee and the Trustee will agree pursuant to the
Voting and Exchange Trust Agreement to submit any such proposals to Pioneer.
Such stockholder proposals may be considered at any meeting of Pioneer at which
the holders of Pioneer Common Stock are entitled to submit stockholder
proposals. Pioneer will agree pursuant to the Voting and Exchange Trust
Agreement to accept all stockholder proposals submitted by the Trustee provided
that not more than one proposal is submitted by the Trustee on behalf of any one
holder of Exchangeable Shares.
 
     So long as any Exchangeable Shares are outstanding, the number of shares
comprising the Special Preferred Voting Stock will not be increased or
decreased, and no other term of the Special Preferred Voting Stock may be
amended, except upon the approval of the holder of the Voting Share.
 
     Conversion. The Voting Share is not convertible into any other class or
series of the capital stock of Pioneer or into cash, property or other rights.
 
     Redemption. The Voting Share may not be redeemed, except at such time as no
Exchangeable Shares shall be outstanding, in which case, the Voting Share shall
be automatically redeemed. The redemption price due and payable upon such
automatic redemption will be equal to a $1.00 liquidation preference. The Voting
Share will be deemed retired and will be canceled upon any purchase or other
acquisition thereof by Pioneer. After such cancellation, the Voting Share may
not be reissued or otherwise disposed of by Pioneer.
 
     Liquidation. The Voting Share will rank prior to each share of Pioneer
Common Stock with respect to the distribution of assets upon a liquidation,
dissolution or winding-up of Pioneer. In the event of any such liquidation,
dissolution or winding-up, the holder of the Voting Share will be entitled to
receive, before any distribution to the holders of Pioneer Common Stock, but
only after the liquidation preference of any other shares of preferred stock of
Pioneer has been paid in full, a liquidation preference equal to $1.00.
 
     Certain Covenants of Pioneer. For so long as the Voting Share is
outstanding, Pioneer will: (i) fully comply with all terms of the Exchangeable
Shares and with all contractual obligations of Pioneer associated therewith, and
(ii) not amend, alter or repeal the terms and conditions of the Special
Preferred Voting Stock, except with the approval of the holder of the Voting
Share.
 
                                        5
<PAGE>   7
 
     For a more detailed description of Pioneer's Special Preferred Voting Stock
and the Voting Share, see the terms and conditions thereof set forth on Exhibit
3.3 to the Registration Statement of which this Prospectus is a part. See also
"-- Voting and Exchange Trust Agreement."
 
  Certain Provisions of the Certificate of Incorporation and Bylaws
 
     The Pioneer Board is divided into three classes. The directors of each
class are elected for three-year terms, with the terms of the three classes
staggered so that directors from a single class are elected at each annual
meeting of stockholders. Stockholders may remove a director only for cause. In
general, the Pioneer Board, not the stockholders, has the right to appoint
persons to fill vacancies on the Pioneer Board.
 
     The amended and restated certificate of incorporation of Pioneer (the
"Pioneer Restated Certificate") contains a "fair price" provision that requires
the affirmative vote of the holders of least 80% of Pioneer's voting stock and
the affirmative vote of at least 66 2/3% of Pioneer's voting stock not owned,
directly or indirectly, by a Pioneer Related Person (as defined below) to
approve any merger, consolidation, sale or lease of all or substantially all of
Pioneer's assets, or certain other transactions involving a Pioneer Related
Person. For purposes of this fair price provision, a "Pioneer Related Person" is
any person beneficially owning 10% or more of the voting power of the
outstanding capital stock of Pioneer who is a party to the transaction at issue.
The voting requirement is not applicable to certain transactions, including
those that are approved by Pioneer's Continuing Directors (as defined in the
Pioneer Restated Certificate) or that meet certain "fair price" criteria
contained in the Pioneer Restated Certificate.
 
     The Pioneer Restated Certificate further provides that stockholders may act
only at annual or special meetings of stockholders and not by written consent,
that special meetings of stockholders may be called only by the Pioneer Board,
and that only business proposed by the Pioneer Board may be considered at
special meetings of stockholders.
 
     The Pioneer Restated Certificate also provides that the only business
(including election of directors) that may be considered at an annual meeting of
stockholders, in addition to business proposed (or persons nominated to be
directors) by the directors of Pioneer, is business proposed (or persons
nominated to be directors) by stockholders who comply with the notice and
disclosure requirements set forth in the Pioneer Restated Certificate. In
general, the Pioneer Restated Certificate requires that a stockholder give
Pioneer notice of proposed business or nominations no later than 60 days before
the annual meeting of stockholders (meaning the date on which the meeting is
first scheduled and not postponements or adjournments thereof) or (if later) 10
days after the first public notice of the annual meeting is sent to common
stockholders. In general, the notice must also contain information about the
stockholder proposing the business or nomination, his interest in the business,
and (with respect to nominations for director) information about the nominee of
the nature ordinarily required to be disclosed in public proxy solicitations.
The stockholder also must submit a notarized letter from each of his nominees
stating the nominee's acceptance of the nomination and indicating the nominee's
intention to serve as director if elected.
 
     The Pioneer Restated Certificate also restricts the ability of stockholders
to interfere with the powers of the Board of Directors in certain specified
ways, including the constitution and composition of committees and the election
and removal of officers.
 
     The Pioneer Restated Certificate provides that approval by the holders of
at least 66 2/3% of the outstanding Pioneer voting stock is required to amend
the provisions of the Pioneer Restated Certificate discussed above and certain
other provisions, except that (a) approval by the holders of at least 80% of the
outstanding Pioneer voting stock together with approval by the holders of at
least 66 2/3% of the outstanding voting stock not owned, directly or indirectly,
by the Related Person, is required to amend the fair price provisions, and (b)
approval of the holders of at least 80% of the outstanding voting stock is
required to amend the provisions prohibiting stockholders from acting by written
consent.
 
                                        6
<PAGE>   8
 
  Delaware Anti-Takeover Statute
 
     Pioneer is a Delaware corporation and is subject to Section 203 of the
Delaware General Corporation Law. In general, Section 203 prevents an
"interested stockholder" (defined generally as a person owning 15% or more of
Pioneer's outstanding voting stock) from engaging in a "business combination"
(as defined in Section 203) with Pioneer for three years following the date that
person becomes an interested stockholder unless (a) before that person became an
interested stockholder, the Pioneer Board approved the transaction in which the
interested stockholder became an interested stockholder or approved the business
combination, (b) upon completion of the transaction that resulted in the
interested stockholder's becoming an interested stockholder, the interested
stockholder owns at least 85% of Pioneer voting stock outstanding at the time
the transaction commenced (excluding stock held by directors who are also
officers of Pioneer and by employee stock plans that do not provide employees
with the right to determine confidentially whether shares held subject to the
plan will be tendered in a tender or exchange offer), or (c) following the
transaction in which that person became an interested stockholder, the business
combination is approved by the Pioneer Board and authorized at a meeting of
stockholders by the affirmative vote of the holders of at least two-thirds of
the outstanding Pioneer voting stock not owned by the interested stockholder.
 
     Under Section 203, these restrictions also do not apply to certain business
combinations proposed by an interested stockholder following the announcement or
notification of one or certain extraordinary transactions involving Pioneer and
a person who was not an interested stockholder during the previous three years
or who became an interested stockholder with the approval of a majority of
Pioneer's directors, if that extraordinary transaction is approved or not
opposed by a majority of the directors before any person became an interested
stockholder in the previous three years or who were recommended for election or
elected to succeed such directors by a majority of such directors then in
office.
 
CHAUVCO SHARE CAPITAL
 
     The share capital of Chauvco consists of one class of common shares,
unlimited in number, and all of such shares which are issued and outstanding are
held by Pioneer Canada.
 
PIONEER CANADA SHARE CAPITAL
 
     The share capital of Pioneer Canada has the rights and preferences
summarized below. Such summary is qualified in its entirety by reference to the
Plan of Arrangement and the rights, privileges, restrictions and conditions
attaching to the Exchangeable Shares (the "Exchangeable Share Provisions") which
are Exhibits 2.3 and 3.4, respectively, to the Registration Statement of which
this Prospectus is a part.
 
     Pioneer Canada Common Voting Shares. The holders of common voting shares of
Pioneer Canada ("Pioneer Canada Common Voting Shares") are entitled to receive
notice of and to attend all meetings of the shareholders of Pioneer Canada and
are entitled to one vote for each share held of record on all matters submitted
to a vote of holders of Pioneer Canada Common Voting Shares. The holders of
Pioneer Canada Common Voting Shares are entitled to receive such dividends as
may be declared by the Pioneer Canada board of directors out of funds legally
available therefor. Holders of Pioneer Canada Common Voting Shares are entitled
upon any liquidation, dissolution or winding-up of Pioneer Canada, subject to
the prior rights of the holders of the Exchangeable Shares and to any other
shares ranking senior to the Pioneer Canada Common Voting Shares, to receive the
remaining property and assets of Pioneer Canada.
 
  Exchangeable Shares of Pioneer Canada
 
     Ranking. The Exchangeable Shares rank prior to the Pioneer Canada Common
Voting Shares and any other shares ranking junior to the Exchangeable Shares
with respect to the payment of dividends and the distribution of assets in the
event of the liquidation, dissolution or winding-up of Pioneer Canada.
 
     Dividends. Holders of Exchangeable Shares are entitled to receive dividends
equivalent to dividends paid from time to time by Pioneer on shares of Pioneer
Common Stock. The declaration date, record date and
 
                                        7
<PAGE>   9
 
payment date for dividends on the Exchangeable Shares are the same as that for
the corresponding dividends on the Pioneer Common Stock.
 
     Certain Restrictions. Without the approval of the holders of the
Exchangeable Shares, Pioneer Canada will not:
 
          (a) pay any dividend on the Pioneer Canada Common Voting Shares, or
     any other shares ranking junior to the Exchangeable Shares, other than
     stock dividends payable in such other shares ranking junior to the
     Exchangeable Shares;
 
          (b) redeem, purchase or make any capital distribution in respect of
     Pioneer Canada Common Voting Shares or any other shares ranking junior to
     the Exchangeable Shares;
 
          (c) redeem or purchase any other shares of Pioneer Canada ranking
     equally with the Exchangeable Shares with respect to the payment of
     dividends or on any liquidation distribution;
 
          (d) issue any Exchangeable Shares or any other shares of Pioneer
     Canada ranking equally with, or superior to, the Exchangeable Shares other
     than by stock dividends to the holders of the Exchangeable Shares or as
     contemplated in the Support Agreement to be entered into between Pioneer
     and Pioneer Canada (the "Support Agreement"); or
 
          (e) amend the articles or bylaws of Pioneer Canada.
 
     The restrictions in (a), (b) and (c) above will not apply at any time when
the dividends on the outstanding Exchangeable Shares corresponding to dividends
declared on the Pioneer Common Stock have been declared and paid in full.
 
     Liquidation. In the event of the liquidation, dissolution or winding-up of
Pioneer Canada a holder of Exchangeable Shares will be entitled to receive for
each Exchangeable Share one share of Pioneer Common Stock, together with a cash
amount equivalent to the full amount of all unpaid dividends on the Exchangeable
Shares. See "-- Voting and Exchange Trust Agreement."
 
     Retraction of Exchangeable Shares by Holders. A holder of Exchangeable
Shares is entitled at any time to require Pioneer Canada to retract (i.e.,
require Pioneer Canada to redeem) any or all of the Exchangeable Shares held by
such holder for one share of Pioneer Common Stock for each Exchangeable Share
plus an additional amount equivalent to the full amount of all unpaid dividends
thereon, which shall be delivered to the retracting holder on the retraction
date specified by the holder (which shall not be less than three nor more than
ten business days after the date on which Pioneer Canada receives the retraction
request from the holder).
 
     If, as a result of liquidity or solvency provisions of applicable law,
Pioneer Canada is not permitted to redeem all Exchangeable Shares tendered by a
retracting holder, Pioneer Canada will redeem only those Exchangeable Shares
tendered by the holder (rounded down to a whole number of shares) as would not
be contrary to such provisions of applicable law. The holder of any Exchangeable
Shares not redeemed by Pioneer Canada will be deemed to have required Pioneer to
purchase such unretracted shares in exchange for Pioneer Common Stock, plus an
additional amount equivalent to the full amount of all unpaid dividends thereon,
on the retraction date pursuant to the optional Exchange Rights (as defined
herein). See "-- Voting and Exchange Trust Agreement."
 
     Redemption of Exchangeable Shares. Subject to Pioneer's Redemption Call
Right (as defined below), on the Automatic Redemption Date (as defined below)
Pioneer Canada will redeem all but not less than all of the then outstanding
Exchangeable Shares for one share of Pioneer Common Stock for each Exchangeable
Share plus an additional amount equivalent to the full amount of all unpaid
dividends thereon. Pioneer Canada shall, at least 120 days prior to the
Automatic Redemption Date, provide the registered holders of the Exchangeable
Shares with written notice of the proposed redemption of the Exchangeable
Shares.
 
     "Automatic Redemption Date" means the fifth anniversary of the date of the
first issuance of Exchangeable Shares unless (a) such date shall be extended at
any time or from time to time to a specified
 
                                        8
<PAGE>   10
 
later date by the Board of Directors of Pioneer Canada, but not later than
December 31, 2005 or (b) such date shall be accelerated at any time to a
specified earlier date (but no earlier than the third anniversary of the first
issuance of Exchangeable Shares) by the Board of Directors of Pioneer Canada if
at such time there are issued and outstanding less than 5% of the number of
Exchangeable Shares initially issued and outstanding pursuant to the Plan of
Arrangement (other than Exchangeable Shares held by Pioneer and its
subsidiaries) and as such number of shares may be adjusted as deemed appropriate
by the Board of Directors of Pioneer Canada to give effect to any subdivision or
consolidation of or stock dividend on the Exchangeable Shares, any issuance or
distribution of rights to acquire Exchangeable Shares or securities exchangeable
for or convertible into Exchangeable Shares, any issue or distribution of other
securities or rights or evidences of indebtedness or assets, or any other
capital reorganization or other transaction affecting the Exchangeable Shares,
in which case the Automatic Redemption Date shall be such later or earlier date;
provided, however, that the accidental failure or omission to give any such
notice of extension or acceleration, as the case may be, to less than 10% of
such holders of Exchangeable Shares shall not affect the validity of such
extension or acceleration.
 
     Voting Rights. Except as required by applicable law, the holders of the
Exchangeable Shares shall not be entitled as such to receive notice of or attend
any meeting of the shareholders of Pioneer Canada or to vote at any such
meeting.
 
     Amendment and Approval. The rights, privileges, restrictions and conditions
attaching to the Exchangeable Shares may be changed only with the approval of
the holders thereof. Any such approval or any other approval or consent to be
given by the holders of the Exchangeable Shares will be sufficiently given if
given in accordance with applicable law and subject to a minimum requirement
that such approval or consent be evidenced by a resolution passed by not less
than two-thirds of the votes cast thereon (other than shares beneficially owned
by Pioneer or entities controlled by Pioneer) at a meeting of the holders of
Exchangeable Shares duly called and held at which holders of at least 50% of the
then outstanding Exchangeable Shares are present or represented by proxy. In the
event that no such quorum is present at such meeting within one-half hour after
the time appointed therefor, then the meeting will be adjourned to such place
and time not less than 10 days later as may be determined at the original
meeting and the holders of Exchangeable Shares present or represented by proxy
at the adjourned meeting may transact the business for which the meeting was
originally called. At the adjourned meeting, a resolution passed by the
affirmative vote of not less than two-thirds of the votes cast thereon will
constitute the approval or consent of the holders of the Exchangeable Shares.
 
     Actions of Pioneer Canada under Support Agreement. Under the Exchangeable
Share Provisions, Pioneer Canada agrees to take all such actions and do all such
things as are necessary or advisable to perform and comply with its obligations
under, and to ensure the performance and compliance by Pioneer with its
obligations under, the Support Agreement.
 
SUPPORT AGREEMENT
 
     The following is a summary description of the material provisions of the
Support Agreement and is qualified in its entirety by reference to the full text
of the Support Agreement, which is Exhibit 2.4 to the Registration Statement of
which this Prospectus is a part.
 
     Under the Support Agreement, Pioneer agrees that: (i) it will not declare
or pay dividends on the Pioneer Common Stock unless Pioneer Canada is able to
and simultaneously pays an equivalent dividend on the Exchangeable Shares; (ii)
it will cause Pioneer Canada to declare and pay an equivalent dividend on the
Exchangeable Shares simultaneously with Pioneer's declaration and payment of
dividends on the Pioneer Common Stock; (iii) it will take all actions and do all
things necessary to ensure that Pioneer Canada is able to provide to the holders
of the Exchangeable Shares the equivalent number of shares of Pioneer Common
Stock in the event of a liquidation, dissolution, or winding-up of Pioneer
Canada, a Retraction Request (as defined herein) by a holder of Exchangeable
Shares, or a redemption of Exchangeable Shares of Pioneer Canada; and (iv) it
will not vote or otherwise take any action or omit to take any action causing
the liquidation, dissolution or winding-up of Pioneer Canada.
 
     The Support Agreement also provides that, without the prior approval of
Pioneer Canada and the holders of the Exchangeable Shares, Pioneer will not
distribute additional shares of Pioneer Common Stock or rights
                                        9
<PAGE>   11
 
to subscribe therefor or other property or assets to all or substantially all
holders of shares of Pioneer Common Stock, nor change the Pioneer Common Stock
nor effect any tender offer, share exchange offer, issuer bid, take-over bid or
similar transaction affecting the Pioneer Common Stock, unless the same or an
equivalent distribution on or change to the Exchangeable Shares (or in the
rights of the holders thereof) is made simultaneously.
 
     Pioneer agrees that so long as there remain outstanding any Exchangeable
Shares not owned by Pioneer or any entity controlled by Pioneer, Pioneer will
remain the beneficial owner, directly or indirectly, of all outstanding shares
of Pioneer Canada other than the Exchangeable Shares. In addition, the Support
Agreement obligates Pioneer to nominate Messrs. James Baroffio and Guy J.
Turcotte to the board of directors of Pioneer in accordance with the same terms
as the Combination Agreement.
 
     With the exception of administrative changes for the purpose of adding
covenants for the protection of the holders of the Exchangeable Shares, making
certain necessary amendments or curing ambiguities or clerical errors (in each
case provided that the board of directors of each of Pioneer and Pioneer Canada
is of the opinion that such amendments are not prejudicial to the interests of
the holders of the Exchangeable Shares), the Support Agreement may not be
amended without the approval of the holders of the Exchangeable Shares.
 
     Under the Support Agreement, Pioneer agrees not to exercise any voting
rights attached to the Exchangeable Shares owned by it or any entity controlled
by it on any matter considered at meetings of holders of Exchangeable Shares
(including any approval sought from such holders in respect of matters arising
under the Support Agreement).
 
VOTING AND EXCHANGE TRUST AGREEMENT
 
     The following is a summary description of the material provisions of the
Voting and Exchange Trust Agreement and is qualified in its entirety by
reference to the full text of the Voting and Exchange Trust Agreement which is
Exhibit 2.5 to the Registration Statement of which this Prospectus is a part.
Under the terms of the Voting and Exchange Trust Agreement, Pioneer issued and
granted to the Trustee the (i) rights of the holders of Exchangeable Shares to
direct the voting of the Voting Share in accordance with the Voting and Exchange
Trust Agreement (the "Voting Rights") and (ii) the Automatic Exchange Rights (as
defined below) and the optional exchange right granted to the Trustee for the
use and benefit of the holders of the Exchangeable Shares pursuant to the Voting
and Exchange Trust Agreement to require Pioneer to purchase Exchangeable Shares
from the holders hereof in exchange for shares of Pioneer Common Stock upon the
occurrence of a Pioneer Canada Insolvency Event (as defined herein). "Automatic
Exchange Rights" means the rights granted to the Trustee for the benefit of the
holders of the Exchangeable Shares pursuant to the Voting and Exchange Trust
Agreement to automatically exchange the Exchangeable Shares for shares of
Pioneer Common Stock upon a Pioneer Liquidation Event (as defined herein).
 
     Voting Rights. Under the Voting and Exchange Trust Agreement, Pioneer
issued the Voting Share to the Trustee for the benefit of the holders (other
than Pioneer and its subsidiaries) of the Exchangeable Shares. The Voting Share
carries a number of votes, exercisable at any meeting at which Pioneer
Stockholders are entitled to vote, equal to the number of outstanding
Exchangeable Shares (other than shares held by Pioneer and its subsidiaries).
With respect to any written consent sought from the Pioneer Stockholders, each
vote attached to the Voting Share is exercisable in the same manner as set forth
above.
 
     Each holder of an Exchangeable Share on the record date for any meeting at
which Pioneer Stockholders are entitled to vote will be entitled to instruct the
Trustee to exercise one of the votes attached to the Voting Share for such
Exchangeable Share. The Trustee will exercise each vote attached to the Voting
Share only as directed by the relevant holder and, in the absence of
instructions from a holder as to voting, will not exercise such votes. A holder
may, upon instructing the Trustee, obtain a proxy from the Trustee entitling the
holder to vote directly at the relevant meeting the votes attached to the Voting
Share to which the holder is entitled.
 
     The Trustee will send to the holders of the Exchangeable Shares the notice
of each meeting at which the Pioneer Stockholders are entitled to vote, together
with the related meeting materials and a statement as to
 
                                       10
<PAGE>   12
 
the manner in which the holder may instruct the Trustee to exercise the votes
attaching to the Voting Share, at the same time as Pioneer sends such notice and
materials to the Pioneer Stockholders. The Trustee will also send to the holders
copies of all information statements, interim and annual financial statements,
reports and other materials sent by Pioneer to the Pioneer Stockholders at the
same time as such materials are sent to the Pioneer Stockholders. To the extent
such materials are provided to the Trustee by Pioneer, the Trustee will also
send to the holders all materials sent by third parties to Pioneer Stockholders,
including dissident proxy circulars and tender and exchange offer circulars, as
soon as possible after such materials are first sent to Pioneer Stockholders.
 
     All rights of a holder of Exchangeable Shares to exercise votes attached to
the Voting Share will cease upon the exchange of all such holder's Exchangeable
Shares for shares of Pioneer Common Stock.
 
     Exchange Rights. Under the Voting and Exchange Trust Agreement, Pioneer
granted the Exchange Rights (as defined below) to the Trustee for the benefit of
the holders of the Exchangeable Shares. "Exchange Rights" means the Automatic
Exchange Rights and the optional exchange right granted to the Trustee for the
use and benefit of the holders of the Exchangeable Shares pursuant to the Voting
and Exchange Trust Agreement to require Pioneer to purchase Exchangeable Shares
from the holders thereof in exchange for shares of Pioneer Common Stock upon the
occurrence of a Pioneer Canada Insolvency Event.
 
     Optional Exchange Right. Upon the occurrence and during the continuance of
a Pioneer Canada Insolvency Event, a holder of Exchangeable Shares will be
entitled to instruct the Trustee to exercise the optional Exchange Right with
respect to any or all of the Exchangeable Shares held by such holder, thereby
requiring Pioneer to purchase such Exchangeable Shares from the holder.
Immediately upon the occurrence of a Pioneer Canada Insolvency Event or any
event which may with the passage of time or the giving of notice become a
Pioneer Canada Insolvency Event, Pioneer Canada and Pioneer will give written
notice thereof to the Trustee. As soon as practicable thereafter, the Trustee
will notify each holder of Exchangeable Shares of such event or potential event
and will advise the holder of its rights with respect to the optional Exchange
Right. "Pioneer Canada Insolvency Event" means any insolvency or bankruptcy
proceeding instituted by or against Pioneer Canada, including any such
proceeding under the Companies' Creditors Arrangement Act (Canada) and the
Bankruptcy and Insolvency Act (Canada) and the admission in writing by Pioneer
Canada of its inability to pay its debts generally as they become due and the
inability of Pioneer Canada, as a result of solvency requirements of applicable
law, to redeem any Exchangeable Shares tendered for retraction.
 
     The consideration for each Exchangeable Share to be acquired under the
optional Exchange Right will be one share of Pioneer Common Stock plus an
additional amount equivalent to the full amount of all dividends declared and
unpaid on the Exchangeable Share.
 
     If, as a result of liquidity or solvency provisions of applicable law,
Pioneer Canada is unable to redeem all of the Exchangeable Shares tendered for
retraction by a holder in accordance with the Exchangeable Share Provisions, the
holder will be deemed to have exercised the optional Exchange Right with respect
to the unredeemed Exchangeable Shares and Pioneer will be required to purchase
such shares from the holder in the manner set forth above.
 
     Automatic Exchange Right. In the event of a Pioneer Liquidation Event,
Pioneer will be required to acquire each outstanding Exchangeable Share by
exchanging one share of Pioneer Common Stock for each such Exchangeable Share,
plus an additional amount equivalent to the full amount of all declared and
unpaid dividends on the Exchangeable Shares. "Pioneer Liquidation Event" means
(i) any determination by the Pioneer Board to institute voluntary liquidation,
dissolution, or winding-up proceedings with respect to Pioneer or to effect any
other distribution of assets of Pioneer among its stockholders for the purpose
of winding up its affairs; or (ii) immediately upon the earlier of (A) receipt
by Pioneer of notice of, and (B) Pioneer becoming aware of any threatened or
instituted claim, suit, petition or other proceedings with respect to the
involuntary liquidation, dissolution or winding-up of Pioneer or to effect any
other distribution of assets of Pioneer among its stockholders for the purpose
of winding-up its affairs.
 
                                       11
<PAGE>   13
 
DELIVERY OF PIONEER COMMON STOCK
 
     Pioneer will ensure that all shares of Pioneer Common Stock to be delivered
by it under the Support Agreement or on the exercise of the Exchange Rights
under the Voting and Exchange Trust Agreement are duly registered, qualified or
approved under applicable Canadian and United States securities laws, if
required so that such shares may be freely traded by the holder thereof (other
than any restriction on transfer by reason of a holder being a "control person"
of Pioneer for purposes of Canadian law or an "affiliate" of Pioneer for
purposes of United States law). In addition, Pioneer will take all actions
necessary to cause all such shares of Pioneer Common Stock to be listed or
quoted for trading on all stock exchanges or quotation systems on which
outstanding shares of Pioneer Common Stock are then listed or quoted for
trading.
 
CALL RIGHTS
 
     The following description of (i) the right of Pioneer, in the event of a
proposed liquidation, dissolution or winding-up of Pioneer Canada, to purchase
all of the outstanding Exchangeable Shares from the holders thereof on the
effective date of any such liquidation, dissolution or winding-up in exchange
for shares of Pioneer Common Stock pursuant to the Plan of Arrangement (the
"Liquidation Call Right"), (ii) the right of Pioneer to purchase all of the
outstanding Exchangeable Shares from the holders thereof on the Automatic
Redemption Date in exchange for shares of Pioneer Common Stock pursuant to the
Plan of Arrangement (the "Redemption Call Right") and (iii) the overriding right
of Pioneer, in the event of a proposed retraction of Exchangeable Shares by a
holder thereof, to purchase from such holder on the Retraction Date (as defined
herein) the Exchangeable Shares tendered for retraction in exchange for shares
of Pioneer Common Stock pursuant to the Exchangeable Share Provisions (the
"Retraction Call Right", and, together with the Liquidation Call Right and the
Redemption Call Right, the "Call Rights"), is qualified in its entirety by
reference to the full text of the Plan of Arrangement and the Exchangeable Share
Provisions, which are attached as Exhibits 2.3. and 3.4, respectively, to the
Registration Statement of which this Prospectus is a part.
 
     In the circumstances described below, Pioneer will have certain overriding
rights to acquire Exchangeable Shares from holders thereof for one share of
Pioneer Common Stock for each Exchangeable Share acquired, plus an amount
equivalent to the full amount of all declared and unpaid dividends on the
Exchangeable Shares. Different Canadian federal income tax consequences to a
holder of Exchangeable Shares may arise depending upon whether the Call Rights
are exercised by Pioneer or whether the relevant Exchangeable Shares are
redeemed by Pioneer Canada pursuant to the Exchangeable Share Provisions in the
absence of the exercise by Pioneer of the Call Rights. See "Income Tax
Considerations -- Canadian Federal Income Tax Considerations."
 
     Retraction Call Right. Pursuant to the Exchangeable Share Provisions, a
holder requesting Pioneer Canada to redeem the Exchangeable Shares will be
deemed to offer such shares to Pioneer, and Pioneer will have an overriding
Retraction Call Right to acquire all but not less than all of the Exchangeable
Shares that the holder has requested Pioneer Canada to redeem in exchange for
one share of Pioneer Common Stock for each Exchangeable Share, plus an
additional amount equivalent to the full amount of all declared and unpaid
dividends thereon.
 
     At the time of a Retraction Request by a holder of Exchangeable Shares,
Pioneer Canada will immediately notify Pioneer. Pioneer must then advise Pioneer
Canada within two business days as to whether Pioneer will exercise the
Retraction Call Right. If Pioneer does not advise Pioneer Canada within such two
business day period, Pioneer Canada will notify the holder as soon as possible
thereafter that Pioneer will not exercise the Retraction Call Right. A holder
may revoke his or her Retraction Request, at any time prior to the close of
business on the business day preceding the Retraction Date in which case the
holder's Exchangeable Shares will neither be purchased by Pioneer nor redeemed
by Pioneer Canada. If the holder does not revoke his or her Retraction Request,
on the Retraction Date the Exchangeable Shares that the holder has requested
Pioneer Canada to redeem will be acquired by Pioneer (assuming Pioneer exercises
its Retraction Call Right) or redeemed by Pioneer Canada, as the case may be, in
each case for one share of Pioneer Common Stock for each Exchangeable Share plus
an additional amount equivalent to the full amount of all declared and unpaid
dividends on the Exchangeable Shares.
 
                                       12
<PAGE>   14
 
     Liquidation Call Right. Pursuant to the Plan of Arrangement, Pioneer was
granted an overriding Liquidation Call Right, in the event of and
notwithstanding a proposed Pioneer Canada Insolvency Event, to acquire all but
not less than all of the Exchangeable Shares then outstanding in exchange for
Pioneer Common Stock and, upon the exercise by Pioneer of the Liquidation Call
Right, the holders thereof will be obligated to transfer such shares to Pioneer.
The acquisition by Pioneer of all of the outstanding Exchangeable Shares upon
the exercise of the Liquidation Call Right will occur on the effective date of
the voluntary or involuntary liquidation, dissolution or winding-up of Pioneer
Canada.
 
     Redemption Call Right. Pursuant to the Plan of Arrangement, Pioneer was
granted an overriding Redemption Call Right, notwithstanding the proposed
automatic redemption of the Exchangeable Shares by Pioneer Canada pursuant to
the Exchangeable Share Provisions, to acquire on the Automatic Redemption Date
all but not less than all of the Exchangeable Shares then outstanding in
exchange for Pioneer Common Stock plus an additional amount equivalent to the
full amount of all declared and unpaid dividends on the Exchangeable Shares and,
upon the exercise by Pioneer of the Redemption Call Right, the holders thereof
will be obligated to transfer such shares to Pioneer.
 
     Effect of Call Right Exercise. If Pioneer exercises one or more of its Call
Rights, it will directly issue shares of Pioneer Common Stock to holders of
Exchangeable Shares and will become the holder of such Exchangeable Shares.
Pioneer will not be entitled to exercise any voting rights attached to the
Exchangeable Shares it so acquires. If Pioneer declines to exercise its Call
Rights when applicable, it will be required, pursuant to the Support Agreement,
to issue shares of Pioneer Common Stock to Pioneer Canada which will, in turn,
transfer such stock to the holders of Exchangeable Shares in consideration for
the return and cancellation of such Exchangeable Shares. The tax consequences
resulting from Pioneer's exercise of one or more of the Call Rights are
discussed in "Income Tax Considerations -- Canadian Federal Income Tax
Considerations," which includes a discussion of deemed dividends and Part VI.1
tax.
 
                              PLAN OF DISTRIBUTION
 
EXCHANGEABLE SHARES
 
     Pursuant to the terms of the Combination Agreement, Pioneer Canada acquired
all the outstanding Chauvco Common Shares in an arrangement subject to the
approval by the Court of Queen's Bench of Alberta pursuant to Part 15 of the
Business Corporations Act (Alberta). On December 18, 1997 (the "Effective
Date"), each existing holder of Chauvco Common Shares automatically transferred
each Chauvco Common Share such holder held to Pioneer Canada in consideration
for (i) a number of shares of Pioneer Common Stock or Exchangeable Shares, or a
combination of both, determined in accordance with an agreed-upon exchange ratio
(the "Exchange Ratio") and, in certain cases, based upon such holder's election,
and (ii) one common share ("CRI Share") of Chauvco Resources International Ltd.
("CRI"), a wholly-owned subsidiary of Chauvco which has its principal
properties, operations and oil reserves located in Gabon, central west Africa.
Only holders resident in Canada could opt to elect to receive Exchangeable
Shares, and such holders could opt to elect to have their Chauvco Common Shares
transferred for a combination of shares of Pioneer Common Stock and Exchangeable
Shares. In addition, each existing holder of options to purchase Chauvco Common
Shares automatically transferred to Pioneer Canada each Chauvco option such
holder held in consideration for (i) one CRI Share and (ii) a number of shares
of Pioneer Common Stock determined in accordance with the Exchange Ratio and in
accordance with the holder's election of whether or not to pay the exercise
price of such Chauvco option in cash. As a result of the Arrangement, Chauvco
became a wholly-owned subsidiary of Pioneer Canada, and CRI was transferred to
Chauvco's shareholders and optionholders. Chauvco's name was subsequently
changed to Pioneer Natural Resources Canada Inc.
 
     In addition to distribution of the Exchangeable Shares pursuant to the
terms of the Combination Agreement described above, Pioneer Canada will issue
Exchangeable Shares (the "New Exchangeable Shares" and, together with the
Exchangeable Shares, the "Exchangeable Shares") to three Canadian former holders
of Chauvco Common Shares in exchange for the capital stock and debt of affiliate
companies of such holders whose sole assets are Exchangeable Shares acquired
pursuant to the Plan of Arrangement (the "Old
 
                                       13
<PAGE>   15
 
Exchangeable Shares"). The New Exchangeable Shares to be issued will be equal in
number to the Old Exchangeable Shares owned by such affiliate companies, such
that the total number of Exchangeable Shares outstanding after the occurrence of
the Exchange Transaction will be equal to the number of Exchangeable Shares
outstanding on the Effective Date, except for any retractions of Exchangeable
Shares that have occurred after the Effective Date.
 
     Prior to the Effective Date, one of Chauvco's major shareholders, Trimac
Corporation ("Trimac"), requested that Pioneer make certain changes to the terms
of the Transaction that would provide Trimac with certain tax benefits under
Canadian law. Pioneer did not agree to make any of the requested changes at such
time. However, Pioneer informed Trimac that it would consider entering into a
transaction proposed to Pioneer within 30 days after the Effective Date by
Trimac or any other original holder of Exchangeable Shares designed to enable
the holder to achieve tax benefits under Canadian law if, in the opinion of
Pioneer, such transaction would have no adverse effect on Pioneer or its
subsidiaries and if such holder of Exchangeable Shares was willing to provide
Pioneer with consideration that it deemed appropriate (including, without
limitation, cash payments, expense reimbursements, indemnification and
contractual transfer restrictions on the Exchangeable Shares).
 
     During the 30-day period after the Effective Date, Pioneer received two
such proposals from Trimac and Guy Turcotte, an individual. Both of Trimac and
Mr. Turcotte were formerly affiliates of Chauvco and, in addition, Mr. Turcotte
will be a nominee for Pioneer's board of directors at the next annual meeting of
Pioneer's stockholders. Affiliate companies of Trimac and Mr. Turcotte own
3,113,624 and 581,064 Exchangeable Shares, respectively. The affiliate companies
of Trimac and Mr. Turcotte will be dissolved immediately following the Exchange
Transaction. As a part of such dissolutions, the Old Exchangeable Shares will be
conveyed to Pioneer Canada and cancelled, such that the Old Exchangeable Shares
will no longer be issued and outstanding. The Share Purchase Agreements entered
into by Pioneer Canada with each of Trimac and Mr. Turcotte pursuant to which
Pioneer Canada will issue the New Exchangeable Shares are included as Exhibits
10.58 and 10.59 to the Registration Statement of which this Prospectus is a
part.
 
     Pursuant to the Share Purchase Agreements, both of Trimac and Mr. Turcotte
have agreed not to voluntarily transfer the New Exchangeable Shares except
pursuant to the provisions of the Exchangeable Shares and related agreements.
 
     Pioneer Common Stock may be issued to holders of Exchangeable Shares as
follows: (i) holders of Exchangeable Shares may require at any time that such
shares be exchanged for an equivalent number of shares of Pioneer Common Stock
plus an additional amount equivalent to all declared and unpaid dividends on
such Exchangeable Shares (see "-- Procedures for Issuance of Pioneer Common
Stock -- Exchange and Call Right"); (ii) subject to applicable law and the
Redemption Call Rights of Pioneer described below, Pioneer Canada must redeem
such Exchangeable Shares on the Automatic Redemption Date by exchanging therefor
an equal number of shares of Pioneer Common Stock plus an additional amount
equivalent to the full amount of all declared and unpaid dividends on such
Exchangeable Shares (see "-- Procedures for Issuance of Pioneer Common
Stock -- Exchange and Call Right"); (iii) upon the occurrence of a Pioneer
Canada Insolvency Event, holders of Exchangeable Shares may elect to, or, in the
case of Pioneer's exercise of the Liquidation Call Right, will be obligated to,
exchange such Exchangeable Shares for shares of Pioneer Common Stock (see
"-- Procedures for Issuance of Pioneer Common Stock -- Liquidation Rights of
Holders of Exchangeable Shares"); and (iv) upon the occurrence of a Pioneer
Liquidation Event, Pioneer will be required to acquire each outstanding
Exchangeable Share by exchanging one share of Pioneer Common Stock for each such
Exchangeable Share, plus an additional amount equivalent to the full amount of
all declared and unpaid dividends on the Exchangeable Shares (see "-- Procedures
for Issuance of Pioneer Common Stock -- Liquidation Rights of Holders of
Exchangeable Shares").
 
PROCEDURES FOR ISSUANCE OF PIONEER COMMON STOCK
 
     Exchange and Call Right. Holders of the Exchangeable Shares will be
entitled at any time following the Effective Time to retract (i.e., require
Pioneer Canada to redeem) any or all such Exchangeable Shares owned by them and
to receive an equivalent number of shares of Pioneer Common Stock plus an
additional amount equivalent to all declared and unpaid dividends on such
Exchangeable Shares. Holders of the
                                       14
<PAGE>   16
 
Exchangeable Shares may effect such retraction by presenting a certificate or
certificates to Pioneer Canada or its transfer agent representing the number of
Exchangeable Shares the holder desires to retract together with a duly executed
statement in the form of Exhibit A to the Exchangeable Share Provisions or in
such other form as may be acceptable to Pioneer Canada (the "Retraction
Request") specifying the number of Exchangeable Shares the holder wishes to
retract and the date upon which the holder desires to receive the Pioneer Common
Stock, which must be between three and 10 business days after the request is
received by Pioneer Canada (the "Retraction Date"), and such other documents as
may be required to effect the retraction of the Exchangeable Shares.
 
     Upon receipt of the Exchangeable Shares, the Retraction Request and other
required documentation from the holder thereof, Pioneer Canada must immediately
notify Pioneer of such Retraction Request. Pioneer will thereafter have two
business days in which to exercise the Retraction Call Right to purchase all of
the Exchangeable Shares submitted by the holder thereof by the delivery of an
equivalent number of shares of Pioneer Common Stock plus an additional amount
equivalent to the full amount of all declared and unpaid dividends on the
Exchangeable Shares to the transfer agent for delivery to such holder on the
Retraction Date. In the event Pioneer determines not to exercise its Retraction
Call Right and provided that the Retraction Request is not revoked in accordance
with the Exchangeable Share Provisions, Pioneer Canada is obligated to deliver
to the holder the number of shares of Pioneer Common Stock equal to the number
of Exchangeable Shares submitted by the holder for retraction and payment of an
additional amount equivalent to the full amount of all declared and unpaid
dividends on such Exchangeable Shares by the Retraction Date.
 
     Subject to applicable law and the Redemption Call Rights of Pioneer
described below, on the Automatic Redemption Date, Pioneer Canada must redeem
all but not less than all of the then outstanding Exchangeable Shares in
exchange for an equal number of shares of Pioneer Common Stock, plus an
additional amount equivalent to the full amount of all declared and unpaid
dividends on such Exchangeable Shares. Notwithstanding any proposed redemption
of the Exchangeable Shares of Pioneer Canada, Pioneer will have the overriding
right to purchase on the Automatic Redemption Date all but not less than all of
the then outstanding Exchangeable Shares in exchange for one share of Pioneer
Common Stock for each such Exchangeable Share, plus an additional amount
equivalent to the full amount of all declared and unpaid dividends on such
Exchangeable Share. Pioneer Canada shall, at least 120 days before the Automatic
Redemption Date, provide the registered holders of Exchangeable Shares with
written notice of the proposed redemption or purchase of the Exchangeable Shares
by Pioneer Canada or Pioneer, as the case may be. For a more detailed
description of the Exchange Rights and the Call Rights in connection with the
Exchangeable Shares, see "Description of Capital Stock -- Pioneer Canada Share
Capital -- Exchangeable Shares of Pioneer Canada," "-- Voting and Exchange Trust
Agreement -- Exchange Rights" and "-- Call Rights."
 
     Effect of Call Right Exercise. If Pioneer exercises one or more of its Call
Rights, it will directly issue shares of Pioneer Common Stock to holders of
Exchangeable Shares and will become the holder of such Exchangeable Shares.
Pioneer will not be entitled to exercise any voting rights attached to the
Exchangeable Shares it so acquires. If Pioneer declines to exercise its Call
Rights when applicable, it will be required, pursuant to the Support Agreement,
to issue Pioneer Common Stock to Pioneer Canada which will, in turn, transfer
such stock to the holders of Exchangeable Shares in consideration for the return
and cancellation of such Exchangeable Shares. The tax consequences resulting
from Pioneer's exercise of one or more of the Call Rights are discussed in
"Income Tax Considerations -- Canadian Federal Income Tax Considerations," which
includes a discussion of deemed dividends and Part VI.1 tax.
 
     Upon the occurrence of a Pioneer Canada Insolvency Event, holders of the
Exchangeable Shares will have preferential rights to receive from Pioneer one
share of Pioneer Common Stock for each Exchangeable Share they hold, plus an
additional amount equivalent to the full amount of any declared and unpaid
dividends on each such Exchangeable Share. In the event of a proposed Pioneer
Canada Insolvency Event, Pioneer will have the right to purchase all of the
outstanding Exchangeable Shares from the holders thereof at the effective time
of any such liquidation, dissolution, or winding up in exchange for one share of
Pioneer Common Stock for each such Exchangeable Share, plus an additional amount
equivalent to the full amount of all declared and unpaid dividends on such
Exchangeable Share.
 
                                       15
<PAGE>   17
 
     Upon the occurrence of a Pioneer Liquidation Event, in order for the
holders of the Exchangeable Shares to participate on a pro rata basis with the
holders of Pioneer Common Stock, each holder of Exchangeable Shares will
automatically receive in exchange therefor an equivalent number of shares of
Pioneer Common Stock, plus an additional amount equivalent to the full amount of
any declared and unpaid dividends on such Exchangeable Shares. For a more
detailed description of the Exchange Rights and the Call Rights in connection
with the Exchangeable Shares, see "Description of Capital Stock -- Voting and
Exchange Trust Agreement."
 
                           INCOME TAX CONSIDERATIONS
 
CANADIAN FEDERAL INCOME TAX CONSIDERATIONS
 
     In the opinion of MacKimmie Matthews, Canadian tax counsel for Pioneer
Canada, the following is a summary of the principal Canadian federal income tax
considerations generally applicable to the holders of Exchangeable Shares (the
"Pioneer Canada Shareholders") who, for purposes of the Canadian Tax Act, will
hold their Exchangeable Shares and shares of Pioneer Common Stock as capital
property and deal at arm's length with Pioneer and Pioneer Canada. This summary
does not apply to a holder with respect to whom Pioneer is a foreign affiliate
within the meaning of the Canadian Tax Act.
 
     All Pioneer Canada Shareholders should consult their own tax advisors as to
whether, as a matter of fact, they hold their Exchangeable Shares and shares of
Pioneer Common Stock as capital property for the purposes of the Canadian Tax
Act. In addition, the mark-to-market rules contained in the Canadian Tax Act
relating to financial institutions (including certain financial institutions,
registered securities dealers and corporations controlled by one or more of the
foregoing) will deem such financial institutions not to hold their Exchangeable
Shares and shares of Pioneer Common Stock as capital property for purposes of
the Canadian Tax Act. Pioneer Canada Shareholders that are financial
institutions should consult their own tax advisors to determine the tax
consequences to them of the application of the mark-to-market rules.
 
     This summary is based on the current provisions of the Canadian Tax Act,
the regulations thereunder, the current provisions of the Canada-United States
Income Tax Convention, 1980, as amended (the "Tax Treaty"), and Canadian tax
counsel's understanding of the current administrative practices of Revenue
Canada, Customs, Excise and Taxation ("Revenue Canada"). This summary takes into
account the amendments to the Canadian Tax Act and regulations publicly
announced by the Minister of Finance prior to the date hereof (the "Proposed
Amendments") and assumes that all Proposed Amendments will be enacted in their
present form. However, no assurances can be given that the Proposed Amendments
will be enacted in the form proposed, or at all.
 
     Except for the foregoing, this summary does not take into account or
anticipate any changes in law, whether by legislative, administrative or
judicial decision or action, nor does it take into account provincial,
territorial or foreign income tax legislation or considerations, which may
differ from the Canadian federal income tax considerations described herein.
 
     WHILE THIS SUMMARY IS INTENDED TO ADDRESS ALL PRINCIPAL CANADIAN FEDERAL
INCOME TAX CONSIDERATIONS, IT IS OF A GENERAL NATURE ONLY AND IS NOT INTENDED TO
BE, NOR SHOULD IT BE CONSTRUED TO BE, LEGAL OR TAX ADVICE TO ANY PARTICULAR
PIONEER CANADA SHAREHOLDER. THEREFORE, EACH PIONEER CANADA SHAREHOLDER IS URGED
TO CONSULT WITH SUCH SHAREHOLDER'S OWN TAX ADVISORS WITH RESPECT TO SUCH
SHAREHOLDER'S PARTICULAR CIRCUMSTANCES. NO ADVANCE INCOME TAX RULING HAS BEEN
OBTAINED FROM REVENUE CANADA TO CONFIRM THE TAX CONSEQUENCES OF ANY OF THE
TRANSACTIONS DESCRIBED HEREIN.
 
     For purposes of the Canadian Tax Act, all amounts relating to the
acquisition, holding or disposition of shares of Pioneer Common Stock, including
dividends, adjusted cost base and proceeds of disposition must be
 
                                       16
<PAGE>   18
 
converted into Canadian dollars based on the prevailing United States dollar
exchange rate at the time such amounts arise.
 
  Pioneer Canada Shareholders Resident in Canada
 
     The following portion of the summary is applicable to Pioneer Canada
Shareholders who, for purposes of the Canadian Tax Act, are resident or deemed
to be resident in Canada.
 
     Dividends Paid on Exchangeable Shares. A shareholder who is an individual
will include dividends received or deemed to be received on the Exchangeable
Shares in computing the shareholder's income, and will be subject to the
gross-up and dividend tax credit rules normally applicable to taxable dividends
received from taxable Canadian corporations.
 
     Subject to the special rules described below, in the case of a shareholder
that is a corporation, dividends received or deemed to be received on the
Exchangeable Shares will normally be deductible in computing its taxable income.
A shareholder that is a "private corporation" (as defined in the Canadian Tax
Act), or any other corporation resident in Canada and controlled or deemed to be
controlled by or for the benefit of an individual or a related group of
individuals, may be liable under Part IV of the Canadian Tax Act to pay a
refundable tax of 33 1/3% on dividends received or deemed to be received on the
Exchangeable Shares to the extent that such dividends are deductible in
computing the shareholder's taxable income.
 
     Special rules will apply to certain corporations that receive dividends on
the Exchangeable Shares:
 
          (a) In the case of a shareholder that is a "specified financial
     institution" under the Canadian Tax Act, a dividend received on its
     Exchangeable Shares will be deductible in computing its taxable income only
     if either:
 
             (i) the specified financial institution did not acquire the
        Exchangeable Shares in the ordinary course of the business carried on by
        such institution; or
 
             (ii) at the time of the receipt of the dividend by the specified
        financial institution, the Exchangeable Shares are listed on a
        prescribed stock exchange in Canada (which currently includes the TSE)
        and the specified financial institution, either alone or together with
        persons with whom it does not deal at arm's length, does not receive (or
        is not deemed to receive) dividends in respect of more than 10% of the
        issued and outstanding Exchangeable Shares.
 
          (b) If Pioneer Canada or any person with whom Pioneer Canada does not
     deal at arm's length is a specified financial institution when a dividend
     is paid on an Exchangeable Share, then dividends received or deemed to be
     received by a shareholder that is a corporation may not be deductible in
     computing taxable income but, instead, may be fully included in taxable
     income under Part I of the Canadian Tax Act. Pioneer Canada has informed
     Canadian tax counsel that it is of the view that neither it nor any person
     with whom it does not deal at arm's length is a specified financial
     institution at the current time, but there can be no assurances that this
     status will not change prior to any dividend which is received or deemed to
     be received by a corporate shareholder.
 
     The Exchangeable Shares will be "taxable preferred shares" and "short-term
preferred shares" for purposes of the Canadian Tax Act. Accordingly, Pioneer
Canada will be subject to a 66 2/3% tax under Part VI.1 of the Canadian Tax Act
on dividends, other than excluded dividends, paid or deemed to be paid on the
Exchangeable Shares. Dividends received or deemed to be received on the
Exchangeable Shares will not be subject to the 10% tax under Part IV.1 of the
Canadian Tax Act applicable to certain corporations.
 
     In the event the United States Internal Revenue Service (the "IRS") imposes
U.S. withholding tax with respect to dividends paid on the Exchangeable Shares
as set out in "-- United States Federal Income Tax Considerations -- Non-U.S.
Holders -- Dividends," it is unlikely that a Canadian resident Pioneer Canada
Shareholder will be entitled to a foreign tax credit in Canada with respect to
such U.S. withholding tax.
 
     Redemption or Exchange of Exchangeable Shares. The disposition of an
Exchangeable Share for a share of Pioneer Common Stock will be a taxable
transaction. A disposition can occur as a redemption by Pioneer
                                       17
<PAGE>   19
 
Canada or as an acquisition by Pioneer. The Canadian federal income tax
consequences of a redemption differ from those of an acquisition. A holder
exercising the right of retraction in respect of an Exchangeable Share cannot
control whether the share will be acquired by Pioneer under the Retraction Call
Right or redeemed by Pioneer Canada if the Retraction Call Right is not
exercised; however, a holder who exercises the right of retraction will be
notified if the Retraction Call Right will not be exercised by Pioneer and the
holder may cancel the Retraction Request and retain the Exchangeable Share.
 
     The following explains the tax treatment to a holder of an Exchangeable
Share on a redemption by Pioneer Canada or an acquisition by Pioneer.
 
     (a) Redemption of Exchangeable Shares by Pioneer Canada. On a redemption
(including a retraction) of an Exchangeable Share by Pioneer Canada, a portion
of the redemption proceeds may be deemed to be a dividend received by the
holder. The deemed dividend is calculated as the amount, if any, by which the
redemption proceeds exceeds the paid-up capital at that time of the Exchangeable
Share. The deemed dividend is subject to the tax treatment accorded to dividends
described above. Pioneer Canada is required to calculate the deemed dividend and
report the amount to the holder of the Exchangeable Share. The holder of the
Exchangeable Share may also have a capital gain or capital loss as a result of
the redemption to the extent that the proceeds of disposition of the
Exchangeable Share, less any reasonable cost of disposition, exceed (or are less
than) the adjusted cost base to the holder of the Exchangeable Share. The holder
of the Exchangeable Share is considered to have disposed of the Exchangeable
Share for proceeds of disposition equal to the redemption proceeds less the
amount of the deemed dividend. In the case of a shareholder that is a
corporation, in some circumstances the amount of any deemed dividend may be
treated as proceeds of disposition, and not as a dividend, for purposes of
calculating a capital gain. Three-quarters of any capital gain (referred to in
the Canadian Tax Act as a "taxable capital gain") must be included in income and
three-quarters of any capital loss (referred to in the Canadian Tax Act as an
"allowable capital loss") may generally be used to offset taxable capital gains
in the year the loss arises, in any of the three prior years or in any
subsequent year.
 
     A Pioneer Canada Shareholder that is throughout the relevant taxation year
a "Canadian-controlled private corporation" (as defined in the Canadian Tax Act)
may be liable to pay an additional refundable tax of 6 2/3% on its "aggregate
investment income" for the year, which is defined to include taxable capital
gains (but not dividends or deemed dividends deductible in computing taxable
income).
 
     If a Pioneer Canada Shareholder is a corporation, the amount of any capital
loss arising from a disposition of Exchangeable Shares may be reduced by the
amount of dividends received or deemed to have been received by it on the
Exchangeable Shares previously owned by such holder, to the extent and under
circumstances prescribed by the Canadian Tax Act. Similar rules may apply where
a corporation is a member of a partnership or a beneficiary of a trust that owns
Exchangeable Shares or where a trust or partnership of which a corporation is a
beneficiary or a member is a member of a partnership or a beneficiary of a trust
that owns Exchangeable Shares.
 
     Capital gains realized by a Pioneer Canada Shareholder who is an individual
may be subject to an alternative minimum tax. The Canadian Tax Act provides that
the tax payable by individuals (other than certain trusts) is the greater of the
tax otherwise determined and an alternative minimum tax. For purposes of
computing the alternative minimum tax, one-quarter of all capital gains are
added back to the individual's income as otherwise determined.
 
     (b) Acquisition of Exchangeable Shares by Pioneer. On the acquisition of an
Exchangeable Share by Pioneer, the holder will in general realize a capital gain
(or a capital loss) equal to the amount by which the proceeds of disposition of
the Exchangeable Share, less any reasonable cost of disposition, exceed (or are
less than) the adjusted cost base to the holder of the Exchangeable Share. A
holder will be required to include in income any such capital gain or capital
loss in the manner and subject to the rules described above. The acquisition of
an Exchangeable Share by Pioneer will not result in a deemed dividend to the
holder of the Exchangeable Share.
 
                                       18
<PAGE>   20
 
     The redemption proceeds in the case of a redemption by Pioneer Canada and
the proceeds of disposition in the case of an acquisition by Pioneer will be the
fair market value of a share of Pioneer Common Stock at the time of the
disposition plus the amount of all declared but unpaid dividends on the
Exchangeable Share.
 
     The cost base of a share of Pioneer Common Stock received on the
retraction, redemption or exchange of an Exchangeable Share will be equal to the
fair market value of the share of Pioneer Common Stock at the time of such
event.
 
     The following example illustrates the different treatment for a redemption
by Pioneer Canada and an acquisition by Pioneer, assuming hypothetically that
the fair market value of the Pioneer Common Stock at the time of an exchange is
$50.00, the Exchangeable Shares have a paid-up capital at that time of $5.00 per
share and the adjusted cost base to the holder of the Exchangeable Share is
$10.00.
 
<TABLE>
<CAPTION>
                                                              REDEMPTION    ACQUISITION
                                                              ----------    -----------
<S>                                                           <C>           <C>
Exchange Consideration......................................    $50.00        $50.00
Deemed Dividend(a)..........................................     45.00           (b)
Proceeds of Disposition for capital gains purposes..........      5.00         50.00
Adjusted Cost Base..........................................     10.00         10.00
                                                                ------        ------
Capital Gain (Capital Loss)(a)..............................    $(5.00)       $40.00
                                                                ======        ======
</TABLE>
 
- ---------------
 
(a) These line items (being the deemed dividend and the capital gain (or capital
    loss)) must be reported by the former holder of the Exchangeable Share.
 
(b) There is no deemed dividend in the case of an acquisition of the
    Exchangeable Shares by a person other than Pioneer Canada.
 
     Dividends on Pioneer Common Stock. Dividends paid on shares of Pioneer
Common Stock will be included in the recipient's income for the purposes of the
Canadian Tax Act. Such dividends received by an individual shareholder will not
be subject to the gross-up and dividend tax credit rules in the Canadian Tax
Act. A corporation which is a shareholder will include such dividends in
computing its taxable income. United States withholding tax on such dividends
will be eligible for foreign tax credit or deduction treatment where applicable
under the Canadian Tax Act. Special considerations may also apply to the receipt
of dividends by a Canadian resident corporate shareholder at a time when Pioneer
is a "foreign affiliate" of the shareholder within the meaning of the Canadian
Tax Act.
 
     Disposition of Pioneer Common Stock. A disposition or deemed disposition of
a share of Pioneer Common Stock by a holder will generally result in a capital
gain (or capital loss) equal to the amount by which the proceeds of disposition,
net of any reasonable costs of disposition, exceed (or are less than) the
adjusted cost base to the holder of the share. Such holders will be required to
include in income any such capital gain or capital loss in the manner and
subject to the rules described above.
 
  Eligibility for Investment
 
     Qualified Investments. Provided the Exchangeable Shares and the shares of
Pioneer Common Stock are listed on a prescribed stock exchange (which currently
includes the TSE and the NYSE), such securities will be qualified investments
under the Canadian Tax Act for trusts governed by registered retirement savings
plans, registered retirement income funds and deferred profit sharing plans. The
Voting Rights and Exchange Rights will not be qualified investments under the
Canadian Tax Act. However, Pioneer Canada is of the view that the fair market
value of these rights is nominal.
 
     Foreign Property. Provided the Exchangeable Shares are listed on a
prescribed stock exchange in Canada (which currently includes the TSE) and
Pioneer Canada continues to maintain a substantial presence in Canada, the
Exchangeable Shares will not be foreign property under the Canadian Tax Act for
trusts governed by registered pension plans, registered retirement savings
plans, registered retirement income funds and deferred profit sharing plans or
for certain other tax-exempt persons. Pioneer Canada will be considered to
 
                                       19
<PAGE>   21
 
have a substantial presence in Canada if it satisfies certain asset tests or if
it maintains an office in Canada and Pioneer Canada, or a corporation controlled
by it, employs more than five employees in Canada full time in the active
conduct of a business, other than an investment activity or a business carried
on through a partnership of which the corporation is not a majority interest
partner. Pioneer Canada has informed Canadian tax counsel that following the
Arrangement, Pioneer Canada will satisfy this substantial presence test and
expects that it will continue to satisfy the test.
 
     The shares of Pioneer Common Stock will be foreign property under the
Canadian Tax Act as will the Voting Rights and Exchange Rights.
 
  Pioneer Canada Shareholders Not Resident in Canada
 
     The following portion of the summary is applicable to Pioneer Canada
Shareholders who, for purposes of the Canadian Tax Act, have not been and will
not be resident or deemed to be resident in Canada at any time while they have
held Exchangeable Shares or will hold shares of Pioneer Common Stock and to whom
such shares are not "taxable Canadian property" and, in the case of a
non-resident of Canada who carries on an insurance business in Canada and
elsewhere, the shares are not effectively connected with its Canadian insurance
business.
 
     Pioneer Canada Shareholders not resident in Canada were not entitled to
receive Exchangeable Shares pursuant to the Plan of Arrangement, and it is not
expected that a Pioneer Canada Shareholder not resident in Canada would, in
general, wish to acquire Exchangeable Shares on the trading markets after their
original issuance. Accordingly, this portion of the summary is expected to have
limited applicability.
 
     A holder of Exchangeable Shares will not be subject to tax under the
Canadian Tax Act on the exchange of an Exchangeable Share for a share of Pioneer
Common Stock, except to the extent the exchange gives rise to a deemed dividend
(as described above for Canadian residents), or on the sale or other disposition
of an Exchangeable Share or a share of Pioneer Common Stock, unless the shares
constitute "taxable Canadian property" to the holder (within the meaning of the
Canadian Tax Act). Generally, the Exchangeable Shares and shares of Pioneer
Common Stock will not be taxable Canadian property provided that such shares are
listed on a prescribed stock exchange (which currently includes the TSE and the
NYSE), the holder does not use or hold, and is not deemed to use or hold, the
Exchangeable Shares or the shares of Pioneer Common Stock, as applicable, in
connection with carrying on a business in Canada and the holder, persons with
whom such holder does not deal at arm's length, or the holder and such persons,
has not owned (or had under option) 25% or more of the issued shares of any
class or series of the capital stock of Pioneer Canada or Pioneer at any time
within five years preceding the date in question. In the case of Pioneer, even
if the holder exceeds the 25% threshold with respect to shares of Pioneer Common
Stock, any gain on the sale or other disposition of such shares may not be
taxable in Canada, and such holders should consult their own tax advisors. The
Exchangeable Shares are listed on the TSE, and Pioneer has indicated that it
intends to use its best efforts to cause Pioneer Canada to maintain such
listing.
 
     Any dividends paid on the Exchangeable Shares will be subject to
non-resident withholding tax under the Canadian Tax Act at the rate of 25%,
although such rate may be reduced under the provisions of an applicable income
tax treaty. For example, under the Tax Treaty, the rate is generally reduced to
15% for dividends paid to a person who is resident in the United States for
purposes of the Tax Treaty.
 
UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS
 
     This section summarizes the material United States federal income tax
considerations generally applicable to Pioneer Canada Shareholders of owning and
disposing of Exchangeable Shares (and Pioneer Common Stock received in exchange
therefor), but it does not purport to be a complete analysis of all of the
potential tax effects thereof.
 
     This summary is based on United States federal income tax law currently in
effect. The legal conclusions contained herein represent the opinion of Vinson &
Elkins L.L.P., United States counsel to Pioneer Canada. No statutory, judicial
or administrative authority exists which directly addresses certain of the
United States
 
                                       20
<PAGE>   22
 
federal income tax consequences of the ownership of instruments comparable to
the Exchangeable Shares. Consequently, some aspects of the United States federal
income tax treatment of the holding and exchange of Exchangeable Shares for
shares of Pioneer Common Stock are not certain. No advance income tax ruling has
been sought or obtained from the United States Internal Revenue Service (the
"IRS") regarding the tax consequences of the transactions described herein, and
there can be no assurance that the IRS will not successfully challenge certain
of the conclusions reached in this discussion, particularly those as to which
uncertainty is indicated.
 
     Except as specifically stated otherwise, the discussion does not address
state, local, or foreign taxes or federal tax aspects other than United States
federal income taxation under the Internal Revenue Code of 1986, as amended (the
"U.S. Code"), nor does it address all aspects of such tax that may be applicable
to the specific circumstances of a particular Pioneer Canada Shareholder. The
discussion may not apply to Pioneer Canada Shareholders that are subject to
special provisions of the U.S. Code, such as tax-exempt organizations, financial
institutions, insurance companies, broker-dealers, persons having a "functional
currency" other than the United States dollar, and Pioneer Canada Shareholders
who hold Exchangeable Shares as part of a straddle, wash sale, hedging or
conversion transaction (other than by virtue of their participation in the
Arrangement).
 
     WHILE THIS SUMMARY IS INTENDED TO ADDRESS ALL PRINCIPAL UNITED STATES
FEDERAL INCOME TAX CONSIDERATIONS, IT IS OF A GENERAL NATURE ONLY AND IS NOT
INTENDED TO BE, NOR SHOULD IT BE CONSTRUED AS, LEGAL OR TAX ADVICE TO ANY
PARTICULAR PIONEER CANADA SHAREHOLDER. THEREFORE, EACH PIONEER CANADA
SHAREHOLDER IS URGED TO CONSULT WITH A TAX ADVISOR WITH RESPECT TO ITS
PARTICULAR CIRCUMSTANCES AS SUCH MAY AFFECT THE UNITED STATES FEDERAL, STATE AND
LOCAL TAX CONSEQUENCES AND THE FOREIGN TAX CONSEQUENCES OF THE ACQUISITION,
OWNERSHIP AND DISPOSITION OF EXCHANGEABLE SHARES AND PIONEER COMMON STOCK
RECEIVED IN EXCHANGE THEREFOR. NO ADVANCE INCOME TAX RULING HAS BEEN OBTAINED
FROM THE IRS TO CONFIRM THE TAX CONSEQUENCES OF ANY OF THE TRANSACTIONS
DESCRIBED HEREIN.
 
  Non-U.S. Holders
 
     General. This subsection is addressed to Pioneer Canada Shareholders that
(i) are Non-U.S. Holders (as defined below), and (ii) will hold Exchangeable
Shares (and Pioneer Common Stock received in exchange therefor) as capital
assets. For purposes of the foregoing, the term "Non-U.S. Holder" means a
nonresident alien individual, or a foreign corporation, a foreign partnership or
a foreign estate or trust which is other than a U.S. Holder (as defined below).
An individual may, subject to certain exceptions, be deemed to be a resident
alien (as opposed to a nonresident alien) by virtue of being present in the
United States for at least 31 days in the calendar year and for an aggregate of
at least 183 days during a three-year period ending in the current calendar year
(counting for such purposes all of the days present in the calendar year,
one-third of the days present in the immediately preceding year, and one-sixth
of the days present in the second preceding year). Resident aliens are subject
to tax as if they were U.S. citizens.
 
     It is expected that most Pioneer Canada Shareholders who, for purposes of
the Canadian Tax Act, are resident or deemed to be resident in Canada will be
Non-U.S. Holders. A Non-U.S. Holder seeking benefits under an applicable tax
treaty or an exemption from U.S. withholding tax for "effectively connected
income," as described below, may be required to comply with additional
certification and other requirements in order to establish his entitlement to
such benefits or exemption. This discussion does not consider U.S. tax
consequences that may be relevant to a Non-U.S. Holder who is a United States
expatriate or who has other special facts and circumstances.
 
     Dividends. Neither Pioneer Canada nor Pioneer intends to withhold any
amount for U.S. withholding tax on dividends paid to Non-U.S. Holders of
Exchangeable Shares. There is some possibility, however, that the IRS may
successfully assert that U.S. withholding tax is payable with respect to such
dividends.
 
                                       21
<PAGE>   23
 
     Dividends received by a Non-U.S. Holder with respect to Pioneer Common
Stock that are not effectively connected with the conduct of a trade or business
in the United States will generally be subject to U.S. withholding tax. The U.S.
withholding tax rate is 30% unless reduced by treaty. Under the Tax Treaty, the
rate currently is 15%, generally, on dividends paid to residents of Canada.
 
     Gain on Dispositions. A Non-U.S. Holder generally will not be subject to
U.S. tax on any gain recognized on the receipt, sale or other disposition of the
Exchangeable Shares, the exchange of the Exchangeable Shares for Pioneer Common
Stock, or the sale or other disposition of such Pioneer Common Stock, unless (a)
such gain is effectively connected with a trade or business in the United
States, or, if a tax treaty applies, is attributable to a permanent
establishment maintained by the Non-U.S. Holder in the United States, or (b) the
Non-U.S. Holder is an individual who is present in the United States for 183
days or more in the taxable year of disposition, and certain other conditions
are satisfied. In this connection, any Non-U.S. Holder who at any time actually
and constructively owns more than 5% of either the Exchangeable Shares or the
Pioneer Common Stock should be aware that Pioneer is probably a "United States
real property holding corporation" within the meaning of section 897 of the U.S.
Code, and therefore such Non-U.S. Holder should seek advice whether his gain or
loss would be deemed to be effectively connected with a U.S. business.
 
     U.S. Estate Tax. Pioneer Common Stock held by an individual Non-U.S. Holder
at the time of death will be deemed to be a U.S. situs asset for purposes of
U.S. estate tax law and therefore will generally be subject to the U.S. estate
tax, except as may otherwise be provided by an applicable tax or estate tax
treaty with the United States. No opinion is expressed as to the situs of
Exchangeable Shares for purposes of U.S. estate tax law.
 
  U.S. Holders
 
     General. This subsection is addressed to Pioneer Canada Shareholders that
(i) are U.S. Holders (as defined below) and (ii) hold Exchangeable Shares (and
Pioneer Common Stock received in exchange therefor) as capital assets. For
purposes of the foregoing, the term "U.S. Holder" means (a) a citizen or
individual resident of the United States, (b) a corporation or partnership
created or organized in or under the laws of the United States or any state
thereof, (c) an estate the income of which is includible in its gross income for
United States federal income tax purposes without regard to its source, or (d) a
trust as to which a court in the United States is able to exercise primary
supervision over the administration of the trust and one or more United States
fiduciaries have the authority to control all substantial decisions of the
trust.
 
     U.S. Holders of Chauvco Stock are not entitled to receive Exchangeable
Shares pursuant to the Plan of Arrangement, and it is not expected that a U.S.
Holder would, in general, wish to acquire Exchangeable Shares on the trading
markets after their original issuance. Accordingly, this subsection is expected
to have limited applicability.
 
     Ownership and Disposition of Exchangeable Shares. Assuming that Pioneer
Canada is not a PFIC (as defined in the following paragraphs of this
subsection), dividends paid to a U.S. Holder with respect to Exchangeable Shares
generally will constitute ordinary dividend income to the extent paid out of
Pioneer Canada's earnings and profits as determined under U.S. tax principles.
The amount of a dividend paid in non-U.S. currency will be calculated by
reference to the exchange rate in effect on the date the dividend is
distributed. Foreign currency gain or loss may be realized on any currency
received that is not converted into United States dollars on such date.
Dividends will generally be treated as foreign source passive income for foreign
tax credit limitation purposes. Any foreign tax imposed on such dividends will
generally be allowable either as a credit against the holder's United States
federal income tax liability (subject to applicable limitations) or as a
deduction in computing U.S. taxable income. Gain or loss recognized on the
disposition of Exchangeable Shares will generally be treated as U.S. source for
foreign tax credit limitation purposes.
 
     Exchange of Exchangeable Shares. A U.S. Holder that exercises such holder's
right to exchange its Exchangeable Shares for shares of Pioneer Common Stock
will generally recognize gain or loss on such exchange, subject to the
discussion below. Such gain or loss will be equal to the difference between the
fair market value of the shares of Pioneer Common Stock received, as determined
at the time of the exchange, and the U.S. Holder's tax basis in the Exchangeable
Shares surrendered. The gain or loss will generally be capital
                                       22
<PAGE>   24
 
gain or loss, except that, with respect to any declared but unpaid dividends on
the Exchangeable Shares, ordinary income may be recognized. A U.S. Holder will
generally, subject to the discussion below, have a tax basis in the shares of
Pioneer Common Stock received equal to the fair market value of such shares at
the time of the exchange. The holding period for such shares will generally,
subject to the discussion below, begin on the day after the exchange. The IRS
could assert, however, that the Exchangeable Shares and certain of the rights
associated therewith constitute "offsetting positions" for purposes of the
straddle rules set forth in Section 1092 of the U.S. Code. In such case, the
holding period of the Exchangeable Shares would not increase while held by a
U.S. Holder.
 
     It is possible, however, that a U.S. Holder who holds Exchangeable Shares
not acquired in the Arrangement would not be permitted to recognize loss on an
exchange of such Exchangeable Shares for Pioneer Common Stock. In that case, the
U.S. Holder will have a tax basis in the shares of Pioneer Common Stock received
equal to the tax basis of the Exchangeable Shares exchanged therefor, and the
U.S. Holder's holding period for the Pioneer Common Stock received will include
the U.S. Holder's holding period in the Exchangeable Shares exchanged therefor.
 
     Under the Taxpayer Relief Act of 1997 (the "1997 Act"), the maximum capital
gains rate for individuals has been reduced to 20% for capital assets held for
more than 18 months before disposition, but the rate applicable to gain realized
on the exchange of Exchangeable Shares by a U.S. Holder will depend upon the
holding period of such Exchangeable Shares, the holder's other taxable income,
and other factors.
 
     For U.S. foreign tax credit purposes, any gain realized by a U.S. Holder
will generally be treated as U.S. source, except that, if under the Tax Treaty
any Canadian tax is imposed on the exchange, the gain could be treated as
Canadian source at the election of the U.S. Holder. As a result of such
election, the Canadian tax would generally be available as a credit (subject to
applicable limitations) against the U.S. tax attributable to such gain. A U.S.
Holder that is ineligible for a foreign tax credit with respect to any tax paid
may be entitled to a deduction therefor in computing United States taxable
income.
 
     Under certain limited circumstances, an exchange by a U.S. Holder of
Exchangeable Shares for shares of Pioneer Common Stock may be characterized as a
tax-free exchange. In order to be so characterized, however, certain
requirements must be satisfied as of the date of the exchange. Whether such
requirements can be satisfied will depend on facts and circumstances existing at
that time and which cannot be accurately predicted as of the date of this
Prospectus. Moreover, there is no direct authority as to the proper treatment
for United States federal income tax purposes of the exchange of Exchangeable
Shares for shares of Pioneer Common Stock. For these reasons, there can be no
assurance that an exchange of Exchangeable Shares for Pioneer Common Stock
should properly be treated as tax free under any circumstances. If, however,
such exchange did qualify as a tax-free exchange, a U.S. Holder's tax basis in
the shares of Pioneer Common Stock received would be equal to such holder's tax
basis in the Exchangeable Shares exchanged therefor, and the holding period of
the shares of Pioneer Common Stock received by such U.S. Holder should include
the holding period of the Exchangeable Share exchanged therefor.
 
     Passive Foreign Investment Company Considerations. For United States
federal income tax purposes, Pioneer Canada generally will be treated as a
passive foreign investment company (a "PFIC") for any taxable year ending after
the consummation of the Arrangement during which either (i) 75 percent or more
of its gross income was passive income (as defined for United States federal
income tax purposes) or (ii) on average for such taxable year, 50 percent or
more of its assets (measured as described below) produced or were held for the
production of passive income. For purposes of applying the foregoing tests, the
assets and gross income of Pioneer Canada's significant subsidiaries will be
attributed to Pioneer Canada.
 
     For purposes of applying the 50% assets test, and in the absence of
regulations affording an exception to securities listed for trading on the TSE,
Pioneer Canada's assets must be measured by their adjusted tax bases (as
calculated in order to compute earnings and profits for United States federal
income tax purposes), subject to certain adjustments. As a result, it is
possible that Pioneer Canada could be a PFIC even though less than 50% of
Pioneer Canada's assets (measured by the fair market value of such assets) do
not constitute passive assets.
 
                                       23
<PAGE>   25
 
     Pioneer and Pioneer Canada intend to endeavor to cause Pioneer Canada to
avoid PFIC status in the future, although there can be no assurance that they
will be able to do so or that their intent will not change. Moreover, in
connection with the transactions contemplated herein, no opinion will be deemed
given regarding Pioneer Canada's status as a PFIC. After the Arrangement,
Pioneer Canada will endeavor to notify U.S. Holders of Exchangeable Shares if it
believes that Pioneer Canada was a PFIC for that taxable year.
 
     If a corporation is a PFIC at any time in which a U.S. Holder owns its
shares and has not elected ("QEF Election") to treat the corporation as a
qualified electing fund, the gain recognized on the disposition of such shares
is taxed as ordinary income at rates that might be higher than those otherwise
applicable, and an interest charge is imposed on such gain. The general effect
of a QEF election is to require the U.S. Holder's pro rata share of the
corporation's income for each taxable year in which the corporation is
classified as a PFIC to be included in his taxable income, even if no dividend
distributions are received. The holder, however, can also elect to defer payment
of the taxes on such income, subject to an interest charge, until the shares are
transferred or a distribution on such shares is received. In addition, it is
possible that under the 1997 Act a U.S. Holder will be permitted, beginning in
1998, to make a mark-to-market election with respect to shares of a PFIC in lieu
of incurring the special tax and interest charge on disposition of those shares.
 
     The foregoing summary of the possible application of the PFIC rules to
Pioneer Canada and the U.S. Holders of Exchangeable Shares is only a summary of
certain material aspects of those rules. Because the United States federal
income tax consequences to such U.S. Holders under the PFIC provisions are
significant and complex, such U.S. Holders are urged to discuss these
consequences with their tax advisors.
 
                                 LEGAL MATTERS
 
     Certain legal matters in connection with the shares of Pioneer Common Stock
offered hereby will be passed upon for Pioneer by Vinson & Elkins L.L.P.,
Dallas, Texas. Certain federal Canadian and U.S. tax matters will be passed upon
for Pioneer by MacKimmie Matthews, Calgary, Canada, and Vinson & Elkins L.L.P.,
Dallas, Texas, as set forth under "Income Tax Considerations." Michael D.
Wortley, a partner in the law firm of Vinson & Elkins L.L.P., is a director of
Pioneer and beneficially owns 6,623 shares of Pioneer Common Stock.
 
                                    EXPERTS
 
     The Consolidated Financial Statements of Pioneer (successor to Parker &
Parsley and subsidiaries) have been incorporated by reference in this
Registration Statement in reliance upon the report of KPMG Peat Marwick LLP,
independent certified public accountants, and upon the authority of said firm as
experts in accounting and auditing. The report of KPMG Peat Marwick LLP refers
to a change in the method of accounting for the impairment of long-lived assets
and for long-lived assets to be disposed of in 1995 and a change in the method
of accounting for income taxes in 1993.
 
     The Consolidated Financial Statements of Mesa incorporated by reference in
this Registration Statement have been audited by Arthur Andersen LLP,
independent public accountants, as indicated in their report with respect
thereto, and are incorporated by reference herein in reliance upon the authority
of said firm as experts in giving said report.
 
     The Financial Statements of Greenhill Petroleum Corporation incorporated by
reference in this Registration Statement, have been incorporated herein in
reliance on the report of Coopers & Lybrand L.L.P., independent accountants,
given on authority of that firm as experts in accounting and auditing.
 
     The Consolidated Financial Statements of Chauvco incorporated by reference
in this Registration Statement have been audited by Price Waterhouse, chartered
accountants, as indicated in their report with respect thereto, and are
incorporated by reference herein in reliance upon the authority of said firm as
experts in giving said report.
 
     The estimates of proved reserves of Pioneer (successor to Parker & Parsley
and subsidiaries) as of December 31, 1996, incorporated by reference in this
Registration Statement are based upon a reserve report
                                       24
<PAGE>   26
 
prepared by Pioneer and audited by Netherland, Sewell & Associates, Inc.,
independent petroleum consultants, and are incorporated by reference herein upon
the authority of such firm as experts with respect to such matters covered by
such report.
 
     The estimates of Mesa's proved reserves as of December 31, 1996,
incorporated by reference in this Registration Statement with respect to its
Hugoton and West Panhandle field properties are based upon a reserve report
prepared by Williamson Petroleum Consultants, Inc., independent petroleum
consultants, and are incorporated by reference herein upon the authority of such
firm as experts with respect to such matters covered by such report. The
estimates of Greenhill Petroleum Corporation's proved reserves as of December
31, 1996, incorporated by reference in this Registration Statement pursuant to
items 9 and 14 under the section entitled "Incorporation of Certain Documents By
Reference" in this Registration Statement, are based upon a reserve report
prepared by Miller and Lents, Ltd., independent petroleum consultants, and are
incorporated by reference herein upon the authority of such firm as experts with
respect to such matters covered by such report.
 
     The estimates of Chauvco's proved reserves as of December 31, 1996,
incorporated by reference in this Registration Statement are based upon reserve
reports prepared by Gilbert Lausten Jung Associates, Ltd. and Martin Petroleum
and Associates, independent petroleum consultants, and are incorporated by
reference herein upon the authority of such firm as experts with respect to such
matters covered by such report.
 
                                       25
<PAGE>   27
 
             ======================================================
 
     NO PERSON HAS BEEN AUTHORIZED TO GIVE ANY INFORMATION OR TO MAKE ANY
REPRESENTATIONS OTHER THAN THOSE CONTAINED IN THIS PROSPECTUS OR IN A PROSPECTUS
SUPPLEMENT, AND IF GIVEN OR MADE, SUCH INFORMATION OR REPRESENTATIONS MUST NOT
BE RELIED UPON AS HAVING BEEN AUTHORIZED BY PIONEER OR ANY OTHER PERSON. NEITHER
THIS PROSPECTUS NOR ANY PROSPECTUS SUPPLEMENT CONSTITUTES AN OFFER TO SELL OR A
SOLICITATION OF ANY OFFER TO BUY ANY SECURITIES OTHER THAN THE SECURITIES TO
WHICH IT RELATES, NOR DOES IT CONSTITUTE AN OFFER TO SELL OR A SOLICITATION OF
ANY OFFER TO BUY THE SECURITIES IN ANY JURISDICTION IN WHICH THE OFFER OR
SOLICITATION IS NOT AUTHORIZED, OR IN WHICH THE PERSON MAKING THE OFFER OR
SOLICITATION IS NOT QUALIFIED TO DO SO, OR TO ANY PERSON TO WHOM IT IS UNLAWFUL
TO MAKE THE OFFER OR SOLICITATION. NEITHER THE DELIVERY OF THIS PROSPECTUS NOR
ANY PROSPECTUS SUPPLEMENT NOR ANY SALE MADE HEREUNDER OR THEREUNDER SHALL, UNDER
ANY CIRCUMSTANCES, CREATE ANY IMPLICATION THAT ANY INFORMATION CONTAINED HEREIN
OR THEREIN IS CORRECT AS OF ANY TIME SUBSEQUENT TO THE DATE HEREOF.
 
                             ---------------------
 
                               TABLE OF CONTENTS
 
<TABLE>
<CAPTION>
                                         PAGE
                                         ----
<S>                                      <C>
Available Information..................    2
Incorporation of Certain Documents by
  Reference............................    2
Risk Factors...........................    3
Pioneer................................    4
Use of Proceeds........................    4
Description of Capital Stock...........    4
Plan of Distribution...................   13
Income Tax Considerations..............   16
Legal Matters..........................   24
Experts................................   24
</TABLE>
 
             ======================================================
 
             ======================================================
 
                               10,901,924 SHARES
 
                                PIONEER NATURAL
                               RESOURCES COMPANY
 
                                  COMMON STOCK
                             ---------------------
 
                                   PROSPECTUS
                             ---------------------
 
                               FEBRUARY 13, 1998
 
             ======================================================
<PAGE>   28
 
                                    PART II
 
                     INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 14. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION.
 
     The following table sets forth those expenses to be incurred by the
Registrant, Pioneer Natural Resources Company (the "Company"), in connection
with the issuance and distribution of the securities being registered. Except
for the Securities and Exchange Commission registration fee, all amounts shown
are estimates.
 
<TABLE>
<S>                                                           <C>
Securities and Exchange Commission registration fee.........  $      0
Accounting fees and expenses................................     5,000
Legal fees and expenses.....................................    15,000
Transfer agent's fees and expenses..........................    10,000
Blue Sky fees and expenses, including counsel fees..........     1,000
Fees of rating agencies.....................................         0
Listing fees................................................    10,000
Printing and engraving expenses.............................    60,000
Miscellaneous...............................................    10,000
                                                              --------
          Total.............................................  $111,000
                                                              ========
</TABLE>
 
ITEM 15. INDEMNIFICATION OF DIRECTORS AND OFFICERS.
 
     Article Twelfth of the Restated Certificate of Incorporation of the
Registrant provides that the Registrant must indemnify its officers and
directors to the extent allowed by the Delaware General Corporation Law.
Pursuant to Section 145 of the Delaware General Corporation Law, the Registrant
generally has the power to indemnify its present and former directors and
officers against expenses and liabilities incurred by them in connection with
any suit to which they are, or are threatened to be made, a party by reason of
their serving in those positions so long as they acted in good faith and in a
manner they reasonably believed to be in, or not opposed to, the best interests
of the Registrant, and with respect to any criminal action, they had no
reasonable cause to believe their conduct was unlawful. With respect to suits by
or in the right of the Registrant, however, indemnification is generally limited
to attorneys' fees and other expenses and is not available if the person is
adjudged to be liable to the Registrant unless the court determines that
indemnification is appropriate. The statute expressly provides that the power to
indemnify authorized thereby is not exclusive of any rights granted under any
by-law, agreement, vote of stockholders or disinterested directors, or
otherwise. The Registrant also has the power to purchase and maintain insurance
for its directors and officers. Additionally, Article Twelfth of the Restated
Certificate of Incorporation provides that, in the event that an officer or
director files suit against the Registrant seeking indemnification of
liabilities or expenses incurred, the burden will be on the Registrant to prove
that the indemnification would not be permitted under the Delaware General
Corporation Law.
 
     The Registrant has entered into Indemnification Agreements with each of its
directors and officers. These agreements provide that the Registrant must
indemnify an officer or director for liabilities incurred to the fullest extent
permitted by the Delaware General Corporation Law. The Registrant must, within
ten days of a request, indemnify an officer or director for expenses incurred in
the defense of a claim or other proceeding. The obligation of the Registrant to
provide the indemnification does not apply if, before the date on which the
Registrant must provide the indemnification, the Registrant's Board of
Directors, or a representative chosen by the Board of Directors, concludes that
indemnification would be improper under the Delaware General Corporation Law.
 
     The preceding discussion of the Registrant's Restated Certificate of
Incorporation, Section 145 of the Delaware General Corporation Law, and the
Indemnification Agreements is not intended to be exhaustive and is qualified in
its entirety by the Restated Certificate of Incorporation, Section 145 of the
Delaware General Corporation Law, and the Indemnification Agreements.
 
                                      II-1
<PAGE>   29
 
ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES.
 
     There are filed with the Registration Statement the following exhibits:
 
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
          2.1            -- Amended and Restated Agreement and Plan of Merger, dated
                            as of April 6, 1997, by and among Mesa, Mesa Operating
                            Co. ("MOC"), MXP Reincorporation Corp. and Parker &
                            Parsley (incorporated by reference to Exhibit 2.1 to
                            Pioneer's Registration Statement on Form S-4, dated June
                            27, 1997, Registration No. 333-26951).
          2.2            -- Combination Agreement, dated as of September 3, 1997,
                            between Pioneer and Chauvco (incorporated by reference to
                            Exhibit 2.2 to Pioneer's Registration Statement on Form
                            S-3, Registration No. 333-42315, filed with the SEC on
                            December 15, 1997).
          2.3            -- Plan of Arrangement under Section 186 of the Business
                            Corporations Act (Alberta) (incorporated by reference to
                            Annex E to the Definitive Joint Management Information
                            Circular and Proxy Statement of Pioneer and Chauvco, File
                            No. 001-13245, filed with the SEC on November 17, 1997).
          2.4            -- Form of Support Agreement between Pioneer and Pioneer
                            Canada (incorporated by reference to Annex H to the
                            Definitive Joint Management Information Circular and
                            Proxy Statement of Pioneer and Chauvco, File No.
                            001-13245, filed with the SEC on November 17, 1997).
          2.5            -- Form of Voting and Exchange Trust Agreement among
                            Pioneer, Pioneer Canada and Montreal Trust Company of
                            Canada, as Trustee (incorporated by reference to Annex I
                            to the Definitive Joint Management Information Circular
                            and Proxy Statement of Pioneer and Chauvco, File No.
                            001-13245, filed with the SEC on November 17, 1997).
          2.6            -- Amended and Restated Shareholders Agreement, dated as of
                            September 3, 1997, by and among Pioneer and Guy J.
                            Turcotte (incorporated by reference to Exhibit 2.6 to
                            Pioneer's Registration Statement on Form S-3,
                            Registration No. 333-42315, filed with the SEC on
                            December 15, 1997).
          2.7            -- Shareholders Agreement, dated as of September 3, 1997, by
                            and among Pioneer, Chauvco, DNR-MESA Holdings, L.P.
                            ("DNR"), Scott D. Sheffield and I. Jon Brumley
                            (incorporated by reference to Exhibit 2.3 to Pioneer's
                            Current Report on Form 8-K, File No. 001-13245, filed
                            with the SEC on October 2, 1997).
          2.8            -- Shareholders Agreement, dated as of September 3, 1997, by
                            and among Pioneer, Trimac Corporation and Gendis Inc.
                            (incorporated by reference to Exhibit 2.4 to Pioneer's
                            Current Report on Form 8-K, File No. 001-13245, filed
                            with the SEC on October 2, 1997).
          3.1            -- Amended and Restated Certificate of Incorporation of
                            Pioneer (incorporated by reference to Exhibit 3.1 to
                            Pioneer's Registration Statement on Form S-4,
                            Registration No. 333-26951).
          3.2            -- Restated Bylaws of Pioneer (incorporated by reference to
                            Exhibit 3.2 to Pioneer's Registration Statement on Form
                            S-4, Registration No. 333-26951).
          3.3            -- Certificate of Designations of Special Preferred Voting
                            Stock (incorporated by reference to Exhibit 3.3 to
                            Pioneer's Registration Statement on Form S-3,
                            Registration No. 333-42315, filed with the SEC on
                            December 15, 1997).
          3.4            -- Terms and Conditions of Exchangeable Shares (incorporated
                            by reference to Annex F to the Definitive Joint
                            Management Information Circular and Proxy Statement of
                            Pioneer and Chauvco, File No. 001-13245, filed with the
                            SEC on November 17, 1997).
</TABLE>
 
                                      II-2
<PAGE>   30
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
          4.1            -- Form of Certificate of Common Stock, par value $.01 per
                            share, of Pioneer (incorporated by reference to Exhibit
                            4.1 to Pioneer's Registration Statement on Form S-4,
                            Registration No. 333-26951).
          5.1*           -- Opinion of Vinson & Elkins L.L.P. as to the legality of
                            the securities to be registered.
          8.1*           -- Opinion of MacKimmie Matthews regarding tax matters.
          8.2*           -- Opinion of Vinson & Elkins L.L.P. regarding tax matters.
          9.1            -- Shareholder Agreement, dated as of April 6, 1997, between
                            Mesa, Boone Pickens and Parker & Parsley (incorporated by
                            reference to Exhibit 2.4 of Mesa's Form 8-K filed April
                            8, 1997).
          9.2            -- Shareholders Agreement, dated as of April 6, 1997,
                            between DNR and Mesa (incorporated by reference to
                            Exhibit 2.2 of Mesa's Form 8-K filed April 8, 1997).
         10.1            -- Indenture, dated July 2, 1996, among Pioneer Natural
                            Resources USA, Inc. ("Pioneer USA") (formerly MOC), as
                            Issuer, Pioneer (Mesa's successor), as Guarantor, and
                            Harris Trust and Savings Bank, as Trustee, relating to
                            the 11 5/8% Senior Subordinated Discount Notes Due 2006
                            (incorporated by reference to Exhibit 4.17 of Mesa's Form
                            10-Q dated August 13, 1996).
         10.2            -- First Supplemental Indenture, dated as of April 15, 1997,
                            among Pioneer USA (formerly MOC), as Issuer, Mesa, the
                            subsidiary guarantors named therein, Pioneer, and Harris
                            Trust and Savings Bank, as Trustee, with respect to the
                            indenture identified above as Exhibit 10.1 (incorporated
                            by reference to Exhibit 10.1 to Pioneer's Quarterly
                            Report on Form 10-Q for the period ended September 30,
                            1997, File No. 001-13245).
         10.3            -- Second Supplemental Indenture, dated as of August 7,
                            1997, among Pioneer USA (formerly MOC), as Issuer, Mesa,
                            the subsidiary guarantors named therein, Pioneer, and
                            Harris Trust and Savings Bank, as Trustee, with respect
                            to the indenture identified above as Exhibit 10.1
                            (incorporated by reference to Exhibit 10.2 to Pioneer's
                            Quarterly Report on Form 10-Q for the period ended
                            September 30, 1997, File No. 001-13245).
         10.4            -- Indenture, dated July 2, 1996, among Pioneer USA
                            (formerly MOC), as Issuer, Pioneer (Mesa's successor), as
                            Guarantor, and Harris Trust and Savings Bank, as Trustee,
                            relating to 10 5/8% Senior Subordinated Notes Due 2006
                            (incorporated by reference to Exhibit 4.18 of Mesa's Form
                            10-Q, dated August 13, 1996).
         10.5            -- First Supplemental Indenture, dated as of April 15, 1997,
                            among Pioneer USA (formerly MOC), as Issuer, Mesa, the
                            subsidiary guarantors named therein, Pioneer, and Harris
                            Trust and Savings Bank, as Trustee, with respect to the
                            indenture identified above as Exhibit 10.4 (incorporated
                            by reference to Exhibit 10.3 to Pioneer's Quarterly
                            Report on Form 10-Q for the period ended September 30,
                            1997, File No. 001-13245).
         10.6            -- Second Supplemental Indenture, dated as of August 7,
                            1997, among Pioneer USA (formerly MOC), as Issuer, Mesa,
                            the subsidiary guarantors named therein, Pioneer, and
                            Harris Trust and Savings Bank, as Trustee, with respect
                            to the indenture identified above as Exhibit 10.4
                            (incorporated by reference to Exhibit 10.4 to Pioneer's
                            Quarterly Report on Form 10-Q for the period ended
                            September 30, 1997, File No. 001-13245).
</TABLE>
 
                                      II-3
<PAGE>   31
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.7            -- Indentures relating to $50,000,000 principal amount of
                            8 1/2% Convertible Subordinated Debentures due 2005 of
                            Dorchester Master Limited Partnership ($3,762,000
                            principal amount of which were outstanding and held by
                            non affiliates at December 31, 1996) and $100,000,000
                            principal amount of 9 1/2% Senior Notes due 2000 of
                            Bridge Oil (U.S.A.) Inc. ($2,063,000 principal amount of
                            which were outstanding at December 31, 1996) have been
                            omitted pursuant to Item 601(b)(4)(iii)(A) of Regulation
                            S-K. Pioneer hereby agrees to furnish a copy of the
                            indentures to the Securities and Exchange Commission upon
                            request (incorporated by reference to Parker & Parsley's
                            Form 10-K, dated December 31, 1996).
         10.8            -- Indenture, dated April 12, 1995, between Pioneer USA
                            (successor to Parker & Parsley), and The Chase Manhattan
                            Bank (National Association), as Trustee (incorporated by
                            reference to Exhibit 4.1 to Parker & Parsley's Current
                            Report on Form 8-K, dated April 12, 1995, File No.
                            1-10695).
         10.9            -- First Supplemental Indenture, dated as of August 7, 1997,
                            among Parker & Parsley, The Chase Manhattan Bank, as
                            Trustee, and Pioneer USA, with respect to the indenture
                            identified above as Exhibit 10.8 (incorporated by
                            reference to Exhibit 10.5 to Pioneer's Quarterly Report
                            on Form 10-Q for the period ended September 30, 1997,
                            File No. 001-13245).
         10.10           -- Form of 8 7/8% Senior Notes Due 2005, dated as of April
                            12, 1995, in the aggregate principal amount of
                            $150,000,000, together with Officers' Certificate dated
                            April 12, 1995, establishing the terms of the 8 7/8%
                            Senior Notes Due 2005 pursuant to the indenture
                            identified above as Exhibit 10.8 (incorporated by
                            reference to Exhibit 4.2 to Parker & Parsley's Quarterly
                            Report on Form 10-Q for the period ended June 30, 1995,
                            File No. 1-10695).
         10.11           -- Form of 8 1/4% Senior Notes due 2007, dated as of August
                            22, 1995, in the aggregate principal amount of
                            $150,000,000, together with Officers' Certificate, dated
                            August 22, 1995, establishing the terms of the 8 1/4%
                            Senior Notes due 2007 pursuant to the indenture
                            identified above as Exhibit 10.8 (incorporated by
                            reference to Exhibit 1.2 to Parker & Parsley's Current
                            Report on Form 8-K, dated August 17, 1995, File No.
                            1-10695).
         10.12           -- Agreement of Sale between Pioneer Corporation and Cabot
                            Corporation, dated August 29, 1984 (incorporated by
                            reference to Exhibit 10.5 to Pioneer Corporation's Form
                            10-K, dated December 31, 1985).
         10.13           -- Settlement Agreement, dated March 15, 1989, by and among
                            Mesa Operating Limited Partnership and Mesa Limited
                            Partnership, et al., Energas Company and the City of
                            Amarillo (incorporated by reference to Exhibit 10(k) to
                            Mesa Limited Partnership's Form 10-K, dated December 31,
                            1990).
         10.14           -- Gas Purchase Agreement, dated December 1, 1989, between
                            Williams Natural Gas Company and Mesa Operating Limited
                            Partnership acting on behalf of itself and as agent for
                            Mesa Midcontinent Limited Partnership (incorporated by
                            reference to Exhibit 10.1 to Registration Statement of
                            Mesa Limited Partnership on Form S-3, Registration No.
                            33-32978).
         10.15           -- "B" Contract Production Allocation Agreement, dated July
                            29, 1991, and effective as of January 1, 1991, between
                            Colorado Interstate Gas Company and Mesa Operating
                            Limited Partnership (incorporated by reference to Exhibit
                            10(r) to Mesa's Form 10-K, dated December 31, 1991).
         10.16           -- Amendment to "B" Contract Production Allocation Agreement
                            effective as of January 1, 1993, between Colorado
                            Interstate Gas Company and Mesa Operating Limited
                            Partnership (incorporated by reference to Exhibit 10.24
                            to Mesa's Registration Statement on Form S-1,
                            Registration No. 033-51909).
</TABLE>
 
                                      II-4
<PAGE>   32
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.17           -- Amended Peak Day Gas Purchase Agreement, dated effective
                            June 19, 1991, between Colorado Interstate Gas Company
                            and Mesa Operating Limited Partnership (incorporated by
                            reference to Exhibit 10(t) to Mesa's Form 10-K, dated
                            December 31, 1991).
         10.18           -- Omnibus Amendment to Collateral Instruments to
                            Supplemental Stipulation and Agreement, dated June 19,
                            1991, between Colorado Interstate Gas Company and Mesa
                            Operating Limited Partnership (incorporated by reference
                            to Exhibit 10(u) to Mesa's Form 10-K, dated December 31,
                            1991).
         10.19           -- Amarillo Supply Agreement between Mesa Operating Limited
                            Partnership, Seller, and Energas Company, a division of
                            Atmos Energy Corporation, Buyer, dated effective January
                            2, 1993 (incorporated by reference to Exhibit 10.14 to
                            Mesa's Form 10-K, dated December 31, 1995).
         10.20           -- Gas Supply Agreement, dated May 11, 1994, between MOC, as
                            successor to Mesa Operating Limited Partnership, acting
                            on behalf of itself and as agent for Hugoton Capital
                            Limited Partnership, and Williams Gas Marketing Company,
                            and Gas Supply Guarantee, dated May 11, 1994
                            (incorporated by reference to Exhibit 10.16 to Mesa's
                            Form 10-K, dated December 31, 1995).
         10.21           -- Gas Transportation Agreement, dated June 14, 1994,
                            between Western Resources, Inc. and MOC, acting on behalf
                            of itself and as agent for Hugoton Capital Limited
                            Partnership (incorporated by reference to Exhibit 10.24
                            to Mesa's Form 10-K, dated December 31, 1994).
         10.22           -- 1991 Stock Option Plan of Mesa (incorporated by reference
                            to Exhibit 10(v) to Mesa's Form 10-K, dated December 31,
                            1991).
         10.23           -- Interruptible Gas Transportation and Sales Agreement,
                            dated January 1, 1991, between Mesa Operating Limited
                            Partnership and Energas Company and Amendment, dated
                            January 1, 1995 (incorporated by reference to Exhibit
                            10.22 to Mesa's Form 10-K, dated December 31, 1995).
         10.24           -- "B" Contract Operating Agreement, dated January 1, 1988,
                            between Mesa Operating Limited Partnership and Colorado
                            Interstate Gas Company (incorporated by reference to
                            Exhibit 10.23 to Mesa's Form 10-K, dated December 31,
                            1995).
         10.25           -- Gathering Agreement, dated May 29, 1987, between Mesa
                            Operating Limited Partnership and Colorado Interstate Gas
                            Company (incorporated by reference to Exhibit 10.15 to
                            Pioneer's Quarterly Report on Form 10-Q for the period
                            ended September 30, 1997, File No. 001-13245).
         10.26           -- Amendment to Gathering Agreement, dated July 15, 1990,
                            between Colorado Interstate Gas Company and Mesa
                            Operating Limited Partnership (incorporated by reference
                            to Exhibit 10.24 to Mesa's Form 10-K, dated December 31,
                            1995).
         10.27           -- Amendment to 1990 Gathering Agreement Amendment, dated
                            September 1, 1997, between Colorado Interstate Gas
                            Company and Pioneer USA (incorporated by reference to
                            Exhibit 10.6 to Pioneer's Quarterly Report on Form 10-Q
                            for the period ended September 30, 1997, File No.
                            001-13245).
         10.28           -- Gas Purchase Agreement, dated January 1, 1996, between
                            MOC, as Seller, and KN Marketing L.P., as Buyer, and
                            Amendment, dated August 1, 1995 (incorporated by
                            reference to Exhibit 10.25 to Mesa's Form 10-K, dated
                            December 31, 1995).
         10.29           -- Employment Agreement, dated as of August 21, 1996,
                            between Mesa and I. Jon Brumley (incorporated by
                            reference to Exhibit 10.26 of Mesa's Form 10-K, dated
                            December 31, 1996).
</TABLE>
 
                                      II-5
<PAGE>   33
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.30           -- Stock Purchase Agreement, dated April 26, 1996, between
                            Mesa and DNR (incorporated by reference to Exhibit No. 10
                            to Mesa's Form 8-K filed on April 29, 1996).
         10.31           -- 1996 Incentive Plan of Mesa (incorporated by reference to
                            Exhibit 10.28 to Pioneer's Registration Statement on Form
                            S-4, dated June 27, 1997, Registration No. 333-26951).
         10.32           -- Mesa Management Severance Plan, dated April 4, 1997,
                            including a Schedule of Participants on Schedule A for
                            the purpose of defining the payment of certain benefits
                            upon the termination of the officer's employment under
                            certain circumstances (incorporated by reference to
                            Exhibit 10.29 to Pioneer's Registration Statement on Form
                            S-4, dated June 27, 1997, Registration No. 333-26951).
         10.33           -- Parker & Parsley Petroleum Company Long-Term Incentive
                            Plan, dated February 19, 1991, (incorporated by reference
                            to Exhibit 4.1 to Parker & Parsley's Registration
                            Statement on Form S-8, Registration No. 33-38971).
         10.34           -- First Amendment to the Parker & Parsley Petroleum Company
                            Long-Term Incentive Plan, dated August 23, 1991
                            (incorporated by reference to Exhibit 10.2 to Parker &
                            Parsley's Registration Statement on Form S-1, dated
                            February 28, 1992, Registration No. 33-46082).
         10.35           -- Agreement of Partnership of P&P Employees 89-B Conv.,
                            L.P. (formerly P&P Employees 89-B GP), dated October 31,
                            1989, among Parker & Parsley, Ltd. and the Investor
                            Partners (as defined therein, which includes individuals
                            who are directors and executive officers of Parker &
                            Parsley), together with a schedule identifying
                            substantially identical documents and setting forth the
                            material details in which those documents differ from the
                            foregoing document (incorporated by reference to Exhibit
                            10.50 to Parker & Parsley's Registration Statement on
                            Form S-4, dated December 31, 1990, Registration No.
                            33-38436).
         10.36           -- Amendment to Agreement of Partnership of P&P Employees
                            89-B GP, dated May 31, 1990, among Parker & Parsley, Ltd.
                            and the Investor Partners (as defined therein, which
                            includes individuals who are directors and executives
                            officers of Parker & Parsley), together with a schedule
                            identifying substantially identical documents and setting
                            forth the material details in which those documents
                            differ form the foregoing document (incorporated by
                            reference to Exhibit 10.51 to Parker & Parsley's
                            Registration Statement on Form S-4, dated December 31,
                            1990, Registration No. 33-38436).
         10.37           -- Schedule identifying additional documents substantially
                            identical to the Amendment to Agreement of Partnership of
                            P&P Employees 89-B GP included as Exhibit 10.5 and
                            setting forth the material details in which those
                            documents differ from that document (incorporated by
                            reference to Exhibit 10.52 to Parker & Parsley's
                            Registration Statement on Form S-1, dated February 28,
                            1992, Registration No. 33-46082).
         10.38           -- Agreement of Partnership of P&P Employees 90 Spraberry
                            Private Development GP, dated October 16, 1990, among
                            Parker & Parsley, Ltd., James D. Moring, and the General
                            Partners (as defined therein, which includes individuals
                            who are directors and executive officers of Parker &
                            Parsley), and form of Amendment to Agreement of
                            Partnership of P&P Employees 90 Spraberry Private
                            Development GP, together with a schedule identifying
                            substantially identical documents and setting forth the
                            material details in which those documents differ from the
                            foregoing document (incorporated by reference to Exhibit
                            10.52 to Parker & Parsley's Registration Statement on
                            Form S-4, dated December 31, 1990, Registration No.
                            33-38436).
</TABLE>
 
                                      II-6
<PAGE>   34
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.39           -- Amendment to Agreement of Partnership of Parker & Parsley
                            90-A GP, dated February 19, 1991, among Parker & Parsley
                            Development Company and the Investor Partners (as defined
                            therein, which includes individuals who are directors and
                            executive officers of Parker & Parsley), together with a
                            schedule identifying substantially identical documents
                            and setting forth the material details in which those
                            documents differ from the foregoing document
                            (incorporated by reference to Exhibit 10.58 to Parker &
                            Parsley's Registration Statement on Form S-1, dated
                            February 28, 1992, Registration No. 33-46082).
         10.40           -- Agreement of Partnership of P&P Employees 91-A, GP, dated
                            September 30, 1991, among Parker & Parsley Development
                            Company, James D. Moring, and the General Partners (as
                            defined therein, which includes individuals who are
                            directors and executive officers of Parker & Parsley),
                            together with a schedule identifying substantially
                            identical documents and setting forth the material
                            details in which those documents differ from the
                            foregoing document (incorporated by reference to Exhibit
                            10.61 to Parker & Parsley's Registration Statement on
                            Form S-1, dated February 28, 1992, Registration No.
                            33-46082).
         10.41           -- Development Drilling Program Agreement of Parker &
                            Parsley 91-A Development Drilling Program, dated
                            September 30, 1991, among Parker & Parsley Development
                            Company, the P&P Employee Participants (as defined
                            therein, which includes individuals who are directors and
                            executive officers of Parker & Parsley), P&P Employees
                            91-A, GP, and Parker & Parsley 91-A, L.P., together with
                            a schedule identifying substantially identical documents
                            and setting forth the material details in which those
                            documents differ from the foregoing document
                            (incorporated by reference to Exhibit 10.63 to Parker &
                            Parsley's Registration Statement on Form S-1, dated
                            February 28, 1992, Registration No. 33-46082).
         10.42           -- Development Drilling Program Agreement, dated August 1,
                            1989, among Parker & Parsley, Ltd., Parker & Parsley
                            Development Partners L.P., certain key employees of
                            Parker & Parsley, Ltd. (which includes individuals who
                            are directors and executive officers of Parker &
                            Parsley), and related persons, P&P Employees 89-A GP, and
                            Parker & Parsley 89- A, GP, and Parker & Parsley 89-A,
                            L.P., together with a schedule identifying substantially
                            identical documents and setting forth the material
                            details in which those documents differ from the
                            foregoing document (incorporated by reference to Exhibit
                            10.56 to Parker & Parsley's Registration Statement on
                            Form S-4, dated December 31, 1990, Registration No.
                            33-38436).
         10.43           -- Amendment to Development Drilling Program Agreement,
                            dated February 19, 1991, amending the Development
                            Drilling Program Agreement included in Exhibit 10.11,
                            together with a schedule identifying substantially
                            identical documents and setting forth the material
                            details in which those documents differ from the
                            foregoing document (incorporated by reference to Exhibit
                            10.66 to Parker & Parsley's Registration Statement on
                            Form S-1, dated February 28, 1992, Registration No.
                            33-46082).
         10.44           -- Amendment to Agreement of Partnership of P&P Employees 90
                            Spraberry Private Development GP, dated April 22, 1991,
                            among the Partners (as defined therein, which includes
                            individuals who are directors and executive officers of
                            Parker & Parsley) (incorporated by reference to Exhibit
                            10.67 to Parker & Parsley's Registration Statement on
                            Form S-1, dated February 28, 1992, Registration No.
                            33-46082).
</TABLE>
 
                                      II-7
<PAGE>   35
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.45           -- Agreement of Limited Partnership of Parker & Parsley 1992
                            Direct Investment Program, Ltd., dated as of July 24,
                            1992, among Parker & Parsley Development Company, as
                            managing general partner, and certain key employees of
                            Parker & Parsley (including individuals who are directors
                            and executive officers of Parker & Parsley), as
                            non-managing general partners and limited partners
                            (incorporated by reference to Exhibit 10.57 to Parker
                            Parsley's Annual Report on Form 10-K for the year ended
                            December 31, 1993, Commission File No. 1-10695).
         10.46           -- Agreement of Limited Partnership of Parker & Parsley 1993
                            Direct Investment Program, Ltd., dated as of January 1,
                            1993, among Parker & Parsley Development Company, as
                            managing general partner, and certain key employees of
                            Parker & Parsley (including individuals who are directors
                            and executive officers of Parker & Parsley), as
                            non-managing general partners and limited partners
                            (incorporated by reference to Exhibit 10.49 to Parker &
                            Parsley's Annual Report on Form 10-K for the year ended
                            December 31, 1993, Commission File No. 1-10695).
         10.47           -- Agreement of Limited Partnership of Parker & Parsley 1994
                            Direct Investment Program, Ltd., dated as of January 1,
                            1994, among Parker & Parsley Development Company, as
                            managing general partner, and certain key employees of
                            Parker & Parsley (including individuals who are directors
                            and executive officers of Parker & Parsley), as
                            non-managing general partners and limited partners
                            (incorporated by reference to Exhibit 10.20 to Parker &
                            Parsley's Annual Report on Form 10-K for the year ended
                            December 31, 1994, Commission File No. 1-10695).
         10.48           -- Stock Acquisition Loan Agreement entered into as of June
                            15, 1995, between Parker & Parsley and Scott D.
                            Sheffield, together with Schedule I identifying executive
                            officers with substantially identical agreements
                            providing for Parker & Parsley's loans to such officers
                            in order to acquire shares of Parker & Parsley's Common
                            Stock, par value $0.01 per share (incorporated by
                            reference to Exhibit 10.48 to Pioneer's Registration
                            Statement on Form S-3, Registration No. 333-39381).
         10.49           -- Omnibus Amendment to Nonstatutory Stock Option
                            Agreements, included as part of the Long-Term Incentive
                            Plan, dated as of November 16, 1995, between Parker &
                            Parsley and Named Executive Officers identified on
                            Schedule 1 setting forth additional details relating to
                            the Long-Term Incentive Plan (incorporated by reference
                            to Parker & Parsley's Annual Report on Form 10-K for the
                            year ended December 31, 1995, Commission File No.
                            1-10695).
         10.50           -- Severance Agreement, dated as of August 8, 1997, between
                            Pioneer and Scott D. Sheffield, together with a schedule
                            identifying substantially identical agreements between
                            Pioneer and each of the other named executive officers
                            identified on Schedule I for the purpose of defining the
                            payment of certain benefits upon the termination of the
                            officer's employment under certain circumstances
                            (incorporated by reference to Exhibit 10.7 to Pioneer's
                            Quarterly Report on Form 10-Q for the period ended
                            September 30, 1997, File No. 001-13245).
         10.51           -- Indemnification Agreement, dated as of August 8, 1997,
                            between Pioneer and Scott D. Sheffield, together with a
                            schedule identifying substantially identical agreements
                            between Pioneer and each of Pioneer's other directors and
                            named executive officers identified on Schedule I
                            (incorporated by reference to Exhibit 10.8 to Pioneer's
                            Quarterly Report on Form 10-Q for the period ended
                            September 30, 1997, File No. 001-13245).
         10.52           -- Pioneer Natural Resources Company Long-Term Incentive
                            Plan (incorporated by reference to Exhibit 4.1 to
                            Pioneer's Registration Statement on Form S-8,
                            Registration No. 333-35087).
</TABLE>
 
                                      II-8
<PAGE>   36
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
         10.53           -- Pioneer Natural Resources Company Employee Stock Purchase
                            Plan (incorporated by reference to Exhibit 4.1 to
                            Pioneer's Registration Statement on Form S-8,
                            Registration No. 333-35165).
         10.54           -- Pioneer Natural Resources Company Deferred Compensation
                            Retirement Plan (incorporated by reference to Exhibit 4.1
                            to Pioneer's Registration Statement on Form S-8,
                            Registration No. 333-39153).
         10.55           -- Pioneer Natural Resources USA, Inc. 401(k) Plan
                            (incorporated by reference to Exhibit 4.1 to Pioneer's
                            Registration Statement on Form S-8, Registration No.
                            333-39249).
         10.56           -- Credit Facility Agreement (Primary Facility), dated as of
                            August 7, 1997, between Pioneer USA, as Borrower, and
                            NationsBank of Texas, N.A., as Administrative Agent, CIBC
                            Inc., as Documentation Agent, Morgan Guaranty Trust
                            Company of New York, as Documentation Agent, and The
                            Chase Manhattan Bank, as Syndication Agent; Bank of
                            America Natural Trust and Savings Association, The Bank
                            of New York, The Bank of Nova Scotia, Royal Bank of
                            Canada, Union Bank of California, N.A., The Fuji Bank,
                            Limited-Houston Agency and Wells Fargo Bank, N.A., as
                            Co-Agents; and certain other lenders (incorporated by
                            reference to Exhibit 10.1 to Pioneer's Form 8-K, dated
                            August 7, 1997, File No. 333-26951).
         10.57           -- Credit Facility Agreement (364 Day Facility), dated as of
                            August 7, 1997, between Pioneer USA, as Borrower, and
                            NationsBank of Texas, N.A., as Administrative Agent, CIBC
                            Inc., as Documentation Agent, Morgan Guaranty Trust
                            Company of New York, as Documentation Agent, and The
                            Chase Manhattan Bank, as Syndication Agent; Bank of
                            America Natural Trust and Savings Association, The Bank
                            of New York, The Bank of Nova Scotia, Royal Bank of
                            Canada, Union Bank of California, N.A., The Fuji Bank,
                            Limited-Houston Agency and Wells Fargo Bank, N.A., as
                            Co-Agents; and certain other lenders (incorporated by
                            reference to Exhibit 10.2 to Pioneer's Form 8-K, dated
                            August 7, 1997, File No. 333-26951).
         10.58*          -- Form of Share Purchase Agreement between Pioneer Natural
                            Resources (Canada) Ltd., Trimac Corporation and 761795
                            Alberta Ltd.
         10.59*          -- Form of Share Purchase Agreement between Pioneer Natural
                            Resources (Canada) Ltd., Guy Turcotte and 398215 Alberta
                            Ltd.
         23.1*           -- Consent of KPMG Peat Marwick LLP.
         23.2*           -- Consent of Arthur Andersen LLP.
         23.3*           -- Consent of Price Waterhouse, chartered accountants.
         23.4*           -- Consent of Coopers & Lybrand L.L.P.
         23.5*           -- Consent of Netherland, Sewell & Associates, Inc.
         23.6*           -- Consent of Williamson Petroleum Consultants, Inc.
         23.7*           -- Consent of Miller and Lents, Ltd.
         23.8*           -- Consent of Gilbert Lausten Jung Associates, Ltd.
         23.9*           -- Consent of Martin Petroleum and Associates.
         23.10*          -- Consent of Vinson & Elkins L.L.P. (included in the
                            opinion filed as Exhibit 5.1 to this Registration
                            Statement).
         23.11*          -- Consent of MacKimmie Matthews (included in the opinion
                            filed as Exhibit 8.1 to this Registration Statement).
         23.12*          -- Consent of Vinson & Elkins L.L.P. (included in the
                            opinion filed as Exhibit 8.2 to this Registration
                            Statement).
         24.1*           -- Powers of Attorney of directors and officers of Pioneer.
</TABLE>
 
- ---------------
 
* Filed herewith.
 
                                      II-9
<PAGE>   37
 
ITEM 17. UNDERTAKINGS
 
     The undersigned Registrant hereby undertakes:
 
          (a) To file, during any period in which offers or sales are being
     made, a post-effective amendment to this Registration Statement.
 
             (1) To include any prospectus required by Section 10(a)(3) of the
        Securities Act of 1933 (the "Securities Act");
 
             (2) To reflect in the prospectus any facts or events arising after
        the effective date of this Registration Statement (or the most recent
        post-effective amendment thereof) which, individually or in the
        aggregate, represent a fundamental change in the information set forth
        in this Registration Statement; and
 
             (3) To include any material information with respect to the plan of
        distribution not previously disclosed in this Registration Statement or
        any material change to the information in this Registration Statement;
 
             Provided, however, that clauses (1) and (2) above do not apply if
        the information required to be included in a post-effective amendment by
        those clauses is contained in periodic reports filed by the Registrant
        pursuant to Section 13 or Section 15(d) of the Exchange Act that are
        incorporated by reference into this Registration Statement;
 
          (b) That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new registration statement relating to the securities offered therein, and
     the offering of the securities at that time shall be deemed to be the
     initial bona fide offering thereof; and
 
          (c) To remove from registration by means of a post-effective amendment
     any of the securities being registered that remain unsold at the
     termination of the offering.
 
     The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act that is incorporated by reference in this Registration Statement shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of the securities at that time shall be deemed to be
the initial bona fide offering thereof.
 
     Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to directors, officers, and controlling persons of the
Registrant pursuant to the provisions described in Item 15 above or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Securities Act and is, therefore, unenforceable. In the event that a
claim for indemnification against such liabilities (other than the payment by
the Registrant of expenses incurred or paid by a director, officer, or
controlling person of the Registrant in the successful defense of any action,
suit, or proceeding) is asserted by the director, officer, or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a court of appropriate jurisdiction the question whether
such indemnification by it is against public policy as expressed in the
Securities Act and will be governed by the final adjudication of the issue.
 
     For purposes of determining any liability under the Securities Act of 1933,
the information omitted from the form of prospectus filed as part of this
registration statement in reliance upon Rule 430A and contained in a form of
prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h)
under the Securities Act shall be deemed to be part of this Registration
Statement as of the time it was declared effective.
 
     For the purpose of determining any liability under the Securities Act of
1933, each post-effective amendment that contains a form of prospectus shall be
deemed to be a new registration statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.
                                      II-10
<PAGE>   38
 
                                   SIGNATURES
 
     Pursuant to the requirements of the Securities Act of 1933, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in Irving, Texas, on February 12, 1998.
 
                                          PIONEER NATURAL RESOURCES COMPANY
 
                                          By:    /s/ SCOTT D. SHEFFIELD
                                            ------------------------------------
                                                    Scott D. Sheffield,
                                               President and Chief Executive
                                                           Officer
 
     Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated. Each person whose signature appears below hereby authorizes and
appoints Scott D. Sheffield, Mark L. Withrow and M. Garrett Smith, or any of
them, as his attorney-in-fact to sign on his behalf individually and in the
capacity stated below all amendments and post-effective amendments to this
Registration Statement (including any additional registration statement filed
pursuant to Rule 462 of the Securities Act with respect to this Registration
Statement) as that attorney-in-fact may deem necessary or appropriate.
 
<TABLE>
<CAPTION>
                      SIGNATURE                                    TITLE                    DATE
                      ---------                                    -----                    ----
<C>                                                    <S>                            <C>
                 /s/ I. JON BRUMLEY                    Chairman of the Board and      February 12, 1998
- -----------------------------------------------------    Director
                   I. Jon Brumley
 
               /s/ SCOTT D. SHEFFIELD                  Director, President and Chief  February 12, 1998
- -----------------------------------------------------    Executive Officer
                 Scott D. Sheffield                      (principal executive
                                                         officer)
 
                /s/ M. GARRETT SMITH                   Executive Vice President and   February 12, 1998
- -----------------------------------------------------    Chief Financial Officer
                  M. Garrett Smith                       (principal financial and
                                                         accounting officer)
 
                                                       Director                       February   , 1998
- -----------------------------------------------------
                  James R. Baroffio
 
               /s/ R. HARTWELL GARDNER                 Director                       February 12, 1998
- -----------------------------------------------------
                 R. Hartwell Gardner
 
               /s/ JOHN S. HERRINGTON                  Director                       February 12, 1998
- -----------------------------------------------------
                 John S. Herrington
 
                /s/ KENNETH A. HERSH                   Director                       February 12, 1998
- -----------------------------------------------------
                  Kenneth A. Hersh
 
                                                       Director                       February   , 1998
- -----------------------------------------------------
                  James L. Houghton
 
                 /s/ JERRY P. JONES                    Director                       February 12, 1998
- -----------------------------------------------------
                   Jerry P. Jones
 
                                                       Director                       February   , 1998
- -----------------------------------------------------
                  T. Boone Pickens
</TABLE>
 
                                      II-11
<PAGE>   39
 
<TABLE>
<CAPTION>
                      SIGNATURE                                        TITLE                          DATE
- ------------------------------------------------------  ------------------------------------  --------------------
<C>                                                     <S>                                   <C>
/s/ RICHARD E. RAINWATER                                Director                                 February 12, 1998
By: KENNETH A. HERSH, ATTORNEY-IN-FACT
- ----------------------------------------------------
    Richard E. Rainwater
        by Kenneth A. Hersh, Attorney-in-fact
 
              /s/ CHARLES E. RAMSEY, JR.                Director                                 February 12, 1998
- ------------------------------------------------------
                Charles E. Ramsey, Jr.
 
                 /s/ ARTHUR L. SMITH                    Director                                 February 13, 1998
- ------------------------------------------------------
                   Arthur L. Smith
 
                                                        Director                                 February   , 1998
- ------------------------------------------------------
                   Philip B. Smith
 
               /s/ ROBERT L. STILLWELL                  Director                                 February 12, 1998
- ------------------------------------------------------
                 Robert L. Stillwell
 
                /s/ MICHAEL D. WORTLEY                  Director                                 February 12, 1998
- ------------------------------------------------------
                  Michael D. Wortley
</TABLE>
 
                                      II-12
<PAGE>   40
 
                               INDEX TO EXHIBITS
 
<TABLE>
<CAPTION>
        EXHIBIT
         NUMBER                                  DESCRIPTION
        -------                                  -----------
<C>                      <S>
          5.1            -- Opinion of Vinson & Elkins L.L.P. as to the legality of
                            the securities to be registered.
          8.1            -- Opinion of MacKimmie Matthews regarding tax matters.
          8.2            -- Opinion of Vinson & Elkins L.L.P. regarding tax matters.
         10.58           -- Form of Share Purchase Agreement between Pioneer Natural
                            Resources (Canada) Ltd., Trimac Corporation and 761795
                            Alberta Ltd.
         10.59           -- Form of Share Purchase Agreement between Pioneer Natural
                            Resources (Canada) Ltd., Buy Turcotte and        .
         23.1            -- Consent of KPMG Peat Marwick LLP.
         23.2            -- Consent of Arthur Andersen LLP.
         23.3            -- Consent of Price Waterhouse, chartered accountants.
         23.4            -- Consent of Coopers & Lybrand L.L.P.
         23.5            -- Consent of Netherland, Sewell & Associates, Inc.
         23.6            -- Consent of Williamson Petroleum Consultants, Inc.
         23.7            -- Consent of Miller and Lents, Ltd.
         23.8            -- Consent of Gilbert Lausten Jung Associates, Ltd.
         23.9            -- Consent of Martin Petroleum and Associates.
</TABLE>

<PAGE>   1
                                                                    EXHIBIT 5.1




                      [VINSON & ELKINS L.L.P. LETTERHEAD]




                                February 13, 1998




Pioneer Natural Resources Company
1400 Williams Square West
5205 North O'Connor Blvd.
Irving, Texas  75039

Ladies and Gentlemen:

         We have acted as counsel for Pioneer Natural Resources Company, a
Delaware corporation (the "Company"), in connection with the Company's
registration under the Securities Act of 1933 (the "Act") of the offer and
issuance of 10,901,924 shares of common stock, par value $.01 per share (the
"Pioneer Common Stock"), of the Company pursuant to the Company's Registration
Statement on Form S-3 filed with the Securities and Exchange Commission (the
"Commission") on February 13, 1998 (the "Registration Statement").

         In reaching the opinions set forth herein, we have examined and are
familiar with the originals or copies, certified or otherwise, of such
documents and records of the Company and such statutes, regulations, and other
instructions as we have deemed necessary or advisable for purposes of this
opinion, including (i) the Registration Statement, (ii) the Amended and
Restated Certificate of Incorporation of the Company, and (iii) the Amended and
Restated By-Laws of the Company.

         We have assumed that (i) all information contained in all documents
reviewed by us is true, correct, and complete, (ii) all signatures on all
documents reviewed by us are genuine, (iii) all documents submitted to us as
originals are true and complete, (iv) all documents submitted to us as copies
are true and complete copies of the originals thereof, and (v) all persons
executing and delivering originals or copies of documents examined by us were
competent to execute and deliver such documents. In addition, we have assumed
that: (i) the shares of Pioneer Common Stock that have yet to be issued will be
issued in accordance with the Combination Agreement in the form previously
reviewed by us (the "Combination Agreement"), (ii) the full consideration for
each share of Pioneer Common Stock that has yet to be issued shall be received
by the Company and in no event shall be less than the par value of such share
of Pioneer Common Stock, and (iii) certificates evidencing the shares of
Pioneer Common Stock that have yet to be issued shall be properly executed and
delivered by the Company in accordance with the Delaware General Corporation
Law ("DGCL").



<PAGE>   2


Pioneer Natural Resources Company
February 13, 1998
Page 2

         Based on the foregoing and having due regard for the legal
considerations we deem relevant, we are of the opinion that the shares of
Pioneer Common Stock, when issued in accordance with the Combination Agreement,
will be validly issued by the Company, fully paid, and non-assessable.

         This opinion is limited in all respects to the DGCL and the federal
laws of the United States of America. You should be aware that we are not
admitted to the practice of law in the State of Delaware.

         This opinion letter may be filed as an exhibit to the Registration
Statement. Consent is also given to the reference to us under the caption
"Legal Matters" in the Registration Statement and in the Prospectus included in
the Registration Statement as having passed on the validly of the shares of
Pioneer Common Stock. In giving this consent, however, we do not thereby admit
that we fall within the category of persons whose consent is required under
Section 7 of the Act or the rules and regulations of the Commission promulgated
thereunder.

                                           Very truly yours,

                                           /s/  VINSON & ELKINS L.L.P.



<PAGE>   1
                                                                    EXHIBIT 8.1




                       [MacKIMMIE MATTHEWS LETTERHEAD]


                                                               February 13, 1998





Pioneer Natural Resources Company
1400 Williams Square West
5205 North O'Connor Blvd.
Irving, Texas  75039

                       REGISTRATION STATEMENT ON FORM S-3

We have acted as counsel to Pioneer Natural Resources Company, a Delaware
corporation ("Pioneer"), and Pioneer Natural Resources (Canada) Ltd., a British
Columbia corporation ("Pioneer Canada"), in connection with the offer of
10,901,924 shares of Pioneer Common Stock issuable upon the redemption by
Pioneer Canada or the acquisition by Pioneer of Exchangeable Shares, pursuant
to a Registration Statement on Form S-3, (the "Registration Statement") filed
with the Securities and Exchange Commission under the United States Securities
Act of 1933 on February 13, 1998. In connection therewith, we have participated
in the preparation of the discussion set forth under the subcaption "Income Tax
Considerations -- Canadian Federal Income Tax Considerations" (the
"Discussion") in the Registration Statement. Capitalized terms used and not
otherwise defined herein are used as defined in the Registration Statement.

The Discussion, subject to the qualifications stated therein, reflects our
opinion as to the material Canadian federal income tax considerations for a
Pioneer Canada Shareholder in regard to the ownership of Pioneer Canada
Exchangeable Shares and the receipt of shares of Pioneer Common Stock upon the
redemption of a Pioneer Canada Shareholder's Exchangeable Shares by Pioneer
Canada or the acquisition by Pioneer of such Exchangeable Shares.

We hereby consent to the use of our name in the Registration Statement and to
the filing of this opinion as an exhibit to the Registration Statement. However,
this consent does not constitute an admission that we are "experts" within the
meaning of such term as used in the Securities Act of 1933.




                                                MacKIMMIE MATTHEWS 

                                                /s/ MacKIMMIE MATTHEWS


<PAGE>   1
                                                                    EXHIBIT 8.2




                      [VINSON & ELKINS L.L.P. LETTERHEAD]



(214) 220-7700                                                    (214) 220-7716

                              February 13, 1998



Pioneer Natural Resources Company
1400 Williams Square West
5205 North O'Connor Blvd.
Irving, Texas  75039

         Re:  Registration Statement on Form S-3

Ladies and Gentlemen:

         We have acted as counsel to Pioneer Natural Resources Company, a
Delaware corporation, in connection with the offer of 10,901,924 shares of
Pioneer Common Stock issuable upon the redemption by Pioneer Canada or the
acquisition by Pioneer of Exchangeable Shares, pursuant to a Registration
Statement on Form S-3, (the "Registration Statement")  filed with the
Securities and Exchange Commission under the Securities Act of 1933 on February
13, 1998. In connection therewith, we have participated in the preparation of
the discussion set forth under the subcaption "Income Tax Considerations --
United States Federal Income Tax Considerations" (the "Discussion") in the
Registration Statement. Capitalized terms used and not otherwise defined herein
are used as defined in the Registration Statement.

         The Discussion, subject to the qualifications stated therein, reflects
our opinion as to the material United States federal income tax considerations
for a Pioneer Canada Shareholder in regard to the ownership of Pioneer Canada
Exchangeable Shares and the receipt of shares of Pioneer Common Stock upon the
redemption of a Pioneer Canada Shareholder's Exchangeable Shares by Pioneer
Canada or the acquisition by Pioneer of such Exchangeable Shares.

         We hereby consent to the use of our name in the Registration Statement
and to the filing of this opinion as an exhibit to the Registration Statement.
However, this consent does not constitute an admission that we are "experts"
within the meaning of such term as used in the Securities Act of 1933.

                                                Respectfully submitted,



                                                /s/  VINSON & ELKINS L.L.P.




<PAGE>   1
                                                                   EXHIBIT 10.58

                            SHARE PURCHASE AGREEMENT
                               February 13, 1998
BETWEEN

                 PIONEER NATURAL RESOURCES (CANADA) LTD., a body corporate
                 continued under the laws of Alberta ("PURCHASER")

                                      AND

                 TRIMAC CORPORATION, a body corporate incorporated under the
                 laws of the Province of Alberta ("TRIMAC")

                                      AND

                 761795 ALBERTA LTD., a body corporate incorporated under the
                 laws of the Province of Alberta ("SUBSIDIARY")
RECITALS

A.       The Subsidiary is a wholly owned subsidiary of Trimac;

B.       Trimac is the legal and beneficial holder of all outstanding Class A
         Shares of 761582 Alberta Ltd. ("Newco"), and Subsidiary is the legal
         and beneficial holder of all outstanding Class D Preferred Shares,
         Series 1 of Newco, such shares collectively being the only outstanding
         shares of any class in the capital of Newco;

C.       The Purchaser desires to purchase and the Vendors desire to sell the
         Newco Shares on the terms set out in this Agreement;

D.       The only asset of Newco is a total of 3,113,624 Exchangeable Shares in
         the capital of the Purchaser.

THE PARTIES AGREE AS FOLLOWS.
<PAGE>   2
                                   ARTICLE 1
                                 INTERPRETATION

1.1      In this Agreement, including the premises hereto and this section,
         unless the context otherwise requires, the following terms shall have
         the following respective meanings:

         "AGREEMENT" means this Agreement and any schedules attached hereto and
         any amendments hereof;

         "ARRANGEMENT SHARES" means the 3,113,624 Exchangeable Shares held by
         Newco;

         "CLOSING" means the completion of the transactions contemplated by the
         Agreement;

         "CLOSING DATE" means February 13, 1998 or such other date as the
         parties hereto may agree;

         "CLOSING TIME" means 2:00 p.m., Calgary Time, or such other time as
         the parties hereto may agree, on the Closing Date;

         "NEW EXCHANGEABLE SHARES" means the Exchangeable Shares to be issued
         to the Vendors pursuant to this Agreement;

         "NEWCO" means 761582 Alberta Ltd., an Alberta corporation;

         "NEWCO CLASS A SHARES" means 5,000,000 outstanding Class A Shares of
         Newco;

         "NEWCO PREFERRED SHARES" means 22,000 Class D Preferred Shares Series
         1 of Newco;

         "NEWCO SHARES" means the Newco Class A Shares and the Newco Preferred
         Shares;

         "PURCHASER TAX COST" means any liability for any Tax which (i) is
         suffered or incurred, directly or indirectly, by Purchaser, and (ii)
         would not have been so suffered or incurred had the transactions
         contemplated by this Agreement not taken place or had the Arrangement
         Shares not been cancelled in connection with the winding up or
         dissolution of Newco. For purposes of the foregoing, a Tax shall be
         considered to be suffered or incurred by Purchaser indirectly if such
         Tax is suffered or incurred by any
<PAGE>   3
                                     - 3 -


         person related to Purchaser within the meaning of Section 954(d)(3) of
         the United States Internal Revenue Code of 1986, as amended, assuming
         for such purpose that Purchaser is a "controlled foreign corporation"
         within the meaning of Section 957 of said Code.

         "TAX" means (i) any Canadian domestic, United States or other foreign
         net income, alternative or add-on minimum, gross income, gross
         receipts, sales, use, ad valorem, value added, transfer, franchise,
         profits, license, withholding, payroll, employment, excise,
         production, severance, stamp, occupation, premium, property,
         environment, or windfall profit tax, custom, duty or other tax,
         governmental fee or other like assessment or charge of any kind
         whatsoever, together with any interest and/or any penalty, addition to
         tax or additional amount imposed by any taxing authority, and (ii) any
         liability of a person for the payment of any amounts of the type
         described in clause (i) as a result of being a member of an affiliated
         or consolidated group or arrangement whereby liability of such person
         for the payment of such amounts was determined or taken into account
         with reference to the liability of any other person for any period.

         "VENDORS" means collectively, Trimac and Subsidiary.

1.2      Headings of the articles or sections hereof are inserted for
         convenience of reference only and shall not affect the construction or
         interpretation of this Agreement.

1.3      In this Agreement, words importing the singular number only shall
         include the plural and vice versa, and words importing the masculine
         gender shall include the feminine and neuter gender, and words
         importing persons shall include provincial or federal companies,
         corporations, partnerships, syndicates, trusts and any number or
         aggregate of persons, all as the context may require.

1.4      All dollar amounts in this Agreement are expressed in Canadian
         dollars.

1.5      This Agreement and all amendments, modifications, alterations or
         supplements thereto shall, in all respects, be subject to and
         interpreted, construed and enforced in accordance with the laws of the
         Province of Alberta. Each party hereto submits to and accepts the
         jurisdiction of the Courts of the Province of Alberta for all purposes
         hereof.
<PAGE>   4
                                     - 4 -


                                   ARTICLE 2
                                 SALE OF SHARES

2.1      Subject to the terms and conditions of this Agreement, the Vendors
         agree to sell, assign, transfer and convey to the Purchaser and the
         Purchaser agrees to purchase from the Vendors, on the Closing Date,
         the Newco Shares.

                                   ARTICLE 3
                                 PURCHASE PRICE

3.1      In consideration for the Newco Shares, the Purchaser shall issue to
         the Vendors an aggregate of 3,113,624 New Exchangeable Shares. The 
         purchase consideration shall be allocated between the Vendors as 
         follows:

                 Trimac       2,431,774   New Exchangeable Shares
                 Subsidiary     681,850   New Exchangeable Shares

                                   ARTICLE 4
               VENDOR'S REPRESENTATIONS, WARRANTIES AND COVENANTS

4.1      Each of the Vendors jointly and severally represents and warrants to
         the Purchaser as follows effective on the date hereof and at the
         Closing Date:

         (a)     Newco is a corporation duly incorporated and subsisting under
                 the laws of the Province of Alberta and has all requisite
                 corporate power and authority to own the Arrangement Shares.

         (b)     The authorized and issued share capital of Newco consists of:

                   (i)    an unlimited number of Class A Shares of which
                          5,000,000 are issued and outstanding as fully paid
                          and non-assessable shares; and

                  (ii)    an unlimited number of Class B Shares, none of which
                          have been issued;

                 (iii)    an unlimited number of Class C Preferred Shares none
                          of which have been issued;

                  (iv)    an unlimited number of Class D Preferred Shares
                          issuable in series, of which 22,000 shares of the
                          first series, designated
<PAGE>   5
                                     - 5 -


                          Class D Preferred Shares Series 1, are issued and
                          outstanding as fully-paid and non-assessable.

         (c)     Trimac is the holder of record and the beneficial owner of the
                 Newco Class A Shares and the Subsidiary is the holder of
                 record and beneficial owner of the Newco Preferred Shares,
                 which collectively represent all of the issued and outstanding
                 shares in the capital of Newco and the Vendors are and on the
                 Closing Date will be the owner of all such Newco Shares with
                 good and marketable title thereto free and clear of any
                 option, security interest, lien, charge, encumbrance,
                 hypothecation, claim or right of others (other than the rights
                 of the Purchaser hereunder).

         (d)     Trimac is and at the Closing will be, the holder of record and
                 beneficial owner of all outstanding shares of the Subsidiary.

         (e)     Each of the Vendors has the legal right, power and authority
                 to sell, assign and transfer the Newco Shares being sold by it
                 hereunder free and clear of any option, security interest,
                 lien, charge, encumbrance, hypothecation, claim or right of
                 others (other than the rights of the Purchaser hereunder).

         (f)     There are no outstanding agreements, options, warrants, rights
                 of conversion or other rights pursuant to which Newco is or
                 may become obligated to issue any shares, or securities
                 convertible or exchangeable into shares, and there are no
                 outstanding obligations, understandings or commitments of
                 Newco to repurchase, redeem or otherwise acquire any
                 outstanding shares of its capital or restricting its ability
                 to issue shares.

         (g)     Newco is the beneficial owner of the Arrangement Shares, free
                 and clear of any option, security interest, lien, charge,
                 encumbrance, claim or right of others.

         (h)     Effective on the Closing Date, Newco will have no liabilities,
                 (whether actual, accrued, potential, contingent or otherwise).

         (i)     From the date of its incorporation until the Closing Date
                 Newco has not carried on any business or owned any assets,
                 other than cash and shares of Chauvco Resources Ltd. and the
                 Arrangement Shares and other securities received in the
                 arrangement of Chauvco Resources Ltd. which was effected
                 December 18, 1997.
<PAGE>   6
                                     - 6 -


         (j)     The corporate records and minute books of Newco are complete
                 and accurate in all material aspects.

         (k)     Each of the Vendors is a corporation validly subsisting under
                 the laws of the Province of Alberta, with the requisite
                 corporate power and authority to enter into and perform all of
                 its obligations under this Agreement and the execution,
                 delivery and performance of this Agreement and the
                 transactions contemplated hereby have been duly and validly
                 authorized by all requisite corporate action on the part of
                 each of the Vendors.

         (l)     The entering into of this Agreement by the Vendors and the
                 completion of the transactions contemplated hereby will not
                 result in the violation of any of the terms and provisions of
                 the constating documents or by-laws of any of the Vendors or
                 Newco or of any indenture or other agreement to which the
                 Vendors or Newco is a party.

         (m)     The entering into this Agreement by the Vendors and the
                 completion of the transactions contemplated hereby will not
                 result in the violation of any law or regulation of Canada or
                 of the Province of Alberta.

         (n)     This Agreement has been duly executed and delivered by the
                 Vendors and is a valid and binding obligation of each of the
                 Vendors enforceable against them in accordance with its terms.

         (o)     There is no action, suit, litigation, arbitration proceeding
                 or governmental proceeding including appeals and applications
                 for review, in which Newco is a party, either as plaintiff,
                 defendant, applicant, respondent or any other capacity
                 whatsoever. There are no outstanding orders of any court,
                 governmental agency or instrumentality, to which Newco, Trimac
                 or the Subsidiary is subject affecting, in any material
                 respect, the business, prospects, properties or condition
                 (financial or otherwise) of Newco or the ability of the
                 Vendors to consummate the transactions contemplated hereby.

         (p)     Each of the Vendors is not a non-resident of Canada within the
                 meaning of the Income Tax Act (Canada).  None of the Vendors
                 is a corporation incorporated under the laws of the United
                 States.

         (q)     The only individuals who have been directors or officers of
                 Newco are Terry Owen, Margaret L. Parr and Robert J. Kennedy. 
                 Newco does not have and has never had any employees.
<PAGE>   7
                                     - 7 -


         (r)     Newco is not a partner, co-tenant, joint venturer or otherwise
                 a participant in any partnership, joint venture, co-tenancy or
                 other similar jointly owned business.

         (s)     Neither the Vendors nor Newco have previously granted or
                 agreed to grant any proxy in respect of the Arrangement Shares
                 or entered into any voting trust, vote pooling or other
                 agreement in respect of the Arrangement Shares or any rights
                 attaching thereto.

         (t)     Except as are released prior to Closing, Newco is not a party
                 to nor bound or affected by any agreements, commitments or
                 understandings of any nature whatsoever, written or oral except
                 for this Agreement under which Newco has any outstanding
                 obligations. Except as are released prior to Closing,  Newco is
                 not a party to nor bound by any agreement of guarantee,
                 indemnification, assumption or endorsement or any other like
                 commitment of the obligations, liabilities (contingent or
                 otherwise) or indebtedness of any other person, firm or
                 corporation.

         (u)     Neither Trimac nor Subsidiary is an underwriter, dealer or
                 other person who participates, pursuant to a contractual
                 arrangement, in the distribution of the New Exchangeable
                 Shares sold in reliance on Regulation S ("Regulation S") of
                 the United States Securities Act of 1993 (the "Act").

         (v)     Neither Trimac nor Subsidiary is acquiring the New
                 Exchangeable Shares for the account or benefit of:

                   (i)    any natural person resident in the United States;

                  (ii)    any partnership or corporation organized or
                          incorporated under the laws of the United Sates;

                 (iii)    any estate of which any executor or administrator is
                          a U.S. person;

                  (iv)    any trust of which any trustee is a U.S. person;

                   (v)    any agency or branch of a foreign entity located in
                          the United States;

                  (vi)    any non-discretionary account or similar account
                          (other than an estate or trust) held by a dealer or
                          other fiduciary for the benefit or account of a U.S.
                          person;
<PAGE>   8
                                     - 8 -


                 (vii)    any discretionary account or similar account (other
                          than an estate or trust) held by a dealer or other
                          fiduciary organized, incorporated or (if an
                          individual) resident in the United States; and

                (viii)    any partnership or corporation if:

                          (A)     organized or incorporated under the laws of
                                  any foreign jurisdiction; and

                          (B)     formed by a U.S. person principally for the
                                  purpose of investing in securities not
                                  registered under the Act, unless it is
                                  organized or incorporated, and owned, by
                                  accredited investors (as defined in Rule
                                  501(a) under the Act) who are not natural
                                  persons, estates or trusts.

         (w)     None of the foregoing representations and statements of fact
                 contains any untrue statement of material fact or omits to
                 state any material fact necessary to make any such statement
                 or representation not misleading to a prospective purchaser of
                 the Arrangement Shares seeking full information as to Newco,
                 its respective properties, businesses and affairs.

4.2      The Vendors acknowledge that the certificates representing the New
         Exchangeable Shares will bear a legend in substantially the following
         form:

                 THE SECURITIES EVIDENCED BY THIS CERTIFICATE (OR ITS
                 PREDECESSOR) WERE ORIGINALLY ISSUED IN A TRANSACTION EXEMPT
                 FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF
                 1933 (THE "SECURITIES ACT"), AND MAY NOT BE OFFERED, SOLD,
                 PLEDGED OR OTHERWISE TRANSFERRED IN THE UNITED STATES OR TO,
                 OR FOR THE ACCOUNT OR BENEFIT OF, ANY U.S.  PERSON EXCEPT
                 PURSUANT TO AN AVAILABLE EXEMPTION FROM THE REGISTRATION
                 REQUIREMENTS OF THE SECURITIES ACT AND ALL APPLICABLE STATE
                 SECURITIES LAWS. TERMS USED ABOVE HAVE THE MEANINGS GIVEN THEM
                 IN REGULATION S UNDER THE SECURITIES ACT.
<PAGE>   9
                                     - 9 -


                 PURSUANT TO THAT CERTAIN SHARE PURCHASE AGREEMENT DATED
                 FEBRUARY 13, 1998 BETWEEN THE HOLDER OF THIS CERTIFICATE AND
                 PIONEER NATURAL RESOURCES (CANADA) LTD., THE HOLDER OF THIS
                 CERTIFICATE HAS AGREED THAT IT WILL NOT VOLUNTARILY OFFER,
                 SELL, PLEDGE (WITH CERTAIN EXCEPTIONS), TRANSFER, ASSIGN OR
                 OTHERWISE DISPOSE OF THE SECURITIES REPRESENTED BY THIS
                 CERTIFICATE; PROVIDED, HOWEVER, THAT NOTHING HEREIN SHALL LIMIT
                 SUCH HOLDER'S RIGHT TO RECEIVE SHARES OF COMMON STOCK, PAR
                 VALUE $.01 PER SHARE, OF PIONEER NATURAL RESOURCES COMPANY
                 PURSUANT TO THE PROVISIONS OF THE EXCHANGEABLE SHARES AND
                 RELATED ARRANGEMENTS.

4.3      The Vendors agree that the issuance by Pioneer Canada of New
         Exchangeable Shares is exempt from registration under the United
         States Securities Act of 1933 (the "Act") pursuant to Regulation S
         ("Regulation S") of the Act.

4.4      The Vendors agree that they will not voluntarily offer, sell, pledge,
         transfer, assign or otherwise dispose of the New Exchangeable Shares;
         provided, however, that nothing herein shall limit a Vendor's right to
         receive shares of common stock, par value $.01 per share, of Pioneer
         Natural Resources Company ("Pioneer Common Stock") pursuant to the
         provisions of the New Exchangeable Shares and related arrangements or
         pledging or depositing the New Exchangeable Shares with a Pledge or
         other recipient of the New Exchangeable Shares who is bound by the same
         restrictions imposed on the Vendors pursuant to this Section 4.4.

4.5      Subsidiary agrees to comply with the terms of that certain
         Shareholders Agreement (the "Shareholders Agreement"), dated as of
         September 3, 1997 among Pioneer Natural Resources company, Trimac
         Corporation and Gendis Inc. as if Subsidiary had entered into such
         agreement. With respect to both Trimac and Subsidiary, to the extent 
         that there is any inconsistency between the Shareholders Agreement and
         this Agreement, the terms of this Agreement shall supersede the terms 
         of the Shareholders Agreement.
<PAGE>   10
                                     - 10 -


                                   ARTICLE 5
             PURCHASER'S REPRESENTATIONS, WARRANTIES AND COVENANTS

5.1      The Purchaser represents and warrants to the Vendors that effective on
         the date hereof and at the Closing Date:

         (a)     The Purchaser is a corporation duly continued and subsisting
                 under the laws of the Province of Alberta, and has all
                 requisite corporate power and authority to enter into and
                 perform all of its obligations under this Agreement.

         (b)     This Agreement has been duly executed and delivered by the
                 Purchaser, and the provisions hereof constitute legal, valid
                 and binding obligations of the Purchaser enforceable against
                 it in accordance with their terms.

         (c)     The execution, delivery and performance of this Agreement and
                 the transactions contemplated hereby including the issue of
                 the New Exchangeable Shares have been duly and validly
                 authorized by all requisite action on the part of the
                 Purchaser and the New Exchangeable Shares, when issued
                 pursuant to the terms hereof, will have been validly issued as
                 fully-paid and non-assessable.

         (d)     The consummation of the transactions contemplated herein will
                 not violate, nor be in conflict with, any provision of the
                 Purchaser's Articles of Incorporation or bylaws or any
                 agreement by which it is bound.

5.2      (a)     Purchaser agrees that Trimac shall prepare and file all tax
                 returns, elections or forms which Newco is required to file
                 relating to transactions or events or other matters occurring
                 at or before the Closing Time or in respect of fiscal periods
                 ending at or prior to the Closing Date. The Purchaser shall
                 cause Newco to provide all necessary powers of attorney,
                 information and access to books and records to enable Trimac
                 to prepare and file the returns, elections and forms referred
                 to above. Trimac shall prepare all necessary powers of
                 attorney.

         (b)     Forms T2057 have been executed and filed to make an election
                 pursuant to Subsection 85(1) of the Income Tax Act (Canada)
                 (the "Act") in respect of (i) the acquisition by Newco of
                 shares of Chauvco Resources Ltd., and (ii) the transfer of the
                 Chauvco
<PAGE>   11
                                     - 11 -


                 in the form attached as Schedule "A" hereto. The Purchaser
                 agrees that the Form T2057 shall be filed by Trimac with 
                 Revenue Canada.
 
         (c)     The Purchaser agrees with Trimac that a Form T2057 will be
                 executed by them and filed to make an election pursuant to
                 Subsection 85(1) of the Act in respect of the acquisition by
                 the Purchaser of the Chauvco Resources Ltd. shares from Newco
                 pursuant to the Plan of Arrangement implemented on December 
                 18, 1997, which shall contain the information and be in the 
                 form attached as Schedule "B" hereto. The Purchaser agrees 
                 that the Form T2057 shall be filed by Trimac on behalf of
                 Newco with Revenue Canada.

         (d)     The Purchaser agrees with Trimac that a Form T2057 will be
                 executed by them and filed to make an election pursuant to
                 Subsection 85(1) of the Act in respect of the acquisition by
                 the Purchaser of the Newco Class A Shares, which shall contain
                 the information and be in the form attached as Schedule "C"
                 hereto. The Purchaser agrees that the Form T2057 shall be
                 filed by Trimac with Revenue Canada.

         (e)     The Purchaser agrees with the Subsidiary that a Form T2057
                 will be executed by them and filed to make an election
                 pursuant to Subsection 85(1) of the Act in respect of the
                 acquisition by the Purchaser of the Newco Preferred Shares,
                 which shall contain the information and be in the form
                 attached as Schedule "D" hereto. The Purchaser agrees that the
                 Form T2057 shall be filed by the Subsidiary with Revenue
                 Canada.

         (f)     At the Closing Time the Purchaser shall deliver to the Vendors
                 Forms T2057 in the form attached as Schedule "C" and "D", each
                 duly executed by the Purchaser.

                                   ARTICLE 6
                                    SURVIVAL

6.1      The representations and warranties of the Purchaser and the Vendors
         shall survive the execution of this Agreement and consummation of the
         transactions described herein and shall continue to remain in full
         force and effect. The Covenants of the Purchaser and Vendors shall
         survive the execution of this Agreement and the consummation of the
         transactions described herein and shall continue and remain in full
         force and effect until Trimac and Subsidiary no longer own any New
         Exchangeable Shares or shares of common stock of Pioneer Natural
         Resources Company, into which such New Exchangeable Shares have been
         exchanged.

6.2      The Purchaser shall provide Trimac with reasonable access to the books
         and records of Newco following the Closing Date and shall preserve
         such books and records for a period of seven (7) years from the
         Closing Date.
<PAGE>   12
                                     - 12 -


                                   ARTICLE 7
                                INDEMNIFICATION

7.1      Each of the Vendors jointly and severally covenants and agrees with
         the Purchaser to pay, satisfy, discharge, observe, perform, fulfill,
         indemnify and save harmless the Purchaser, on an after tax basis, from
         and against each of the following (a "Claim"):

         (a)     any claim, demand, action, cause of action, demand, loss,
                 cost, liability or expense (including without limitation,
                 reasonable professional fees and all costs incurred in
                 investigating or pursuing any of the foregoing or any
                 proceeding relating to the foregoing) which may be made or
                 brought against the Purchaser or which it may suffer or incur
                 as a result of or in connection with any non-fulfillment of
                 any covenant or agreement on the part of either of the Vendors
                 under, or any incorrectness in or breach of any representation
                 or warranty of either of the Vendors in, this Agreement, and

         (b)     any liabilities, duties or obligations of Newco arising as a
                 result of or in connection with transactions or events which
                 occurred prior to the Closing Date, including, without
                 limitation:

                   (i)    all debts, obligations, liabilities (including
                          continent liabilities), leases, contracts,
                          commitments or engagements whatsoever,

                  (ii)    all liabilities in respect of income, capital and
                          other taxes and governmental charges and assessments,
                          and

                 (iii)    reasonable professional fees and all costs incurred
                          in investigating or pursuing any of the foregoing or
                          any proceeding relating to the foregoing, and

         (c)     any Purchaser Tax Cost, and all reasonable professional fees
                 and costs incurred in investigating, pursuing or defending
                 against any Purchaser Tax Cost or any proceeding relating
                 thereto.

7.2      NOTICE OF CLAIM OR COMMENCEMENT OF PROCEEDING

         Promptly after receipt by the Purchaser of notice of a Claim or the
         commencement of any action, suit or proceeding in respect thereof and
         any appeal therefrom ("Proceeding") against which it believes it is
         indemnified
<PAGE>   13
                                     - 13 -


         under this Agreement, the Purchaser shall, if a claim in respect
         thereto is to be made against a party under an obligation to indemnify
         the Purchaser (the "Indemnifying Party") under this Agreement, notify
         the Indemnifying Party in writing of such Claim or Proceeding,
         provided, however, that the omission so to notify the Indemnifying
         Party shall not relieve it from any liability which it may have to the
         Purchaser to the extent that the Indemnifying Party is not prejudiced
         by such omission.

7.3      DEFENSE OF CLAIMS.

         (a)     The Indemnifying Party shall, within 30 days after receipt of
                 a notice of Claim or Proceeding given pursuant to Section 7.2,
                 either (1) acknowledge liability, as between the Indemnifying
                 Party and the Purchaser, for such Claim or the amount in
                 controversy in such Proceeding and pay the Purchaser the
                 amount of such Claim or the amount in controversy in such
                 Proceeding in cash or other immediately available funds (or
                 establish by agreement with the Purchaser an alternative
                 payment schedule), (2) acknowledge liability, as between the
                 Indemnifying Party and the Purchaser, for such Claim or the
                 amount in controversy in such Proceeding, disavow the validity
                 of the Claim or Proceeding or the amount thereof and, to the
                 extent set forth in Section 7.3(b), assume the legal defense
                 thereof, or (3) object (or reserve the right to object until
                 additional information is obtained) to the claim for
                 indemnification or the amount thereof, setting forth the
                 grounds therefor in reasonable detail; provided that, if the
                 Indemnifying Party objects (or reserves its right to object)
                 within such 30-day period as provided in this Section 7.3,
                 then the Purchaser may bring suit (in the same Proceeding or
                 otherwise) to resolve the dispute and, pending final
                 resolution of such dispute, the Purchaser may proceed as
                 though the Indemnifying Party had responded in accordance with
                 clause (1) above. If the Indemnifying Party does not respond
                 to the Purchaser as provided in this Section 7.3 within such
                 30-day period, the Indemnifying Party shall be deemed to have
                 acknowledged its liability for such indemnification claim in
                 accordance with clause (1) above and the Purchaser may
                 exercise any and all of its rights under applicable law to
                 collect such amount.

         (b)     If any such Proceeding shall be brought against the Purchaser
                 and it shall notify the Indemnifying Party thereof in
                 accordance with Section 7.2, the Indemnifying Party shall, if
                 it shall have responded to such notice in accordance with
                 clause (a)(2) above, be entitled (1)
<PAGE>   14
                                     - 14 -


                 in the case of a Claim in respect of a Purchaser Tax Cost
                 arising out of a proceeding involving other issues for which
                 Purchaser is not indemnified hereunder, to elect to
                 participate (directly or through counsel reasonably
                 satisfactory to Purchaser) in the portion of the Proceedings
                 related to the issue constituting the Purchaser Tax Cost,
                 subject to the control of Purchaser over such Proceeding, or
                 (2) in all other cases, to elect to assume the legal defense
                 thereof with counsel reasonably satisfactory to the Purchaser.
                 After notice from the Indemnifying Party to the Purchaser of
                 its election to assume the defense of such claim or such
                 action described in clause (2) hereof, the Indemnifying Party
                 shall not be liable to the Purchaser under this Article for
                 any attorney's fees or other expenses (except reasonable costs
                 of investigation) subsequently incurred by the Purchaser in
                 connection with the defense thereof. In all other cases
                 described in clause (a)(2), the Purchaser may require the
                 Indemnifying Party to reimburse it on a current basis for its
                 reasonable expenses of investigation, reasonable attorneys'
                 and accountants' fees and expenses and reasonable
                 out-of-pocket expenses incurred in the defense thereof and the
                 Indemnifying Party shall be bound by the result obtained with
                 respect thereto by the Purchaser.

         (c)     An Indemnifying Party will not, without prior written consent
                 of the Purchaser (which consent shall not be unreasonably
                 withheld), settle or compromise or consent to the entry of any
                 judgment with respect to any pending or threatened Claim or
                 Proceeding in respect of which indemnification or contribution
                 may be sought hereunder (whether or not the Purchaser is an
                 actual or potential party to such Claim or Proceeding) unless
                 such settlement, compromise or consent includes an
                 unconditional release of the Purchaser from all liability
                 arising out of such Claim or Proceeding. If the Indemnifying
                 Party has responded to the Purchaser pursuant to clause (a)(1)
                 above (not including a deemed response under the proviso
                 contained in 7.3(a)(3)), the Purchaser may settle or
                 compromise or consent to the entry of any judgment with
                 respect to the Claim or Proceeding that was the subject of
                 notice to the Indemnifying Party pursuant to this Article
                 without the consent of the Indemnifying Party. The Purchaser
                 will not otherwise, without the prior written consent of the
                 Indemnifying Party (which consent shall not be unreasonably
                 withheld), settle or compromise or consent to the entry of any
                 judgment with respect to any pending or threatened Claim or
                 Proceeding, but, if such Claim or Proceeding is settled or
<PAGE>   15
                                     - 15 -


                 compromised or if there is entered any judgment with respect
                 to any such Claim or Proceeding, in either case with the
                 consent of the Indemnifying Party, or if there be a final
                 judgment of the plaintiff in any such Claim or Proceeding, the
                 Indemnifying Party agrees to indemnify and hold harmless the
                 Purchaser from and against any loss or liability by reason of
                 such settlement, compromise or judgment.

7.4      REFUND OF AMOUNTS

         If any person becomes entitled to a refund (whether by payment,
         credit, offset or otherwise) of all or a portion of any amount
         relating to a Claim or Proceeding for which an Indemnifying Party has,
         by payment, indemnified the Purchaser, then an amount equal to the
         refund, together with any interest received on such refund (net of any
         Tax payable on such interest), shall be paid by the Purchaser to the
         Indemnifying Party promptly after receipt of payment of the refund or
         notice from the relevant governmental authority of such credit, offset
         or other refund mechanism, as the case may be.

7.5      LIMITATION OF INDEMNITY

         The joint and several indemnity of the Vendors in respect of any
         Purchaser Tax Cost shall be limited to the proportion of such Purchaser
         Tax Cost that the number of New Exchangeable Shares issued hereunder is
         to the total number of New Exchangeable Shares issued pursuant to this
         Agreement and the similar agreement entered into as of the date hereof
         with 398215 Alberta Ltd. and Guy J. Turcotte. Notwithstanding anything
         contained in this Article 7, the joint and several indemnity of the
         Vendors in respect of any Purchaser Tax Cost arising under any
         legislation or regulation of a jurisdiction other than Canada or a
         province or territory thereof, shall not exceed the sum of $10,112,757
         United States dollars. 

                                   ARTICLE 8
                                    EXPENSES

8.1      The Vendors jointly and severally agree to reimburse the Purchaser for
         all out of pocket expenses incurred by the Purchaser (including fees
         and disbursements of counsel and all tax advisors) in connection with
         the transaction contemplated herein including without limitation in
         connection with the preparation, execution and performance of this
         Agreement within 10 business days after receipt of a written invoice
         with respect thereto.  In respect of expenses which relate to this
         Agreement and to other similar
<PAGE>   16
                                     - 16 -


         agreements entered into with respect to other holders of Exchangeable
         Shares, the Vendors shall reimburse Purchaser in the proportion which
         the number of Exchangeable Shares issued hereunder is to the total
         number of Exchangeable Shares issued pursuant to all such similar
         agreements.

                                   ARTICLE 9
                                    CLOSING

9.1      Closing shall take place at the Closing Time on the Closing Date at
         the offices of MacKimmie Matthews, 700, 401 - 9th Avenue S.W.,
         Calgary, Alberta, or at such other place as the parties hereto may
         agree upon.

9.2      At Closing, the Vendors shall deliver to the Purchaser:


         (a)     a certified copy of the resolution of the directors of Newco
                 approving the transfer of the Newco Shares;

         (b)     certificates for the Newco Shares duly endorsed in blank for
                 transfer;

         (c)     written resignations from all directors and officers of Newco;
                 and

         (d)     a certificate, dated as of the Closing Date, executed by each
                 of the Vendors, to the effect that the representations and
                 warranties made in Section 4.1 are true and correct in all
                 material respects at and as of the Closing Date and that
                 Vendors have complied with all Agreements herein required to
                 be complied with at and as of the Closing Date.

9.3      At the Closing Time on the Closing Date, the Purchaser shall deliver
         to the Vendors certificates representing the New Exchangeable Shares.

                                   ARTICLE 10
                               CLOSING CONDITIONS

10.1     The obligation of the Purchaser to complete the purchase of the Newco
         Shares is subject to the conditions precedent that:

         (a)     the Vendors shall have performed or complied in all material
                 respects with each of the terms, covenants and conditions of
                 this Agreement to be performed or complied with by the Vendors
                 at or prior to the Closing Date;
<PAGE>   17
                                     - 17 -


         (b)     the approval of the Toronto Stock Exchange and all other
                 necessary regulatory approvals for the completion of the
                 transaction shall have been obtained; and

         (c)     the registration statement on Form S-3 registering the shares
                 of Pioneer Common Stock underlying the New Exchangeable Shares
                 shall have been declared effective by the United States
                 Securities and Exchange Commission.

The conditions in the Section 10.1 are for the sole benefit of the Purchaser
and may be waived, in whole or in part, by written notice to the Vendors.

10.2     The obligation of the Vendors to complete the sale of the Newco Shares
         is subject to the condition precedent that the Purchaser shall have
         performed or complied in all material respects with each of the terms,
         covenants and conditions of this Agreement to be performed or complied
         with by Purchaser at or prior to the Closing Date, which condition is
         for the sole benefit of the Vendors and may be waived, in whole or in
         part, by written notice to the Purchaser.

10.3     Purchaser shall cause its counsel to apply for all required regulatory
         approvals.

                                   ARTICLE 11
                                 MISCELLANEOUS

11.1     This Agreement shall enure to the benefit of and be binding upon the
         parties hereto and their respective successors and permitted assigns.

11.2     All obligations of the Vendors hereunder shall be joint and several.

11.3     Any direction, notice, request, delivery or demand hereunder shall be
         in writing, shall be hand delivered or telecopied and shall be deemed
         to have been received on the date of delivery. Either party may change
         its address by notice given in the manner aforesaid.

         (a)     if to the Purchaser, addressed to:

                 Pioneer Natural Resources (Canada) Ltd.
                 c/o Pioneer Natural Resources Company
                 1400 Williams Square West
                 5205 - N O'Connor Blvd.
<PAGE>   18
                                     - 18 -


                 Irving, Texas
                 75039-3746
                 Attention:  General Counsel

         (b)     if to Trimac, addressed to:
                 Trimac Corporation
                 2100, 800 - 5th Avenue S.W.
                 Calgary, Alberta
                 T2P 2P9
                Attention: T.J. Owen, Vice-President and Chief Financial Officer

         (c)     if to Subsidiary

                 761795 Alberta Ltd.
                 2100, 800 - 5th Avenue S.W.
                 Calgary, Alberta
                 T2P 2P9
                 Attention: T.J. Owen, President

11.4     Time shall be of the essence.

11.5     No amendment or variation of this Agreement shall be of any force or
         effect unless the same be reduced to writing and duly executed by all
         parties hereto.

11.6     Each of the parties shall at any time, and from time to time
         hereafter, take any and all steps, and execute, acknowledge and
         deliver to the other party, any and all further instruments and
         assurances that the other party may reasonably require for the purpose
         of giving full force and effect to the provisions of this Agreement.

11.7     Neither party may assign in whole or in part any of its interest,
         rights or obligations hereunder without the prior written agreement of
         the other party hereto except as expressly provided herein.
<PAGE>   19
                                     - 19 -


11.8     This Agreement may be executed in counterparts, each of which when so
         executed shall be deemed to be an original, and such counterparts
         together shall constitute one and the same instrument, which shall be
         sufficiently evidenced by such original counterparts.

EXECUTED AND DELIVERED.

                                   PIONEER NATURAL RESOURCES (CANADA) LTD.

                                   By:                                       
                                      ---------------------------------------

                                   TRIMAC CORPORATION

                                   By:                                       
                                      ---------------------------------------

                                   761795 ALBERTA LTD.

                                   By:                                       
                                      ---------------------------------------
<PAGE>   20
                                   SCHEDULE A





<PAGE>   21
                                   SCHEDULE B





<PAGE>   22
                                   SCHEDULE C






<PAGE>   1
                                                               EXHIBIT 10.59




                            SHARE PURCHASE AGREEMENT
                               February 13, 1998

BETWEEN

                 PIONEER NATURAL RESOURCES (CANADA) LTD., a body corporate
                 continued under the laws of Alberta ("PURCHASER")

                                      AND

                 398215 ALBERTA LTD., a body corporate incorporated under the
                 laws of the Province of Alberta ("398215")

                                      AND

                 GUY J. TURCOTTE, an individual resident in the Province of
                 Alberta ("TURCOTTE")

RECITALS

A.       398215 is the legal and beneficial holder of all outstanding shares of
         760551 Alberta Ltd. ("Newco"), and Turcotte is the legal and
         beneficial holder of certain debt of Newco in the principal amount of
         $3,781,300 ("Newco Debt");

B.       The Purchaser desires to purchase and the Vendors desire to sell the
         Newco Shares and Newco Debt on the terms set out in this Agreement;

C.       The only asset of Newco is a total of 581,064 Exchangeable Shares in
         the capital of the Purchaser.

THE PARTIES AGREE AS FOLLOWS.

                                   ARTICLE 1

                                 INTERPRETATION

1.1      In this Agreement, including the premises hereto and this section,
         unless the context otherwise requires, the following terms shall have
         the following respective meanings:

         "AGREEMENT" means this Agreement and any schedules attached hereto and
         any amendments hereof;
<PAGE>   2
                                     -2-


         "ARRANGEMENT SHARES" means the 581,064 Exchangeable Shares held by
         Newco;

         "CLOSING" means the completion of the transactions contemplated by the
         Agreement;

         "CLOSING DATE" means February 13, 1998 or such other date as the
         parties hereto may agree;

         "CLOSING TIME" means 2:00 p.m., Calgary Time, or such other time as
         the parties hereto may agree, on the Closing Date;

         "NEW EXCHANGEABLE SHARES" means the Exchangeable Shares to be issued
         to the Vendors pursuant to this Agreement;

         "NEWCO" means 760551 Alberta Ltd., an Alberta corporation;

         "NEWCO DEBT" means $3,781,300 principal amount of debt owing by Newco
         to Turcotte;

         "NEWCO SHARES" means 1,100 Newco Class A Common Shares;

         "PURCHASER TAX COST" means any liability for any Tax which (i) is
         suffered or incurred, directly or indirectly, by Purchaser, and (ii)
         would not have been so suffered or incurred had the transactions
         contemplated by this Agreement not taken place or had the Arrangement
         Shares not been cancelled in connection with the winding up or
         dissolution of Newco. For purposes of the foregoing, a Tax shall be
         considered to be suffered or incurred by Purchaser indirectly if such
         Tax is suffered or incurred by any person related to Purchaser within
         the meaning of Section 954(d)(3) of the United States Internal Revenue
         Code of 1986, as amended, assuming for such purpose that Purchaser is
         a "controlled foreign corporation" within the meaning of Section 957
         of said Code.

         "TAX" means (i) any Canadian domestic, United States or other foreign
         net income, alternative or add-on minimum, gross income, gross
         receipts, sales, use, ad valorem, value added, transfer, franchise,
         profits, license, withholding, payroll, employment, excise,
         production, severance, stamp, occupation, premium, property,
         environment, or windfall profit tax, custom, duty or other tax,
         governmental fee or other like assessment or charge of any kind
         whatsoever, together with any interest and/or any penalty, addition to
         tax or additional amount imposed by any taxing authority, and (ii) any
         liability of a person for the payment of any amounts of the type
         described in
<PAGE>   3
                                     - 3 -


         clause (i) as a result of being a member of an affiliated or
         consolidated group or arrangement whereby liability of such person for
         the payment of such amounts was determined or taken into account with
         reference to the liability of any other person for any period.

         "VENDORS" means collectively, 398215 and Turcotte.

1.2      Headings of the articles or sections hereof are inserted for
         convenience of reference only and shall not affect the construction or
         interpretation of this Agreement.

1.3      In this Agreement, words importing the singular number only shall
         include the plural and vice versa, and words importing the masculine
         gender shall include the feminine and neuter gender, and words
         importing persons shall include provincial or federal companies,
         corporations, partnerships, syndicates, trusts and any number or
         aggregate of persons, all as the context may require.

1.4      All dollar amounts in this Agreement are expressed in Canadian
         dollars.

1.5      This Agreement and all amendments, modifications, alterations or
         supplements thereto shall, in all respects, be subject to and
         interpreted, construed and enforced in accordance with the laws of the
         Province of Alberta. Each party hereto submits to and accepts the
         jurisdiction of the Courts of the Province of Alberta for all purposes
         hereof.

                                   ARTICLE 2

                                 SALE OF SHARES

2.1      Subject to the terms and conditions of this Agreement, the Vendors
         agree to sell, assign, transfer and convey to the Purchaser and the
         Purchaser agrees to purchase from the Vendors, on the Closing Date,
         the Newco Shares and Newco Debt.

                                   ARTICLE 3

                                 PURCHASE PRICE

3.1      In consideration for the Newco Shares and Newco Debt, the Purchaser
         shall issue to the Vendors an aggregate of 581,064 New Exchangeable
         Shares. The purchase consideration shall be allocated between the
         Vendors as follows:
<PAGE>   4
                                     - 4 -



             398215      462,898 New Exchangeable Shares

             Turcotte    118,166 New Exchangeable Shares

                                   ARTICLE 4

                    VENDOR'S REPRESENTATIONS AND WARRANTIES

4.1      Each of the Vendors jointly and severally represents and warrants to
         the Purchaser as follows effective on the date hereof and at the
         Closing Date:

         (a)     Newco is a corporation duly incorporated and subsisting under
                 the laws of the Province of Alberta and has all requisite
                 corporate power and authority to own the Arrangement Shares.

         (b)     The authorized and issued share capital of Newco consists of:

                   (i)    an unlimited number of Class A Common Shares of which
                          1,100 are issued and outstanding as fully paid and
                          non-assessable shares; and

                  (ii)    an unlimited number of Class B Common Shares, none of
                          which have been issued;

                 (iii)    an unlimited number of Class A Preferred Shares none
                          of which have been issued;

         (c)     398215 is the holder of record and the beneficial owner of the
                 Newco Shares and Turcotte is the holder of record and
                 beneficial owner of the Newco Debt, which collectively
                 represent all of the issued and outstanding shares in the
                 capital of Newco and outstanding debt of Newco and the Vendors
                 are and on the Closing Date will be the owner of all such
                 Newco Shares and Newco Debt with good and marketable title
                 thereto free and clear of any option, security interest, lien,
                 charge, encumbrance, hypothecation, claim or right of others
                 (other than the rights of the Purchaser hereunder).

         (d)     Each of the Vendors has the legal right, power and authority
                 to sell, assign and transfer the Newco Shares and Newco Debt
                 being sold by it hereunder free and clear of any option,
                 security interest, lien, charge, encumbrance, hypothecation,
                 claim or right of others (other than the rights of the
                 Purchaser hereunder).
<PAGE>   5
                                     - 5 -



         (e)     There are no outstanding agreements, options, warrants, rights
                 of conversion or other rights pursuant to which Newco is or
                 may become obligated to issue any shares, or securities
                 convertible or exchangeable into shares, and there are no
                 outstanding obligations, understandings or commitments of
                 Newco to repurchase, redeem or otherwise acquire any
                 outstanding shares of its capital or restricting its ability
                 to issue shares.

         (f)     Newco is the beneficial owner of the Arrangement Shares, free
                 and clear of any option, security interest, lien, charge,
                 encumbrance, claim or right of others.

         (g)     Effective on the Closing Date, Newco will have no liabilities,
                 (whether actual, accrued, potential, contingent or otherwise)
                 other than the Newco Debt.

         (h)     From the date of its incorporation until the Closing Date
                 Newco has not carried on any business or owned any assets,
                 other than the Arrangement Shares and common shares of Chauvco
                 Resources International Ltd.

         (i)     The corporate records and minute books of Newco are complete
                 and accurate in all material aspects.

         (j)     398215 is a corporation validly subsisting under the laws of
                 the Province of Alberta, with the requisite corporate power
                 and authority to enter into and perform all of its obligations
                 under this Agreement and the execution, delivery and
                 performance of this Agreement and the transactions
                 contemplated hereby have been duly and validly authorized by
                 all requisite corporate action on the part of 398215.

         (k)     The entering into of this Agreement by 398215 and Turcotte and
                 the completion of the transactions contemplated hereby will
                 not result in the violation of any of the terms and provisions
                 of the constating documents or by-laws of 398215 or Newco or
                 of any indenture or other agreement to which Turcotte, 398215
                 or Newco is a party.

         (l)     The entering into this Agreement by the Vendors and the
                 completion of the transactions contemplated hereby will not
                 result in the violation of any law or regulation of Canada or
                 of the Province of Alberta.
<PAGE>   6
                                     - 6 -



         (m)     This Agreement has been duly executed and delivered by the
                 Vendors and is a valid and binding obligation of each of the
                 Vendors enforceable against them in accordance with its terms.

         (n)     There is no action, suit, litigation, arbitration proceeding
                 or governmental proceeding including appeals and applications
                 for review, in which Newco is a party, either as plaintiff,
                 defendant, applicant, respondent or any other capacity
                 whatsoever. There are no outstanding orders of any court,
                 governmental agency or instrumentality, to which Newco, 398215
                 or Turcotte is subject affecting, in any material respect, the
                 business, prospects, properties or condition (financial or
                 otherwise) of Newco or the ability of the Vendors to
                 consummate the transactions contemplated hereby.

         (o)     Each of the Vendors is not a non-resident of Canada within the
                 meaning of the Income Tax Act (Canada).  398215 is not a
                 corporation incorporated under the laws of the United States.

         (p)     The only individuals who have been directors or officers of
                 Newco are Daryl Refuik and Guy Turcotte. Newco does not have 
                 and has never had any employees.

         (q)     Newco is not a partner, co-tenant, joint venturer or otherwise
                 a participant in any partnership, joint venture, co-tenancy or
                 other similar jointly owned business.

         (r)     Neither the Vendors nor Newco have previously granted or
                 agreed to grant any proxy in respect of the Arrangement Shares
                 or entered into any voting trust, vote pooling or other
                 agreement in respect of the Arrangement Shares or any rights
                 attaching thereto.

         (s)     Except as are released prior to Closing, Newco is not a party 
                 to nor bound or affected by any agreements, commitments or
                 understandings of any nature whatsoever, written or oral except
                 for this Agreement. Except as are released prior to Closing,
                 Newco is not a party to nor bound by any agreement of
                 guarantee, indemnification, assumption or endorsement or any
                 other like commitment of the obligations, liabilities
                 (contingent or otherwise) or indebtedness of any other person,
                 firm or corporation.

         (t)     Neither 398215 nor Turcotte is an underwriter, dealer or other
                 person who participates, pursuant to a contractual
                 arrangement, in the distribution of the New Exchangeable
                 Shares sold in reliance on
<PAGE>   7
                                     - 7 -


                 Regulation S ("Regulation S") of the United States Securities
                 Act of 1993 (the "Act").

         (u)     Neither 398215 nor Turcotte is acquiring the New Exchangeable
                 Shares for the account or benefit of:

                   (i)    any natural person resident in the United States;

                  (ii)    any partnership or corporation organized or
                          incorporated under the laws of the United Sates;

                 (iii)    any estate of which any executor or administrator is
                          a U.S. person;

                   (v)    any trust of which any trustee is a U.S. person;

                  (vi)    any agency or branch of a foreign entity located in
                          the United States;

                 (vii)    any non-discretionary account or similar account
                          (other than an estate or trust) held by a dealer or
                          other fiduciary for the benefit or account of a U.S.
                          person;

                (viii)    any discretionary account or similar account (other
                          than an estate or trust) held by a dealer or other
                          fiduciary organized, incorporated or (if an
                          individual) resident in the United States; and

                  (ix)    any partnership or corporation if:

                          (A)     organized or incorporated under the laws of 
                                  any foreign jurisdiction; and

                          (B)     formed by a U.S. person principally for the
                                  purpose of investing in securities not
                                  registered under the Act, unless it is
                                  organized or incorporated, and owned, by
                                  accredited investors (as defined in Rule
                                  501(a) under the Act) who are not natural
                                  persons, estates or trusts.

         (v)     None of the foregoing representations and statements of fact
                 contains any untrue statement of material fact or omits to
                 state any material fact necessary to make any such statement
                 or representation not misleading to a prospective purchaser of
                 the Arrangement Shares
<PAGE>   8
                                     - 8 -


                 seeking full information as to Newco, its respective
                 properties, businesses and affairs.

4.2      The Vendors acknowledge that the certificates representing the New
         Exchangeable Shares will bear a legend in substantially the following
         form:

                 THE SECURITIES EVIDENCED BY THIS CERTIFICATE (OR ITS
                 PREDECESSOR) WERE ORIGINALLY ISSUED IN A TRANSACTION EXEMPT
                 FROM REGISTRATION UNDER THE UNITED STATES SECURITIES ACT OF
                 1933 (THE "SECURITIES ACT"), AND MAY NOT BE OFFERED, SOLD,
                 PLEDGED OR OTHERWISE TRANSFERRED IN THE UNITED STATES OR TO,
                 OR FOR THE ACCOUNT OR BENEFIT OF, ANY U.S.  PERSON EXCEPT
                 PURSUANT TO AN AVAILABLE EXEMPTION FROM THE REGISTRATION
                 REQUIREMENTS OF THE SECURITIES ACT AND ALL APPLICABLE STATE
                 SECURITIES LAWS. TERMS USED ABOVE HAVE THE MEANINGS GIVEN THEM
                 IN REGULATION S UNDER THE SECURITIES ACT.

                 PURSUANT TO THAT CERTAIN SHARE PURCHASE AGREEMENT DATED
                 FEBRUARY 13, 1998 BETWEEN THE HOLDER OF THIS CERTIFICATE AND
                 PIONEER NATURAL RESOURCES (CANADA) LTD., THE HOLDER OF THIS
                 CERTIFICATE HAS AGREED THAT IT WILL NOT VOLUNTARILY OFFER,
                 SELL, PLEDGE (WITH CERTAIN EXCEPTIONS), TRANSFER, ASSIGN OR 
                 OTHERWISE DISPOSE OF THE SECURITIES REPRESENTED BY THIS 
                 CERTIFICATE; PROVIDED, HOWEVER, THAT NOTHING HEREIN SHALL LIMIT
                 SUCH HOLDER'S RIGHT TO RECEIVE SHARES OF COMMON STOCK, PAR 
                 VALUE $.01 PER SHARE, OF PIONEER NATURAL RESOURCES COMPANY 
                 PURSUANT TO THE PROVISIONS OF THE EXCHANGEABLE SHARES AND 
                 RELATED ARRANGEMENTS.
<PAGE>   9
                                     - 9 -



4.3      The Vendors agree that the issuance by Pioneer Canada of New
         Exchangeable Shares is exempt from registration under the United
         States Securities Act of 1933 (the "Act") pursuant to Regulation S
         ("Regulation S") of the Act.

4.4      The Vendors agree that they will not voluntarily offer, sell, pledge,
         transfer, assign or otherwise dispose of the New Exchangeable Shares;
         provided, however, that nothing herein shall limit a Vendor's right to
         receive shares of common stock, par value $.01 per share, of Pioneer
         Natural Resources Company ("Pioneer Common Stock") pursuant to the
         provisions of the New Exchangeable Shares and related arrangements or
         pledging or depositing the New Exchangeable Shares with a Pledgee or
         other recipient of the New Exchangeable Shares who is bound by the
         same restrictions imposed on the Vendors pursuant to this Section 4.4.

4.5      398215 agrees to comply with the terms of that certain Shareholders
         Agreement (the "Shareholders Agreement"), dated as of September 3,
         1997 between Pioneer Natural Resources Company, and Turcotte as if
         398215 had entered into such agreement. With respect to both Turcotte
         and 398215, to the extent that there is any inconsistency between the
         Shareholders Agreement and this Agreement , the terms of this
         Agreement shall supersede the terms of the Shareholders Agreement

                                   ARTICLE 5

             PURCHASER'S REPRESENTATIONS, WARRANTIES AND COVENANTS

5.1      The Purchaser represents and warrants to the Vendor that effective on
         the date hereof and at the Closing Date:

         (a)     The Purchaser is a corporation duly continued and subsisting
                 under the laws of the Province of Alberta, and has all
                 requisite corporate power and authority to enter into and
                 perform all of its obligations under this Agreement.

         (b)     This Agreement has been duly executed and delivered by the
                 Purchaser, and the provisions hereof constitute legal, valid
                 and binding obligations of the Purchaser enforceable against
                 it in accordance with their terms.

         (c)     The execution, delivery and performance of this Agreement and
                 the transactions contemplated hereby including the issue of
                 the New Exchangeable Shares have been duly and validly
                 authorized by all requisite action on the part of the
                 Purchaser and the New Exchangeable Shares, when issued
                 pursuant to the terms hereof, will have been validly issued as
                 fully-paid and non-assessable.
<PAGE>   10
                                     - 10 -



         (d)     The consummation of the transactions contemplated herein will
                 not violate, nor be in conflict with, any provision of the
                 Purchaser's constating documents or bylaws or any agreement by
                 which it is bound.

5.2      (a)     Purchaser agrees that 398215 shall prepare and file all tax
                 returns, elections or forms which Newco is required to file
                 relating to transactions or events or other matters occurring
                 at or before the Closing Time or in respect of fiscal periods
                 ending at or prior to the Closing Date. The Purchaser shall
                 cause Newco to provide all necessary powers of attorney,
                 information and access to books and records to enable 398215
                 to prepare and file the returns, elections and forms referred
                 to above. 398215 shall prepare all necessary powers of
                 attorney.

          (b)    Form T2057 has been executed to make an election pursuant to
                 Subsection 85(1) of the Income Tax Act (Canada) (the "Act") in
                 respect of the acquisition by Newco of shares of Chauvco
                 Resources Ltd. in the form attached as Schedule "A" hereto. The
                 Purchaser agrees with 398215 that the Form T2057 shall be filed
                 by 398215 with Revenue Canada.

          (c)    The Purchaser agrees with 398215 that a Form T2057 will be
                 executed by them and filed to make an election pursuant to
                 Subsection 85(1) of the Act in respect of the acquisition by
                 the Purchaser of the Chauvco Resources Ltd. shares from Newco
                 pursuant to the Plan of Arrangement implemented on December 18,
                 1997, which shall contain the information and be in the form
                 attached as Schedule "B" hereto. The Purchaser agrees that the
                 Form T2057 shall be filed by 398215 on behalf of Newco with
                 Revenue Canada.

         (d)     The Purchaser agrees with Trimac that a Form T2057 will be
                 executed by them and filed to make an election pursuant to
                 Subsection 85(1) of the Act in respect of the acquisition by
                 the Purchaser of the Newco Shares, which shall contain the
                 information and be in the form attached as Schedule "C"
                 hereto.  The Purchaser agrees that the Form T2057 shall be
                 filed by 398215 with Revenue Canada.

         (e)     At the Closing Time the Purchaser shall deliver to the Vendors
                 Form T2057 in the form attached as Schedule "C", each duly
                 executed by the Purchaser.

                                   ARTICLE 6

                                    SURVIVAL

6.1      The representations and warranties of the Purchaser and the Vendors
         shall survive the execution of this Agreement and consummation of the
<PAGE>   11
                                     - 11 -


         transactions described herein and shall continue to remain in full
         force and effect. The Covenants of the Purchaser and Vendors shall
         survive the execution of this Agreement and the consummation of the
         transactions described herein and shall continue and remain in full
         force and effect until 398215 and Turcotte no longer own any New
         Exchangeable Shares or shares of common stock of Pioneer Natural
         Resources Company, into which such New Exchangeable Shares have been
         exchanged.

6.2      The Purchaser shall provide 398215 with reasonable access to the books
         and records of Newco following the Closing Date and shall preserve
         such books and records for a period of seven (7) years from the
         Closing Date.

                                   ARTICLE 7

                                INDEMNIFICATION

7.1      Each of the Vendors jointly and severally covenants and agrees with
         the Purchaser to pay, satisfy, discharge, observe, perform, fulfill,
         indemnify and save harmless the Purchaser, on an after tax basis, from
         and against each of the following (a "Claim"):

         (a)     any claim, demand, action, cause of action, demand, loss,
                 cost, liability or expense (including without limitation,
                 reasonable professional fees and all costs incurred in
                 investigating or pursuing any of the foregoing or any
                 proceeding relating to the foregoing) which may be made or
                 brought against the Purchaser or which it may suffer or incur
                 as a result of or in connection with any non-fulfillment of
                 any covenant or agreement on the part of either of the Vendors
                 under, or any incorrectness in or breach of any representation
                 or warranty of either of the Vendors in, this Agreement, and

         (b)     any liabilities, duties or obligations of Newco arising as a
                 result of or in connection with transactions or events which
                 occurred prior to the Closing Date, including, without
                 limitation:

                   (i)    all debts, obligations, liabilities (including
                          continent liabilities), leases, contracts,
                          commitments or engagements whatsoever,

                  (ii)    all liabilities in respect of income, capital and
                          other taxes and governmental charges and assessments,
                          and
<PAGE>   12
                                     - 12 -



                 (iii)    reasonable professional fees and all costs incurred
                          in investigating or pursuing any of the foregoing or
                          any proceeding relating to the foregoing, and

         (c)     any Purchaser Tax Cost, and all reasonable professional fees
                 and costs incurred in investigating, pursuing or defending
                 against any Purchaser Tax Cost or any proceeding relating
                 thereto.

7.2      NOTICE OF CLAIM OR COMMENCEMENT OF PROCEEDING      Promptly after
         receipt by the Purchaser of notice of a Claim or the commencement of
         any action, suit or proceeding in respect thereof and any appeal
         therefrom ("Proceeding") against which it believes it is indemnified
         under this Agreement, the Purchaser shall, if a claim in respect
         thereto is to be made against a party under an obligation to indemnify
         the Purchaser (the "Indemnifying Party") under this Agreement, notify
         the Indemnifying Party in writing of such Claim or Proceeding,
         provided, however, that the omission so to notify the Indemnifying
         Party shall not relieve it from any liability which it may have to the
         Purchaser to the extent that the Indemnifying Party is not prejudiced
         by such omission.

7.3      DEFENSE OF CLAIMS.

         (a)     The Indemnifying Party shall, within 30 days after receipt of
                 a notice of Claim or Proceeding given pursuant to Section 7.2,
                 either (1) acknowledge liability, as between the Indemnifying
                 Party and the Purchaser, for such Claim or the amount in
                 controversy in such Proceeding and pay the Purchaser the
                 amount of such Claim or the amount in controversy in such
                 Proceeding in cash or other immediately available funds (or
                 establish by agreement with the Purchaser an alternative
                 payment schedule), (2) acknowledge liability, as between the
                 Indemnifying Party and the Purchaser, for such Claim or the
                 amount in controversy in such Proceeding, disavow the validity
                 of the Claim or Proceeding or the amount thereof and, to the
                 extent set forth in Section 7.3(b), assume the legal defense
                 thereof, or (3) object (or reserve the right to object until
                 additional information is obtained) to the claim for
                 indemnification or the amount thereof, setting forth the
                 grounds therefor in reasonable detail; provided that, if the
                 Indemnifying Party objects (or reserves its right to object)
                 within such 30-day period as provided in this Section 7.3,
                 then the Purchaser may bring suit (in the same Proceeding or
                 otherwise) to resolve the dispute and, pending final
                 resolution of such dispute, the Purchaser may proceed as
                 though the
<PAGE>   13
                                     - 13 -


                 Indemnifying Party had responded in accordance with clause (1)
                 above. If the Indemnifying Party does not respond to the
                 Purchaser as provided in this Section 7.3 within such 30-day
                 period, the Indemnifying Party shall be deemed to have
                 acknowledged its liability for such indemnification claim in
                 accordance with clause (1) above and the Purchaser may
                 exercise any and all of its rights under applicable law to
                 collect such amount.

         (b)     If any such Proceeding shall be brought against the Purchaser
                 and it shall notify the Indemnifying Party thereof in
                 accordance with Section 7.2, the Indemnifying Party shall, if
                 it shall have responded to such notice in accordance with
                 clause (a)(2) above, be entitled (1) in the case of a Claim in
                 respect of a Purchaser Tax Cost arising out of a proceeding
                 involving other issues for which Purchaser is not indemnified
                 hereunder, to elect to participate (directly or through
                 counsel reasonably satisfactory to Purchaser) in the portion
                 of the Proceedings related to the issue constituting the
                 Purchaser Tax Cost, subject to the control of Purchaser over
                 such Proceeding, or (2) in all other cases, to elect to assume
                 the legal defense thereof with counsel reasonably satisfactory
                 to the Purchaser. After notice from the Indemnifying Party to
                 the Purchaser of its election to assume the defense of such
                 claim or such action described in clause (2) hereof, the
                 Indemnifying Party shall not be liable to the Purchaser under
                 this Article for any attorney's fees or other expenses (except
                 reasonable costs of investigation) subsequently incurred by
                 the Purchaser in connection with the defense thereof. In all
                 other cases described in clause (a)(2), the Purchaser may
                 require the Indemnifying Party to reimburse it on a current
                 basis for its reasonable expenses of investigation, reasonable
                 attorneys' and accountants' fees and expenses and reasonable
                 out-of-pocket expenses incurred in the defense thereof and the
                 Indemnifying Party shall be bound by the result obtained with
                 respect thereto by the Purchaser.

         (c)     An Indemnifying Party will not, without prior written consent
                 of the Purchaser (which consent shall not be unreasonably
                 withheld), settle or compromise or consent to the entry of any
                 judgment with respect to any pending or threatened Claim or
                 Proceeding in respect of which indemnification or contribution
                 may be sought hereunder (whether or not the Purchaser is an
                 actual or potential party to such Claim or Proceeding) unless
                 such settlement, compromise or consent includes an
                 unconditional release of the Purchaser from all liability
                 arising out of such Claim or Proceeding. If the Indemnifying
                 Party
<PAGE>   14
                                     - 14 -


                 has responded to the Purchaser pursuant to clause (a)(1) above
                 (not including a deemed response under the proviso contained
                 in 7.3(a)(3)), the Purchaser may settle or compromise or
                 consent to the entry of any judgment with respect to the Claim
                 or Proceeding that was the subject of notice to the
                 Indemnifying Party pursuant to this Article without the
                 consent of the Indemnifying Party. The Purchaser will not
                 otherwise, without the prior written consent of the
                 Indemnifying Party (which consent shall not be unreasonably
                 withheld), settle or compromise or consent to the entry of any
                 judgment with respect to any pending or threatened Claim or
                 Proceeding, but, if such Claim or Proceeding is settled or
                 compromised or if there is entered any judgment with respect
                 to any such Claim or Proceeding, in either case with the
                 consent of the Indemnifying Party, or if there be a final
                 judgment of the plaintiff in any such Claim or Proceeding, the
                 Indemnifying Party agrees to indemnify and hold harmless the
                 Purchaser from and against any loss or liability by reason of
                 such settlement, compromise or judgment.

7.4      REFUND OF AMOUNTS

         If any person becomes entitled to a refund (whether by payment,
         credit, offset or otherwise) of all or a portion of any amount
         relating to a Claim or Proceeding for which an Indemnifying Party has,
         by payment, indemnified the Purchaser, then an amount equal to the
         refund, together with any interest received on such refund (net of any
         Tax payable on such interest), shall be paid by the Purchaser to the
         Indemnifying Party promptly after receipt of payment of the refund or
         notice from the relevant governmental authority of such credit, offset
         or other refund mechanism, as the case may be.

7.5      LIMITATION OF INDEMNITY

         The joint and several indemnity of the Vendors in respect of any
         Purchaser Tax Cost shall be limited to the proportion of such
         Purchaser Tax Cost that the number of New Exchangeable Shares issued
         hereunder is to the total number of New Exchangeable Shares issued
         pursuant to this Agreement and the similar agreement entered into as
         of the date hereof with Trimac Corporation and 761795 Alberta Ltd.
         Notwithstanding anything contained in this Article 7, the joint and
         several indemnity of the Vendors in respect of any Purchaser Tax Cost
         arising under any legislation or regulation of a jurisdiction other
         than Canada or a province or territory thereof, shall not exceed the
         sum of $1,887,243 United States dollars.


<PAGE>   15
                                     - 15 -


                                   ARTICLE 8

                                    EXPENSES

8.1      The Vendors jointly and severally agree to reimburse the Purchaser for
         all out of pocket expenses incurred by the Purchaser (including fees
         and disbursements of counsel and all tax advisors) in connection with
         the transaction contemplated herein including without limitation in
         connection with the preparation, execution and performance of this
         Agreement within 10 business days after receipt of a written invoice
         with respect thereto.  In respect of expenses which relate to this
         Agreement and to other similar agreements entered into with respect to
         other holders of Exchangeable Shares, the Vendors shall reimburse
         Purchaser in the proportion which the number of New Exchangeable
         Shares issued hereunder is to the total number of New Exchangeable
         Shares issued pursuant to all such similar agreements.

                                   ARTICLE 9

                                    CLOSING

9.1      Closing shall take place at the Closing Time on the Closing Date at
         the offices of MacKimmie Matthews, 700, 401 - 9th Avenue S.W.,
         Calgary, Alberta, or at such other place as the parties hereto may
         agree upon.

9.2      At Closing, the Vendors shall deliver to the Purchaser:

         (a)     a certified copy of the resolution of the directors of Newco
                 approving the transfer of the Newco Shares;

         (b)     certificates for the Newco Shares duly endorsed in blank for
                 transfer;

         (c)     Newco promissory note evidencing the Newco Debt endorsed for
                 payment to the Purchaser;

         (d)     written resignations from all directors and officers of Newco;
                 and

         (e)     a certificate, dated as of the Closing Date, executed by each
                 of the Vendors, to the effect that the representations and
                 warranties made in Section 4.1 are true and correct in all
                 material respects at and as of the Closing Date and that
                 Vendors have complied with all Agreements herein required to
                 be complied with at and as of the Closing Date.
<PAGE>   16
                                     - 16 -



9.3      At the Closing Time on the Closing Date, the Purchaser shall deliver
         to the Vendors certificates representing the New Exchangeable Shares.

                                   ARTICLE 10

                               CLOSING CONDITIONS

10.1     The obligation of the Purchaser to complete the purchase of the Newco
         Shares is subject to the conditions precedent that:

         (a)     the Vendors shall have performed or complied in all material
                 respects with each of the terms, covenants and conditions of
                 this Agreement to be performed or complied with by the Vendors
                 at or prior to the Closing Date:

         (b)     the approval of the Toronto Stock Exchange and all other
                 necessary regulatory approvals for the completion of the
                 transaction shall have been obtained; and

         (c)     the registration statement on Form S-3 registering the shares
                 of Pioneer Common Stock underlying the New Exchangeable Shares
                 shall have been declared effective by the United States
                 Securities and Exchange Commission.

         The condition in the Section 10.1 are for the sole benefit of the
         Purchaser and may be waived, in whole or in part, by written notice to
         the Vendors.

10.2     The obligation of the Vendors to complete the sale of the Newco Shares
         is subject to the condition precedent that the Purchaser shall have
         performed or complied in all material respects with each of the terms,
         covenants and conditions of this Agreement to be performed or complied
         with by Purchaser at or prior to the Closing Date, which condition is
         for the sole benefit of the Vendors and may be waived, in whole or in
         part, by written notice to the Purchaser.

10.3     Purchaser shall cause its counsel to apply for all required regulatory
         approvals.
<PAGE>   17
                                     - 17 -



                                   ARTICLE 11

                                 MISCELLANEOUS

11.1     This Agreement shall enure to the benefit of and be binding upon the
         parties hereto and their respective successors and permitted assigns.

11.2     All obligations of the Vendors hereunder shall be joint and several.

11.3     Any direction, notice, request, delivery or demand hereunder shall be
         in writing, shall be hand delivered or telecopied and shall be deemed
         to have been received on the date of delivery. Either party may change
         its address by notice given in the manner aforesaid.

         (a)     if to the Purchaser, addressed to:

                 Pioneer Natural Resources (Canada) Ltd.
                 c/o Pioneer Natural Resources Company
                 1400 Williams Square West
                 5205 - N O'Connor Blvd.
                 Irving, Texas
                 75039-3746
                 Attention:  General Counsel

         (b)     if to 398215, addressed to:

                 c/o Fort Chicago Energy Partners L.P.
                 Suite 975, McDougall Place
                 808 - 4th Avenue S.W.
                 Calgary, Alberta  T2P 3E8
                 Attention:  Guy J. Turcotte

         (c)     if to Turcotte

                 c/o Fort Chicago Energy Partners L.P.
                 Suite 275, McDougall Place
                 808 - 4th Avenue S.W.
                 Calgary, Alberta  T2P 3E8
                 Attention:  Guy J. Turcotte

11.4     Time shall be of the essence.

11.5     No amendment or variation of this Agreement shall be of any force or
         effect unless the same be reduced to writing and duly executed by all
         parties hereto.
<PAGE>   18
                                     - 18 -



11.6     Each of the parties shall at any time, and from time to time
         hereafter, take any and all steps, and execute, acknowledge and
         deliver to the other party, any and all further instruments and
         assurances that the other party may reasonably require for the purpose
         of giving full force and effect to the provisions of this Agreement.

11.7     Neither party may assign in whole or in part any of its interest,
         rights or obligations hereunder without the prior written agreement of
         the other party hereto except as expressly provided herein.

11.8     This Agreement may be executed in counterparts, each of which when so
         executed shall be deemed to be an original, and such counterparts
         together shall constitute one and the same instrument, which shall be
         sufficiently evidenced by such original counterparts.
<PAGE>   19
                                     - 19 -


EXECUTED AND DELIVERED.
                                   PIONEER NATURAL RESOURCES (CANADA) LTD.
                                   
                                   By:                                       
                                          -----------------------------------
                                   
                                   398215 ALBERTA LTD.
                                   
                                   By:                                       
                                          -----------------------------------
                                   
                                   GUY J. TURCOTTE
                                   
                                   By:                                       
                                          -----------------------------------
<PAGE>   20
                                   SCHEDULE A





<PAGE>   21
                                   SCHEDULE B





<PAGE>   22
                                   SCHEDULE C






<PAGE>   1
                                                                    EXHIBIT 23.1

                        CONSENT OF KPMG PEAT MARWICK LLP


The Board of Directors and Stockholders
Pioneer Natural Resources Company

We consent to the use of our reports incorporated herein by reference and to
the reference to our firm under the heading "Experts" in the registration
statement. Our reports refer to a change in the method of accounting for the
impairment of long-lived assets and for long-lived assets to be disposed of and
a change in the method of accounting for income taxes.



                                        /s/ KPMG PEAT MARWICK LLP

                                        KPMG PEAT MARWICK LLP


Midland, Texas
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.2

                   CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent public accountants, we hereby consent to the use of our reports
and to all references to our Firm included in or made a part of this
Registration Statement.


                                                         /s/ Arthur Andersen LLP

                                                             Arthur Andersen LLP



Dallas, Texas
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.3
                       CONSENT OF INDEPENDENT ACCOUNTANTS

We consent to the incorporation by reference in this Form S-3 registration
statement of Pioneer Natural Resources Company of our report dated February 14,
1997 except for Notes 12(b) and (c) which are as of September 3, 1997 and
October 29, 1997, respectively, on our audit of the consolidated financial
statements of Chauvco Resources Ltd. as at December 31, 1996 and 1995 and for
each of the years in the three year period ended December 31, 1996, and to all
references to our firm included in or made a part of this registration
statement.

                                             /s/ Price Waterhouse
                                             Chartered Accountants

Calgary, Alberta
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.4


                       CONSENT OF INDEPENDENT ACCOUNTANTS




We consent to the incorporation by reference in this Form S-3 registration
statement of Pioneer Natural Resources Company of our report dated July 26,
1996, on our audit of the financial statements of Greenhill Petroleum
Corporation as of June 30, 1996, and for the year ended. We also consent to 
the reference to our firm under the caption "Experts" in the registration 
statement.

                                                                                
                                                   /s/ Coopers & Lybrand L.L.P.

                                                   Coopers & Lybrand L.L.P.



Houston, Texas
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.5



           CONSENT OF INDEPENDENT PETROLEUM ENGINEERS AND GEOLOGISTS

         We hereby consent to the use of our audit letter prepared for Parker & 
Parsley Petroleum Company, effective December 31, 1996, and to all references
to our firm included in or made a part of this Registration Statement on Form
S-3 of Pioneer Natural Resources Company.

                                           NETHERLAND, SEWELL & ASSOCIATES, INC.



                                           By:  /s/ Frederic D. Sewell
                                                --------------------------
                                                Frederic D. Sewell
                                                President

Dallas, Texas
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.6

                CONSENT OF INDEPENDENT ENGINEERS AND GEOLOGISTS


Williamson Petroleum Consultants, Inc. (Williamson) hereby consents to the
incorporation by reference to our report entitled "Evaluation and Review of Oil
and Gas Reserves to the Interests of Mesa Inc. in the Hugoton Area, Various
Counties, Kansas and West Panhandle Area, Various Counties, Texas, Effective
December 31, 1996, for Disclosure to the Securities and Exchange Commission,
Williamson Project 6.8421" dated March 17, 1997, with respect to Mesa Inc. and
to all references to our firm included in or made a part of the Pioneer Natural
Resources Company Registration Statement on Form S-3 to be filed on February 12,
1998.




                                      /s/ Williamson Petroleum Consultants, Inc.
                                      ------------------------------------------
                                          WILLIAMSON PETROLEUM CONSULTANTS, INC.

Houston, Texas
February 12, 1998

<PAGE>   1
                                                                    EXHIBIT 23.7




                      [MILLER AND LENTS, LTD. LETTERHEAD]


                               February 12, 1998

Pioneer Natural Resources Company
1400 Williams Square West
5205 N. O'Connor Blvd.
Irving, Texas 75039-3746

                           Re:  Consent of Independent Petroleum Engineers
                                and Geologists

Gentlemen:

     We hereby consent to the incorporation by reference of our report dated
February 24, 1997 entitled "Reserve and Net Revenue Forecast as of December 31,
1996, SEC Price Case" with respect to Greenhill Petroleum Corporation and MESA
Inc. and to all references to our firm included in or made a part of the
Registration Statement on Form S-3 of Pioneer Natural Resources Company.

                                                Very truly yours,
                                                  
                                                MILLER AND LENTS, LTD.



                                                By       /s/ P.G. Von Tungeln
                                                         P.G. Von Tungeln
                                                         Chairman

<PAGE>   1
                                                                EXHIBIT 23.8

              [GILBERT LAUSTSEN JUNG ASSOCIATES LTD. LETTERHEAD]


               CONSENT OF INDEPENDENT ENGINEERS AND GEOLOGISTS

We hereby consent to the incorporation by reference of our reports entitled:

    o Chauvco Resources Ltd. (Tidal Properties), Reserve Determination and
      Economic Analysis, effective January 1, 1997, dated February 14, 1997.

    o Chauvco Resources (Gabon) S.A., Remboue Field, Reserve Determination
      and Economic Analysis, effective December 31, 1996, dated February 14, 
      1997.

    o Chauvco Resources (Gabon) S.A., Remboue Field, Reserve Determination
      and Economic Analysis, effective August 1, 1997, dated August 19, 1997.

    o Chauvco Resources (Argentina) S.A., Reserve Determination and
      Economic Analysis, effective December 31, 1996, dated January 21, 1997.

and to all references to our firm included in or made a part of this
Registration Statement on Form S-3 of Pioneer Natural Resources Company.

                                        Yours very truly,

                                        GILBERT LAUSTSEN JUNG
                                        ASSOCIATES LTD.


                                  per:  /s/ Wayne Chow

                                        Wayne W. Chow, P. Eng.
                                        Vice-President

Calgary, Alberta
Dated: February 12, 1998





<PAGE>   1
                                                                   EXHIBIT 23.9


               CONSENT OF INDEPENDENT ENGINEERS AND GEOLOGISTS


        We hereby consent to the incorporation by reference of our report
entitled "Audit of Evaluation of Oil and Gas Reserves of Pioneer Natural
Resources Canada Inc." prepared for Pioneer Natural Resources Canada Inc.
dated February 8, 1997 and to all references to our firm included in or made a 
part of this Registration Statement on Form S-3 of Pioneer Natural Resources
Company.


                                        MARTIN PETROLEUM & ASSOCIATES



                                  By:   /s/ John M. Hewitt
                                        -----------------------------
                                        John M. Hewitt, M.A., P.Eng.
                                        Associate Partner


Calgary, Alberta
February 12, 1998


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