PIONEER NATURAL RESOURCES CO
S-8, 1997-10-31
CRUDE PETROLEUM & NATURAL GAS
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<PAGE>   1
   AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON OCTOBER 31, 1997
                                                 Registration No. 333-__________
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                               _________________

                                    FORM S-8
                             REGISTRATION STATEMENT
                                     UNDER
                           THE SECURITIES ACT OF 1933
                               _________________

                       PIONEER NATURAL RESOURCES COMPANY
             (Exact name of registrant as specified in its charter)

           DELAWARE                                               75-2702753
(State or other jurisdiction of                                (I.R.S. Employer
incorporation or organization)                               Identification No.)

                           1400 WILLIAMS SQUARE WEST
                         5205 NORTH O'CONNOR BOULEVARD
                              IRVING, TEXAS 75039
          (Address of principal executive offices, including zip code)
                               _________________
                         
                      PIONEER NATURAL RESOURCES USA, INC.
                           PROFIT SHARING 401(K) PLAN

                            (Full title of the plan)

                                MARK L. WITHROW
                           1400 WILLIAMS SQUARE WEST
                         5205 NORTH O'CONNOR BOULEVARD
                              IRVING, TEXAS 75039
                                 (972) 444-9001
           (Name, address and telephone number of agent for service)

                                    copy to:
                               ROBERT L. KIMBALL
                             VINSON & ELKINS L.L.P.
                           3700 TRAMMELL CROW CENTER
                                2001 ROSS AVENUE
                            DALLAS, TEXAS 75201-2975
                                 (214) 220-7700

                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
===============================================================================================================
                                                                              Proposed
     Title of securities         Amount to be           Proposed         maximum aggregate        Amount of
      to be registered            registered         maximum offering    offering price (1)   registration fee
                                                   price per unit (1)
- ---------------------------------------------------------------------------------------------------------------
 <S>                          <C>                        <C>                    <C>                  <C>
 Common Stock, $0.01 par
 value per share . . . . .    400,000 shares(2)          $39.62                  $15,848,000          $4,803
- ---------------------------------------------------------------------------------------------------------------
 Interests in the Pioneer
 Natural Resources
 Company Profit
 Sharing 401(k) Plan . . .           (3)                   (4)                  (4)                  (4)
- ---------------------------------------------------------------------------------------------------------------
</TABLE>

(1)      Estimated solely for purposes of calculating the registration fee in
         accordance with Rule 457(h) under the Securities Act of 1933 (the
         "Securities Act") and based on the average of the high and low prices
         of the Common Stock reported on The New York Stock Exchange on October
         28, 1997.

(2)      If, as a result of stock splits, stock dividends or similar
         transactions, the number of securities purported to be registered on
         this Registration Statement changes, the provisions of Rule 416 shall
         apply to this Registration Statement, and this Registration Statement
         shall be deemed to cover the additional securities resulting from the
         split of, or the dividend on, the securities covered by this
         Registration Statement.

(3)      Pursuant to Rule 416(c) under the Securities Act, this Registration
         Statement also covers an indeterminate amount of plan interest to be
         offered or sold pursuant to the Pioneer Natural Resources USA, INC.
         Profit Sharing 401(k) Plan.

(4)      Pursuant to Rule 457(h)(2) under the Securities Act, no separate fee
         is required to register plan interests.


================================================================================

<PAGE>   2


                                   PART II
             INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents have been filed with the Securities and
Exchange Commission by Pioneer Natural Resources Company, a Delaware
corporation (the "Company"), and are incorporated herein by reference and made
a part hereof:

         (a)     The Company's Registration Statement on Form S-4 (File No.
                 333-26951) filed on June 26, 1997;

         (b)     The Company's Quarterly Report on Form 10-Q for the period
                 ended June 30, 1997;

         (c)     The Company's Current Report on Form 8-K dated August 7, 1997;


         (d)     The Company's Current Report on Form 8-K dated October 2,
                 1997;

         (e)     Joint Management Information Circular and Proxy Statement of
                 Pioneer and Chauvco filed on October 1, 1997; and

         (f)     The description of the Company's Common Stock, $0.01 par value
                 per share, contained in Item 1 of the Company's Registration
                 Statement on Form 8-A filed pursuant to the Securities
                 Exchange Act of 1934 (the "Exchange Act") on August 8, 1997.

         All documents subsequently filed by the Company pursuant to Sections
13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the filing of a
post-effective amendment that indicates that all securities offered have been
sold or that deregisters all securities then remaining unsold shall also be
deemed to be incorporated by reference herein and to be a part hereof from the
dates of filing of such documents.  Any statement contained in a document
incorporated or deemed to be incorporated by reference herein shall be deemed
to be modified or superseded for purposes of this Registration Statement to the
extent that a statement contained herein or in any other subsequently filed
document which 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, except as so modified or superseded, to constitute a part
of this Registration Statement.  Upon the written or oral request of any person
to whom a copy of this Registration Statement has been delivered, the Company
will provide without charge to such person a copy of any and all documents
(excluding exhibits thereto unless such exhibits are specifically incorporated
by reference into such documents) that have been incorporated by reference into
this Registration Statement but not delivered herewith.  Requests for such
documents should be addressed to Pioneer Natural Resources Company, 1400
Williams Square West, 5205 North O'Connor Boulevard, Irving, Texas 75039,
Attention: Secretary, (972) 444-9001.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.


ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Article Twelfth of the Restated Certificate of Incorporation of the
Company provides that the Company shall indemnify its officers and directors to
the maximum extent allowed by Delaware General Corporation Law. Pursuant to
Section 145 of the Delaware General Corporation Law, the Company 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
Company, and with respect to any criminal action, so long as they had no
reasonable cause to believe their conduct was unlawful.


                                    II-1
<PAGE>   3
         With respect to suits by or in the right of the Company, however,
indemnification is generally limited to attorney's fees and other expenses and
is not available if the person is adjudged to be liable to the Company, 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 bylaw, agreement, vote of
stockholders or disinterested directors, or otherwise.  The Company 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
Company seeking indemnification of liabilities or expenses incurred, the burden
will be on the Company to prove that the indemnification would not be permitted
under the Delaware General Corporation Law.

         The preceding discussion of the Company's Restated Certificate of
Incorporation and Section 145 of the Delaware General Corporation Law is not
intended to be exhaustive and is qualified in its entirety by the Company's
Restated Certificate of Incorporation and Section 145 of the Delaware General
Corporation Law.

         The Company has entered into indemnity agreements with its directors
and officers.  Pursuant to such agreements, the Company will, to the extent
permitted by applicable law, indemnify such persons against all expenses,
judgments, fines and penalties incurred in connection with the defense or
settlement of any actions brought against them by reason of the fact that they
were directors or officers of the Company or assumed certain responsibilities
at the direction of the Company.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

         Unless otherwise indicated below as being incorporated by reference to
another filing of the Company with the Commission, each of the following
exhibits is filed herewith:

         4.1     --       Pioneer Natural Resources USA, Inc. 401(k) Plan.

         5.1     --  (a)  Opinion of Vinson & Elkins L.L.P.

                     (b)  The Company will submit the Pioneer Natural Resources
                          USA, Inc. 401(k) Plan and any amendment thereto to
                          the Internal Revenue Service ("IRS") in a timely
                          manner and will make all changes required by the IRS
                          in order to qualify the plan.

         23.1    --       Consent of KPMG Peat Marwick LLP.

         23.2    --       Consent of Arthur Andersen LLP.

         23.3    --       Consent of Coopers & Lybrand L.L.P.

         23.4    --       Consent of Vinson & Elkins L.L.P. (included in Exhibit
                          5.1)

         24.1    --       Powers of Attorney of directors and officers of
                          Pioneer Natural Resources Company (included on page
                          II-4 to this Registration Statement).

ITEM 9.  UNDERTAKINGS.

         The Company hereby undertakes:

                 (1)      to file, during any period in which offers or sales
     are being made, a post-effective amendment to this Registration Statement:

                 (i)      to include any prospectus required by section
         10(a)(3) of the Securities Act of 1933, as amended (the "Securities
         Act");

                 (ii)     to reflect in the prospectus any facts or events
         arising after the effective date of the 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 the Registration Statement; and

                 (iii)    to include any material information with respect to
         the plan of distribution not previously disclosed in the Registration
         Statement or any material change to such information in the
         Registration Statement; provided, however, that paragraphs (1)(i) and
         (1)(ii) do not apply if the information required to be included in a
         post-effective amendment by those paragraphs is contained in periodic
         reports filed by the





                                      II-2
<PAGE>   4
         Company pursuant to section 13 or section 15(d) of the Exchange Act
         that are incorporated by reference in this Registration Statement.

                 (2)      That, for the purposes 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 such securities at that time shall be
     deemed to be the initial bona fide offering thereof.

                 (3)      To remove from registration by means of a
     post-effective amendment any of the securities being registered which
     remain unsold at the termination of the offering.

                 (4)      That, for purposes of determining any liability under
     the Securities Act, each filing of the Company's annual report pursuant to
     section 13(a) or section 15(d) of the Exchange Act that is incorporated by
     reference in the Registration Statement 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.

                 (5)      Insofar as indemnification for liabilities arising
     under the Securities Act may be permitted to directors, officers and
     controlling persons of the Company pursuant to the foregoing provisions,
     or otherwise, the Company has been advised that in the opinion of the
     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 Company of expenses incurred or paid by a director, officer or
     controlling person of the Company in the successful defense of any action,
     suit or proceeding) is asserted by such director, officer or controlling
     person in connection with the securities being registered, the Company
     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 such issue.





                                      II-3
<PAGE>   5
                                   SIGNATURES

     Pursuant to the requirements of the Securities Act of 1933, as amended,
the Company certifies that it has reasonable grounds to believe that it meets
all of the requirements for filing on Form S-8 and has duly caused this
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Irving, State of Texas, on the 31st day of
October, 1997.

                                        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                                        Capacity                          Date
          ---------                                        --------                          ----
<S>                                         <C>                                         <C>
      /s/ Scott D. Sheffield                 President, Chief Executive Officer and     October 31, 1997
- ----------------------------------------                   Director                                              
          Scott D. Sheffield                     (Principal Executive Officer)            



      /s/ M. Garrett Smith                    Senior Vice President--Finance and        October 31, 1997
- ----------------------------------------             Assistant Secretary                                                    
          M. Garrett Smith                     (Principal Financial Officer and
                                                  Principal Accounting Officer)



      /s/ I. Jon Brumley                            Chairman of the Board               October 31, 1997
- ----------------------------------------                                                                 
          I. Jon Brumley


      /s/ R. Hartwell Gardner                              Director                     October 31, 1997
- ----------------------------------------                                                                 
          R. Hartwell Gardner



      /s/ John S. Herrington                               Director                     October 31, 1997
- ----------------------------------------                                                                 
          John S. Herrington


      /s/ Kenneth A. Hersh                                 Director                     October 31, 1997
- ----------------------------------------                                                                 
          Kenneth A. Hersh



      /s/ James L. Houghton                                Director                     October 31, 1997
- ----------------------------------------                                                                 
          James L. Houghton
</TABLE>





                                      II-4
<PAGE>   6

<TABLE>
<S>                                                <C>                              <C>
      /s/ Jerry P. Jones                                   Director                  October 31, 1997
 ---------------------------------------
          Jerry P. Jones
      
      
                                                           Director                                        
 ---------------------------------------
          T. Boone Pickens
      
      
      
      /s/ Richard E. Rainwater                             Director                  October 31, 1997
 ---------------------------------------
          Richard E. Rainwater
      
      
      /s/ Charles E. Ramsey, Jr.                           Director                  October 31, 1997
 ---------------------------------------
          Charles E. Ramsey, Jr.
      
      
      
      /s/ Arthur L. Smith                                  Director                  October 31, 1997
 ---------------------------------------
          Arthur L. Smith
      
      
      /s/ Philip B. Smith                                  Director                  October 31, 1997
 ---------------------------------------
          Philip B. Smith
      
      
      
      /s/ Robert L. Stillwell                              Director                  October 31, 1997
 ---------------------------------------
          Robert L. Stillwell
      
      
      /s/ Michael D. Wortley                               Director                  October 31, 1997
 ---------------------------------------
          Michael D. Wortley




PIONEER NATURAL RESOURCES USA, INC. 401(K) PLAN                                      October 31, 1997

 By:  The 401(k) Plan Committee of the Board of                                
      Directors of Pioneer Natural Resources Company


 By:  /s/  LARRY  PAULSEN 
     ----------------------------------------------
     Larry Paulsen
     Chairman of 401(k) Plan Committee


</TABLE> 


                                     II-5
<PAGE>   7
                                 EXHIBIT INDEX


<TABLE>
<CAPTION>
Exhibit                           Description of Exhibit
- -------                           ----------------------
<S>                <C>
4.1     --       Pioneer Natural Resources USA, Inc. 401(k) Plan.

5.1     --   (a) Opinion of Vinson & Elkins L.L.P.

             (b) The Company will submit the Pioneer Natural Resources USA, 
                 Inc. 401(k) Plan and any amendment thereto to IRS in a timely 
                 manner and will make all changes required by the IRS in order 
                 to qualify the plan.

23.1    --       Consent of KPMG Peat Marwick LLP.

23.2    --       Consent of Arthur Andersen LLP.

23.3    --       Consent of Coopers & Lybrand L.L.P.

23.4    --       Consent of Vinson & Elkins L.L.P. (included in Exhibit 5.1)

24.1    --       Powers of Attorney of directors and officers of Pioneer 
                 Natural Resources Company (included on page II-4 to this 
                 Registration Statement).
</TABLE>

<PAGE>   1
                                                                     EXHIBIT 4.1


                      PIONEER NATURAL RESOURCES USA, INC.

                                  401(k) PLAN

           (As Amended and Restated Effective as of October 1, 1997)





<PAGE>   2
                      PIONEER NATURAL RESOURCES USA, INC.
                                  401(k) PLAN

           (As Amended and Restated Effective as of October 1, 1997)


                               TABLE OF CONTENTS 

<TABLE>
<CAPTION>
                                                                                                                     Page
                                                                                                                     ----
<S>                       <C>                                                                                          <C>
PREAMBLE                    . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1

ARTICLE I.                DEFINITIONS AND CONSTRUCTION  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1
                          Section 1.1  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   1
                          Section 1.2  Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8

ARTICLE II.               ELIGIBILITY AND PARTICIPATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
                          Section 2.1  Eligibility  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
                          Section 2.2  Participation  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .   9

ARTICLE III.              CONTRIBUTIONS, LIMITATIONS AND FORFEITURES  . . . . . . . . . . . . . . . . . . . . . . . .   9
                          Section 3.1  Pre-Tax and Pre-Tax Bonus Contributions  . . . . . . . . . . . . . . . . . . .   9
                          Section 3.2  Payment of Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
                          Section 3.3  Return of Employer Contributions . . . . . . . . . . . . . . . . . . . . . . .  10
                          Section 3.4  Contribution Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
                          Section 3.5  Application of Forfeitures . . . . . . . . . . . . . . . . . . . . . . . . . .  13
                          Section 3.6  Rollover Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14

ARTICLE IV.               TRUST FUND  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
                          Section 4.1  Trust and Trustee  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
                          Section 4.2  Trust Investment Options . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
                          Section 4.3  Valuation and Adjustment of Accounts . . . . . . . . . . . . . . . . . . . . .  14

ARTICLE V.                VESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
                          Section 5.1  Fully Vested Accounts  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  15
                          Section 5.2  Vesting of Employer Account  . . . . . . . . . . . . . . . . . . . . . . . . .  15

ARTICLE VI.               VALUATIONS, DISTRIBUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
                          Section 6.1  Time and Form of Distribution  . . . . . . . . . . . . . . . . . . . . . . . .  16
                          Section 6.2  Distribution of Retirement and Disability
                                                   Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
                          Section 6.3  Distribution of Death Benefit  . . . . . . . . . . . . . . . . . . . . . . . .  18
</TABLE>





                                      (i)
<PAGE>   3
<TABLE>
<S>                       <C>                                                                                          <C>
                          Section 6.4  Distribution of Separation from Employment
                                                   Benefit  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  19
                          Section 6.5  Forfeitures  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
                          Section 6.6  In-Service Withdrawals . . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
                          Section 6.7  Distributions to Minors and Persons Under Legal
                                                   Disability . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
                          Section 6.8  Benefits Payable to Missing Participant or
                                                   Beneficiary  . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
                          Section 6.9  Plan Loans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  23
                          Section 6.10 Qualified Domestic Relations Orders  . . . . . . . . . . . . . . . . . . . . .  24
                          Section 6.11 Transfer of Eligible Rollover Distribution . . . . . . . . . . . . . . . . . .  25

ARTICLE VII.              PLAN ADMINISTRATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  26
                          Section 7.1  401(k) Plan Committee  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  26
                          Section 7.2  Powers, Duties and Liabilities of the Committee  . . . . . . . . . . . . . . .  26
                          Section 7.3  Rules, Records and Reports . . . . . . . . . . . . . . . . . . . . . . . . . .  26
                          Section 7.4  Administration Expenses and Taxes  . . . . . . . . . . . . . . . . . . . . . .  27

ARTICLE VIII.             AMENDMENT AND TERMINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  27
                          Section 8.1  Amendment  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  27
                          Section 8.2  Termination  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  27

ARTICLE IX.               TOP-HEAVY PROVISIONS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
                          Section 9.1  Top-Heavy Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  28
                          Section 9.2  Minimum Contribution Requirement . . . . . . . . . . . . . . . . . . . . . . .  29
                          Section 9.3  Minimum Vesting Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . .  30

ARTICLE X.                MISCELLANEOUS GENERAL PROVISIONS  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
                          Section 10.1  Spendthrift Provision . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
                          Section 10.2  Claims Procedure  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  30
                          Section 10.3  Maximum Contribution Limitation . . . . . . . . . . . . . . . . . . . . . . .  31
                          Section 10.4  Employment Noncontractual . . . . . . . . . . . . . . . . . . . . . . . . . .  31
                          Section 10.5  Limitations on Responsibility . . . . . . . . . . . . . . . . . . . . . . . .  31
                          Section 10.6  Merger or Consolidation . . . . . . . . . . . . . . . . . . . . . . . . . . .  31
                          Section 10.7  Applicable Law  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  32
</TABLE>





                                      (ii)
<PAGE>   4
                      PIONEER NATURAL RESOURCES USA, INC.
                                  401(k) PLAN

           (As Amended and Restated Effective as of October 1, 1997)

         THIS 401(k) PLAN, a profit sharing plan, made and executed by PIONEER
NATURAL RESOURCES USA, INC., a Delaware corporation (the "Company"),

                        W I T N E S S E T H   T H A T :

         WHEREAS, the Company has heretofore established a qualified profit
sharing plan known as the Pioneer Natural Resources USA, Inc. 401(k) Plan (the
"Plan") for the benefit of its employees; and

         WHEREAS, the Company has heretofore established a qualified profit
sharing plan and trust known as the Mesa Profit-Sharing Plan and Trust
Agreement, effective January 1, 1989, for the benefit of its and its
affiliates' employees; and

         WHEREAS, the Company has amended and restated the Mesa Profit-Sharing
Plan and Trust Agreement to merge with and into the Plan effective as of
October 1, 1997; and

         WHEREAS, the Company now desires to continue the Plan without
interruption by amending and restating its provisions in their entirety to
update the plan language, incorporate prior amendments and make certain other
changes;

         NOW, THEREFORE, in consideration of the premises and pursuant to
Article 14 thereof, the Company hereby amends and restates the Pioneer Natural
Resources USA, Inc. 401(k) Plan, effective as of October 1, 1997, to read as
follows:


                                   ARTICLE I.
                          DEFINITIONS AND CONSTRUCTION
         Section 1.1  Definitions.  Unless the context clearly indicates
otherwise, when used in this Plan:

                 (a)      "Account" means a Participant's Employer Account,
         Mesa Profit-Sharing Account, Pre-Tax Account, Prior Plan Employer
         Account, Prior Plan Pre-Tax Account and/or Rollover Account, as the
         context requires.  The Committee may establish and maintain separate
         subaccounts within a Participant's Accounts if it deems such to be
         necessary to the proper administration of the Plan.

                 (b)      "Affiliated Company" means any corporation or
         organization, other than an Employer, which is a member of a
         controlled group of corporations (within





<PAGE>   5
         the meaning of Section 414(b) of the Code) or of an affiliated service
         group (within the meaning of Section 414(m) of the Code) with respect
         to which an Employer is also a member, and any other incorporated or
         unincorporated trade or business which along with an Employer is under
         common control (within the meaning of the regulations from time to
         time promulgated by the Secretary of the Treasury pursuant to Section
         414(c) of the Code); provided, however, that for the purposes of
         Section 10.3 of the Plan, Section 414(b) and (c) of the Code shall be
         applied as modified by Section 415(h) of the Code.

                 (c)      "Basic Compensation" means the base salary or wages
         and any overtime payable by an Employer to an Employee for personal
         services rendered to the Employer prior to reduction for any Total
         Pre-Tax Contributions made by such Employer to this Plan on behalf of
         such Employee and prior to reduction for any compensation reduction
         amounts elected by such Employee for benefits pursuant to a cafeteria
         plan (within the meaning of Section 125(d) of the Code) maintained by
         an Employer; provided, however, that the Basic Compensation of an
         Employee taken into account under the Plan for any Plan Year shall not
         exceed $150,000 (as adjusted to take into account any cost-of-living
         increases authorized pursuant to Section 401(a)(17)(B) of the Code).

                 (d)      "Code" means the Internal Revenue Code of 1986, as 
         amended.

                 (e)      "Committee" means the 401(k) Plan Committee appointed
         by the Board of Directors of the Company to administer the Plan.

                 (f)      "Company" means Pioneer Natural Resources USA, Inc.,
         a Delaware corporation, and any successor thereto.

                 (g)      "Company Stock" means the common stock of Pioneer
         Natural Resources Company, a Delaware corporation, and any successor
         thereto.

                 (h)      "Compensation" means the sum of (i) the Limitation
         Compensation paid by an Employer to an Employee, (ii) any Total
         Pre-Tax Contributions made by an Employer to this Plan on behalf of
         such Employee, and (iii) any salary reduction amounts elected by such
         Employee for the purchase of benefits pursuant to a cafeteria plan
         (within the meaning of Section 125(d) of the Code) maintained by an
         Employer; provided, however, that except for purposes of determining
         whether an Employee is a Highly Compensated Employee or a Key Employee
         (as defined in Section 9.1(c)), the Compensation of an Employee taken
         into account under the Plan for any Plan Year shall not exceed
         $150,000 (as adjusted to take into account any cost-of-living
         increases authorized pursuant to Section 401(a)(17)(B) of the Code).
         Solely for purposes of this definition, compensation from an employer
         participating in the Mesa Profit-Sharing Plan prior to October 1,
         1997, shall be deemed to be Compensation.





                                      -2-
<PAGE>   6
                 (i)      "Covered Employee" means any Employee other than (i)
         a member of a collective bargaining unit with which an Employer
         negotiates and with respect to whom no coverage under this Plan has
         been provided by collective bargaining agreement, (ii) a nonresident
         alien with respect to the United States who receives no earned income
         from an Employer which constitutes income from sources within the
         United States, (iii) a temporary or seasonal Employee as determined in
         accordance with the Employer's normal personnel policies, (iv) an
         individual performing services for an Employer whom the Employer
         treats as an independent contractor for employment tax purposes, or
         (v) an individual who is treated as a leased employee by an Employer.

                 (j)      "Employee" means any individual employed by an
         Employer.

                 (k)      "Employer" shall include the Company and any other
         incorporated or unincorporated trade or business which may
         subsequently adopt this Plan with the consent of the Board of
         Directors of the Company.

                 (l)      "Employer Account" means the account established and
         maintained under this Plan by the Committee to record a Participant's
         interest under this Plan attributable to (i) any amounts credited to
         his or her Employer Matching Contribution Account under the Superseded
         Plan as in effect on September 30, 1997 and (ii) any amounts credited
         to his or her Employer Nonelective Contribution Account under the
         Superseded Plan as in effect on September 30, 1997.

                 (m)      "Employment Date" means the date an Employee first
         performs an Hour of Service.

                 (n)      "Highly Compensated Employee" means for a Plan Year
         commencing after December 31, 1996:

                          (1)     any Employee who during such Plan Year or
                 during the preceding Plan Year was at any time a 5-percent
                 owner (as defined in Section 416(i)(1) of the Code) of an
                 Employer or Affiliated Company; or

                          (2)     any Employee who during the preceding Plan
                 Year received Compensation greater than $80,000 (as adjusted
                 to take into account any cost-of-living increases authorized
                 pursuant to Section 414(q)(1) of the Code) and, if the Company
                 so elects, who is in the group consisting of the top 20% (when
                 ranked on the basis of Compensation received during such
                 preceding year) of all Employees, except those excluded
                 pursuant to Section 414(q)(5) of the Code.

         Solely for purposes of this definition, (i) an employee of either an
         Affiliated Company or an employer participating in the Mesa
         Profit-Sharing Plan shall be deemed to be an Employee, (ii)
         compensation received from either an Affiliated Company or an





                                      -3-
<PAGE>   7
         employer participating in the Mesa Profit-Sharing Plan shall be deemed
         to be Compensation, and (iii) a nonresident alien who receives no
         earned income from an Employer or Affiliated Company which constitutes
         income from sources within the United States shall not be considered
         an Employee.  For the Plan Year ending December 31, 1996, Highly
         Compensated Employees shall be determined pursuant to the provisions
         of the Retirement Savings Plan for Employees of Parker & Parsley as in
         effect for such Plan Year.

                 (o)      "Hour of Service" means an hour for which an Employee
         is directly or indirectly compensated or entitled to compensation
         (including back pay, regardless of mitigation of damages) by an
         Employer for the performance of duties for an Employer or for reasons
         (such as vacation, sickness or disability) other than the performance
         of duties for an Employer.  An Employee will be credited with eight
         Hours of Service per day for any customary work period during which
         such Employee is on leave of absence authorized by his or her
         Employer.  Leaves of absence shall be granted by an Employer to its
         Employees on a uniform, nondiscriminatory basis.  In no event shall
         more than 501 Hours of Service be credited on account of any single
         continuous period during which the individual performs no duties.  An
         Employee's Hours of Service shall be credited to the appropriate Plan
         Years or eligibility computation period determined in accordance with
         the provisions of Section 2530.200b-2(b) and (c) of the Department of
         Labor Regulations, which are incorporated herein by this reference.
         In determining Hours of Service for the purposes of this Plan, periods
         of employment by an Affiliated Company and periods of employment as a
         leased employee (within the meaning of Section 414(n) of the Code) of
         an Employer or Affiliated Company shall be deemed to be periods of
         employment by an Employer.

                 (p)      "Investment Fund" means any fund authorized for the
         investment of Trust assets pursuant to Section 4.2.

                 (q)      "Limitation Compensation" means wages within the
         meaning of Section 3401(a) of the Code and all other payments of
         remuneration to an Employee by an Employer (in the course of the
         Employer's trade or business) for which the Employer is required to
         furnish the Employee a written statement under Sections 6041(d),
         6051(a)(3) and 6052 of the Code, but determined without regard to any
         rules that limit the remuneration included in wages based on the
         nature or location of the employment or the services performed (such
         as the exception for agricultural labor in Section 3401(a)(2) of the
         Code); provided, however, that the Limitation Compensation of an
         Employee taken into account under the Plan for any Plan Year shall not
         exceed $150,000 (as adjusted to take into account any cost-of-living
         increases authorized pursuant to Section 401(a)(17)(B) of the Code).

                 (r)      "Mesa Profit-Sharing Account" means the account
         established and maintained under this Plan by the Committee to record
         a Participant's interest under





                                      -4-
<PAGE>   8
         this Plan attributable to his or her accrued benefit derived from
         employer contributions to the Mesa Profit- Sharing Plan as in effect
         on September 30, 1997.

                 (s)      "Mesa Profit-Sharing Plan" means the Mesa
         Profit-Sharing Plan and Trust Agreement as in effect from time to time
         prior to October 1, 1997.

                 (t)      "Non-Highly Compensated Employee" means for a Plan
         Year any Employee who is not a Highly Compensated Employee for such
         Plan Year.

                 (u)      The "Normal Retirement Date" of a Participant means
         the day such Participant attains the age of 65 years.

                 (v)      "One Year Break in Service" means a 12 consecutive
         month Period of Severance during which an Employee fails to complete a
         single Hour of Service.

                 (w)      "Participant" means any individual who was a
         participant in either the Superseded Plan or the Mesa Profit-Sharing
         Plan or who has elected to participate in this Plan pursuant to
         Section 2.2, and whose Vested Interest under this Plan has not been
         fully distributed.

                 (x)      "Period of Service" means, for purposes of
         determining a Participant's Vested Interest in his or her Employer
         Account, the sum, rounded downward to the nearest whole year, of each
         period of time commencing with an Employee's Employment Date or
         Reemployment Date and ending on the first date thereafter a Period of
         Severance begins (except as provided in subsection (y) of this Section
         in the case of an Employee's maternity or paternity leave of absence).
         Included in such sum to be credited to an Employee shall be each
         period of time during which the Employee is on an authorized leave of
         absence for reasons of vacation, sickness, layoff or another occasion
         designated and applied by an Employer or Affiliated Company on a
         nondiscriminatory basis, but in no event exceeding one year in length.
         A Period of Service also includes any Period of Severance of less than
         12 consecutive months.  If an Employee who has no vested right to any
         amount credited to his or her Employer Account incurs a One Year Break
         in Service, such Employee shall forfeit his or her prior Period of
         Service unless he or she completes an additional one-year Period of
         Service before the number of his or her consecutive One Year Breaks in
         Service equals five.

                 Any provision of this Plan to the contrary notwithstanding, if
         a Participant participated in the Superseded Plan prior to October 1,
         1997, the Period of Service completed by such Participant prior to
         January 1, 1998, shall be (i) such Participant's years of Vesting
         Service determined under the Retirement Savings Plan for Employees of
         Parker & Parsley as of June 27, 1996, (ii) plus one year for the Plan
         Year ending December 31, 1996, if during such Plan Year such
         Participant completed a Year of Service under the Retirement Savings
         Plan for Employees of Parker & Parsley as in effect at the end of such
         year, (iii) plus one year for the Plan Year





                                      -5-
<PAGE>   9
         ending December 31, 1997, if such Participant either (A) completed a
         year of Vesting Service as of September 30, 1997, under the Superseded
         Plan as in effect on such date or (B) completed a one-year Period of
         Service under the foregoing provisions of this definition during the
         entire such Plan Year.  For purposes of clause (ii) of the preceding
         sentence, a Participant shall be credited with a number of Hours of
         Service applying the monthly equivalency method set forth in Labor
         Reg. Section  2530.200b-3(e)(1)(iv) to any fractional part of a year
         credited to such Participant as of June 28, 1996.

                 (y)      "Period of Severance" means a period of time
         commencing with the date an Employee ceases to be employed by an
         Employer or Affiliated Company for reasons of Retirement, Permanent
         Disability, death, being discharged, or voluntarily ceasing
         employment, or with the first anniversary of the date of his or her
         absence for any other reason, and ending with the date such Employee
         resumes employment with an Employer or Affiliated Company; provided,
         however, that solely for purposes of determining whether an Employee
         incurs a One Year Break in Service, the Period of Severance of an
         Employee who is absent from work due to the pregnancy of the Employee,
         the birth of a child of the Employee, the placement of a child with
         the Employee in connection with the adoption of such child by such
         Employee, or caring for such child for a period beginning immediately
         following such birth or placement shall not commence until the second
         anniversary of the first date of such absence and the period between
         the first and second anniversaries of the first date of such absence
         shall be considered neither a Period of Service nor a Period of
         Severance.

                 (z)      "Permanent Disability" means the total and permanent
         incapacity of a Participant to perform the usual duties of his or her
         employment with an Employer or Affiliated Company as determined by the
         Committee.  Such incapacity shall be deemed to exist when certified by
         a physician acceptable to the Committee.

                 (aa)     "Pioneer Matching Plan" means the Pioneer Natural
         Resources USA, Inc. Matching Plan, amended and restated effective as
         of October 1, 1997, and as from time to time in effect thereafter.

                 (bb)     "Plan" means this Pioneer Natural Resources USA, Inc.
         401(k) Plan, amended and restated effective as of October 1, 1997, and
         as from time to time in effect thereafter.

                 (cc)     "Plan Year" means the calendar year.

                 (dd)     "Pre-Tax Account" means the account established and
         maintained under this Plan by the Committee to record a Participant's
         interest under this Plan attributable to Pre-Tax Contributions and
         Pre-Tax Bonus Contributions made by an Employer on behalf of such
         Participant and any amounts credited to his or her Employee Pre-Tax
         Contribution Account under the Superseded Plan as in effect on
         September 30, 1997.





                                      -6-
<PAGE>   10
                 (ee)     "Pre-Tax Bonus Contribution" means (i) an Employee
         Pre-Tax Bonus Contribution made on behalf of a Participant to the
         Superseded Plan after June 27, 1996, and prior to October 1, 1997, and
         (ii) a contribution made by an Employer to this Plan on behalf of a
         Participant pursuant to Section 3.1(b).

                 (ff)     "Pre-Tax Contribution" means (i) a Salary Deferral
         Contribution made on behalf of a Participant to the Superseded Plan
         prior to June 28, 1996, (ii) an Employee Pre-Tax Contribution made on
         behalf of a Participant to the Superseded Plan after June 27, 1996,
         and prior to October 1, 1997, and (iii) a contribution made by an
         Employer to this Plan on behalf of a Participant pursuant to Section
         3.1(a).

                 (gg)     "Prior Plan Employer Account" means the account
         established and maintained under this Plan by the Committee to record
         a Participant's interest under this Plan attributable to any amounts
         credited to his or her BOUSA Employer Matching Contribution Account
         under the Retirement Savings Plan for Employees of Parker & Parsley as
         in effect on June 27, 1996.

                 (hh)     "Prior Plan Pre-Tax Account" means the account
         established and maintained under this Plan by the Committee to record
         a Participant's interest under this Plan attributable to any amounts
         credited to his or her Plan A Salary Deferral Contribution Account or
         his or her BOUSA Plan Salary Deferral Contribution Account under the
         Retirement Savings Plan for Employees of Parker & Parsley as in effect
         on June 27, 1996.

                 (ii)     "Qualified Joint and Survivor Annuity" means an
         annuity which is payable for the life of the Participant with a
         survivor annuity payable for the life of his or her spouse equal to
         50% of the amount of the annuity payable during the life of the
         Participant; provided, however, that in the case of a Participant who
         is not married, a Qualified Joint and Survivor Annuity means an
         annuity which is payable for the life of the Participant.

                 (jj)     "Qualified Preretirement Survivor Annuity" means an
         annuity which is payable for the life of the Participant's surviving
         spouse.

                 (kk)     "Reemployment Date" means the date an Employee first
         performs an Hour of Service following a Period of Severance.

                 (ll)     "Retirement" means the termination of a Participant's
         employment with an Employer or Affiliated Company on or after his or
         her Normal Retirement Date for any reason other than death or transfer
         to the employment of another Employer or Affiliated Company.

                 (mm)     "Rollover Account" means the account established and
         maintained under this Plan by the Committee to record a Participant's
         interest under this Plan attributable to (i) Rollover Property
         contributed by such Participant to this Plan





                                      -7-
<PAGE>   11
         pursuant to Section 3.6, (ii) any amounts credited to his or her
         Rollover Contribution Account under the Superseded Plan as in effect
         on September 30, 1997, and (iii) any amounts credited to his or her
         Rollover Account under the Mesa Profit-Sharing Plan as in effect on
         September 30, 1997.

                 (nn)     "Rollover Property" means property the value of which
         would be excluded from the gross income of the transferor under
         Section 402(c), 403(a)(4) or 408(d)(3) of the Code if transferred to
         the Plan.

                 (oo)     "Superseded Plan" means the Pioneer Natural Resources
         USA, Inc. 401(k) Plan (formerly known as the Retirement Savings Plan
         for Employees of Parker & Parsley), as in effect from time to time
         prior to October 1, 1997.

                 (pp)     "Total Pre-Tax Contributions" means the sum of the
         Pre-Tax Contributions and Pre-Tax Bonus Contributions made on behalf
         of a Participant.

                 (qq)     "Trust" means the trust fund established pursuant to 
         Section 4.1.

                 (rr)     "Trustee" means the individual or corporate trustee
         or trustees from time to time appointed and acting as trustee or
         trustees of the Trust established pursuant to the Plan.

                 (ss)     "Valuation Date" means each business day.

                 (tt)     The "Vested Interest" of a Participant means the then
         vested portion of the amount credited to the Accounts of such
         Participant at the particular point in time in question.

         Section 1.2  Construction.  The titles to the Articles and the
headings of the Sections in this Plan are placed herein for convenience of
reference only and in case of any conflict the text of this instrument, rather
than such titles or headings, shall control.  Whenever a noun or pronoun is
used in this Plan in plural form and there be only one person or entity within
the scope of the word so used, or in singular form and there be more than one
person or entity within the scope of the word so used, such noun or pronoun
shall have a plural or singular meaning as appropriate under the circumstance.


                                  ARTICLE II.

                         ELIGIBILITY AND PARTICIPATION

         Section 2.1  Eligibility.  Each Covered Employee who is a participant
in either the Superseded Plan or the Mesa Profit-Sharing Plan on September 30,
1997, shall continue to be eligible to participate in this Plan as of October
1, 1997.  Each other Covered Employee shall be eligible to participate in this
Plan on the first day of the first pay period in the





                                      -8-
<PAGE>   12
calendar month next following his or her employment as a Covered Employee.  If
a Participant ceases to be a Covered Employee, such Participant shall remain a
Participant under this Plan but no contributions shall be made to the Plan on
his or her behalf while he or she is not a Covered Employee.

         Section 2.2  Participation.  Each Covered Employee who is eligible to
participate in the Plan may elect, on a form prescribed by the Committee, to
participate in this Plan on the first day of the first pay period in the
calendar month following the filing of such election.  Any Participant who
ceases to be a Covered Employee shall thereupon cease to participate in the
Plan; provided, however, that if any such Participant is thereafter reemployed
as a Covered Employee, he or she shall be eligible to elect to resume
participating in the Plan as of the date of such reemployment.


                                  ARTICLE III.

                   CONTRIBUTIONS, LIMITATIONS AND FORFEITURES

         Section 3.1  Pre-Tax and Pre-Tax Bonus Contributions.

                 (a)      Each Participant may elect to have his or her
         Employer make a Pre-Tax Contribution to the Plan on his or her behalf
         for each pay period in an amount equal to a whole percentage, of at
         least 2% and not in excess of 12%, of his or her Basic Compensation
         for that pay period.  All such contributions shall be made by uniform
         payroll deductions pursuant to a Basic Compensation reduction
         agreement which authorizes the Employer to pay such contributions to
         the Trustee on behalf of the Participant.

                 (b)      In addition, each Participant may elect pursuant to a
         separate bonus reduction agreement to have his or her Employer make a
         Pre-Tax Bonus Contribution to the Plan on his or her behalf in an
         amount equal to a whole percentage, of at least 2% and not in excess
         of 12%, of any cash bonus payable under the Company's Annual Incentive
         Bonus Program to such Participant.

                 (c)      The Committee shall establish and maintain for each
         Participant a Pre-Tax Account.  All amounts attributable to Pre-Tax
         Contributions and Pre-Tax Bonus Contributions made by an Employer on
         behalf of such Participant pursuant to this Section 3.1 shall be
         credited to such Participant's Pre-Tax Account.

                 (d)      A Participant may change the applicable percentage of
         such payroll (or bonus) deductions as of the first day of the first
         pay period of any calendar quarter, or at any time suspend his or her
         election to have Pre-Tax Contributions and/or Pre-Tax Bonus
         Contributions made to the Plan, provided that written notice of such
         change or suspension is delivered to the Committee within such
         reasonable period of time prior to the effective date thereof as the
         Committee may require.  If a Participant suspends





                                      -9-
<PAGE>   13
         his or her election to have Pre-Tax Contributions and/or Pre-Tax Bonus
         Contributions made to the Plan, such Participant shall be eligible to
         reelect to have such contributions made to the Plan as of the first
         day of the month coinciding with or following the expiration of three
         months after the effective date of such suspension.

                 (e)      Any provision of this Plan to the contrary
         notwithstanding, the amount of Total Pre-Tax Contributions made to the
         Plan pursuant to this Section 3.1 on behalf of a Participant shall not
         exceed $7,000 (as adjusted to take into account any cost-of-living
         increases authorized pursuant to Section 402(g) of the Code) for any
         calendar year.

                 (f)  An Employer may amend or revoke any Participant's Basic
         Compensation reduction agreement or bonus reduction agreement at any
         time during a Plan Year if such amendment or revocation is deemed by
         such Employer to be necessary or appropriate to ensure that the
         requirements of Sections 3.1(e), 3.4 and 10.3 are met for such year.

         Section 3.2  Payment of Contributions.  The Pre-Tax Contributions and
Pre-Tax Bonus Contributions made to the Plan by an Employer for a pay period
shall be paid to the Trustee in cash as soon as practicable after the end of
the month in which such pay period ends, but no later than the 15th business
day after the end of such month.

         Section 3.3  Return of Employer Contributions.  Contributions made to
this Plan are conditioned upon being currently deductible under Section 404 of
the Code.  Any provision of this Plan to the contrary notwithstanding, upon an
Employer's request, any such contribution or portion thereof made to this Plan
by such Employer which (i) was made under a mistake of fact which is
subsequently discovered, or (ii) is disallowed as a deduction under Section 404
of the Code, shall be returned to such Employer to the extent not previously
distributed to Participants or their beneficiaries; provided, however, that the
amounts returnable to an Employer pursuant to this Section shall be reduced by
any Trust losses allocable thereto and shall be returned to such Employer only
if such return is made within one year after the mistaken payment of the
contribution or the date of the disallowance of the deduction, as the case may
be.  Except as provided in this Section, no contribution made by an Employer
pursuant to this Plan shall ever revert to or be recoverable by any Employer.

         Section 3.4  Contribution Limitations.

                 (a)      Any provision of this Plan to the contrary
         notwithstanding, if for any Plan Year the actual deferral percentage
         for the group of Highly Compensated Employees eligible to elect to
         have Pre-Tax Contributions or Pre-Tax Bonus Contributions made during
         such Plan Year fails to satisfy one of the following tests:

                          (1)     the actual deferral percentage for said group
                 of Highly Compensated Employees is not more than 1.25 times
                 the actual deferral





                                      -10-
<PAGE>   14
                 percentage for the preceding Plan Year for all Non-Highly
                 Compensated Employees eligible during the preceding Plan Year
                 to elect to have Pre-Tax Contributions or Pre-Tax Bonus
                 Contributions made on their behalf, or

                          (2)     the excess of the actual deferral percentage
                 for said group of Highly Compensated Employees over the actual
                 deferral percentage for the preceding Plan Year for all
                 Non-Highly Compensated Employees eligible during the preceding
                 Plan Year to elect to have Pre-Tax Contributions or Pre-Tax
                 Bonus Contributions made on their behalf is not more than two
                 percentage points, and the actual deferral percentage for said
                 group of Highly Compensated Employees is not more than two
                 times the actual deferral percentage for the preceding year
                 for all Non-Highly Compensated Employees eligible during the
                 preceding Plan Year to elect to have Pre-Tax Contributions or
                 Pre-Tax Bonus Contributions made on their behalf,

         then the actual deferral percentage of Participants who are members of
         said group of Highly Compensated Employees shall be reduced by
         reducing the Total Pre-Tax Contributions made for such Plan Year on
         behalf of the Highly Compensated Employees with the largest individual
         actual deferral percentages to the largest uniform actual deferral
         percentage (commencing with the Highly Compensated Employee with the
         largest actual deferral percentage and reducing his or her actual
         deferral percentage to the extent necessary to satisfy one of the
         above tests or to lower such actual deferral percentage to the actual
         deferral percentage of the Highly Compensated Employee with the next
         highest actual deferral percentage, and repeating this process as
         necessary) that permits the actual deferral percentage for said group
         of Highly Compensated Employees to satisfy one of said tests.  For
         purposes of this subsection (a), the term "actual deferral percentage"
         for a specified group of Employees for a Plan Year means the average
         of the ratios (calculated separately for each Employee in such group
         and after any distributions to Highly Compensated Employees required
         to satisfy the adjusted $7,000 limitation described in Section 3.1(e))
         of (i) the aggregate amount of Total Pre-Tax Contributions made to the
         Plan on behalf of each such Employee for that year and, if elected by
         the Committee, an amount of Matching Contributions made for such
         Employee pursuant to the Pioneer Matching Plan not in excess of the
         amount of such contributions permitted to be taken into account under
         Sections 401(k) and (m) of the Code and the regulations thereunder, to
         (ii) the amount of such Employee's Compensation for that year or, in
         the Committee's discretion, only for such portion of that year during
         which the Employee was eligible to participate in the Plan.  Any
         provision of this Section to the contrary notwithstanding, for the
         Plan Year ending December 31, 1997, the Company may elect, in
         accordance with Section 401(k) of the Code and other applicable
         authority, to use data for the current Plan Year rather than the
         preceding Plan Year in computing the actual deferral percentage of
         Non-Highly Compensated Employees.  If two or more plans that include
         cash or deferred arrangements are considered as one plan for purposes
         of Section 401(a)(4) or 410(b) of the Code (other than for purposes of
         the average benefit percentage test), the cash or deferred
         arrangements included in





                                      -11-
<PAGE>   15
         such plans shall be treated as one arrangement for purposes of this
         subsection (a).  If a Highly Compensated Employee is a participant in
         two or more cash or deferred arrangements of an Employer, then for
         purposes of determining the actual deferral ratio of such Employee,
         all such cash or deferred arrangements (other than those that may not
         be permissively aggregated) shall be treated as one cash or deferred
         arrangement.

                 (b)      The aggregate amount of any Total Pre-Tax
         Contributions made on behalf of Participants which cannot be credited
         to the Pre-Tax Accounts for a Plan Year because of the limitation
         contained in subsection (a) of this Section (along with any income
         allocable to such contributions for such Plan Year, but not for the
         gap period following such Plan Year) shall be distributed to such
         Participants no later than 2 1/2 months after the end of such year on
         the basis of the amount of Total Pre-Tax Contributions made for each
         such Participant (commencing with the Highly Compensated Employee with
         the largest amount of Total Pre-Tax Contributions for such Plan Year
         and reducing his or her Total Pre-Tax Contributions to the extent
         necessary or to lower such amount to the amount of Total Pre-Tax
         Contributions of the Highly Compensated Employee with the next highest
         amount of Total Pre-Tax Contributions, and repeating this process as
         necessary).  Any such excess contributions distributed to a
         Participant shall be distributed first from any Pre-Tax Bonus
         Contributions and then, to the extent necessary, from Pre-Tax
         Contributions.  The income allocable to any such excess contributions
         for a Participant for a Plan Year shall be determined by multiplying
         the amount of income allocable to such Participant's Pre-Tax Account
         for such year by a fraction, the numerator of which is the amount of
         the excess contributions for such year and the denominator of which is
         the sum of the amount credited to such Participant's Pre-Tax Account
         as of the beginning of such year plus the amount of such Participant's
         Total Pre-Tax Contributions for such year.

                 (c)      The preceding provisions of this Section 3.4 to the
         contrary notwithstanding, in lieu of distributing contributions which
         would otherwise be allocated to a Participant's Accounts on account of
         the limitations provided in the preceding provisions of this Section,
         the Company in its absolute discretion may direct the Employers to
         make qualified nonelective employer contributions to the Plan to be
         allocated to the Pre-Tax Accounts of Non-Highly Compensated Employees
         in a manner which complies with Sections 401(a)(4) and 401(k) of the
         Code and the regulations thereunder.

                 (d)      Any provision of this Plan to the contrary
         notwithstanding, in addition to the above limitations of this Section,
         the sum of the actual deferral percentage and the contribution
         percentage for the group of Highly Compensated Employees as determined
         pursuant to and after any reduction in such percentages required by
         subsection (a) of this Section and Section 3.6(a) of the Pioneer
         Matching Plan shall not exceed the "aggregate limit."  The "aggregate
         limit" shall be equal to the greater of:





                                      -12-
<PAGE>   16
                          (1)  the sum of: (i) 1.25 times the greater of the
                 relevant actual deferral percentage or the relevant
                 contribution percentage, and (ii) two percentage points plus
                 the lesser of the relevant actual deferral percentage or the
                 relevant contribution percentage, provided that the amount in
                 this clause (ii) shall not exceed two times the lesser of the
                 relevant actual deferral percentage or the relevant
                 contribution percentage; or

                          (2)  the sum of: (i) 1.25 times the lesser of the
                 relevant actual deferral percentage or the relevant
                 contribution percentage, and (ii) two percentage points plus
                 the greater of the relevant actual deferral percentage or the
                 relevant contribution percentage, provided that the amount in
                 this clause (ii) shall not exceed two times the greater of the
                 relevant actual deferral percentage or the relevant
                 contribution percentage.

         The "relevant actual deferral percentage" means the actual deferral
         percentage determined for the preceding Plan Year pursuant to
         subsection (a) of this Section for the group of Non-Highly Compensated
         Employees eligible during the preceding Plan Year to have Pre-Tax
         Contributions or Pre-Tax Bonus Contributions made.  The "relevant
         contribution percentage" means the contribution percentage determined
         for the preceding Plan Year pursuant to Section 3.6(a) of the Pioneer
         Matching Plan for the group of Non-Highly Compensated Employees
         eligible for the preceding Plan Year to receive an allocation of
         Matching Contributions.  In the event that the aggregate limit is
         exceeded in any year, then the actual deferral percentage and/or
         contribution percentage under the Pioneer Matching Plan for
         Participants who are members of the group of Highly Compensated
         Employees shall be reduced by reducing Total Pre-Tax Contributions
         and/or Matching Contributions made for such Plan Year for or on behalf
         of the Highly Compensated Employees with the largest individual actual
         deferral percentages and/or contribution percentages to the largest
         uniform actual deferral percentage and/or contribution percentage
         (proceeding in the manner prescribed in subsection (a) of this Section
         and Section 3.6(a) of the Pioneer Matching Plan) that permits the sum
         of the actual deferral percentage and contribution percentage for said
         group of Highly Compensated Employees to satisfy the above
         restrictions.  The provisions of subsection (b) of this Section shall
         apply with respect to any Total Pre-Tax Contributions which cannot be
         credited to Pre-Tax Accounts because of the limitation contained in
         this subsection (d).

         Section 3.5  Application of Forfeitures.  As soon as practicable after
the valuation of all Accounts at the end of each Plan Year, all amounts
forfeited during that Plan Year shall first be applied to restore any forfeited
Employer Account required to be restored pursuant to Sections 6.5 and 6.8, and
any forfeitures in excess of the amount needed to restore any such Account may
be applied to pay administrative expenses in accordance with Section 7.4.  Any
remaining forfeitures for such Plan Year, if any, shall be allocated as a
qualified nonelective contribution if the Company determines in its discretion
that such a contribution shall be made to the Plan for such year in accordance
with Section 3.4(c).





                                      -13-
<PAGE>   17

         Section 3.6  Rollover Contributions.  With the consent of the
Committee, any Covered Employee (regardless of whether he or she is a
Participant) may contribute Rollover Property in the form of cash to the Plan.
Each contribution of Rollover Property shall be credited to a separate Rollover
Account to be established and maintained for the benefit of the contributing
Employee.  An Employee who is not a Participant, but for whom a Rollover
Account is being maintained, shall be accorded all of the rights and privileges
of a Participant under the Plan except that no contributions (other than
contributions of Rollover Property) shall be made for or on behalf of such
Employee until he or she meets the eligibility and participation requirements
of Article II.


                                  ARTICLE IV.

                           TRUST FUND AND VALUATIONS

         Section 4.1  Trust and Trustee.  All of the contributions paid to the
Trustee pursuant to this Plan and the Superseded Plan, together with the income
therefrom and the increments thereof, shall be held in trust by the Trustee
under the terms and provisions of the separate trust agreement between the
Trustee and the Company, a copy of which is attached hereto and incorporated
herein by this reference for all purposes, establishing a trust fund known as
the PIONEER NATURAL RESOURCES USA, INC. 401(k) TRUST for the exclusive benefit
of the Participants and their beneficiaries.

         Section 4.2  Trust Investment Options.  All amounts credited to a
Participant's Accounts may be invested in Company Stock and/or one or more of
the Investment Funds at the direction of such Participant in accordance with
the provisions of this Section.  The assets of the Trust (other than Company
Stock) shall be divided into such number and kind of separate and distinct
Investment Funds as the Committee in its absolute discretion shall authorize
from time to time.  The assets of the Trust allocated to a particular
Investment Fund shall be invested by the Trustee and/or one or more investment
managers duly appointed in accordance with the provisions of the trust
agreement establishing the Trust, as the case may be, in such type of property
acceptable to the Trustee as the Trustee is directed to acquire and hold for
such Investment Fund.  Upon becoming a Participant in the Plan, each
Participant shall direct, in the manner prescribed by the Committee in its
absolute discretion, that all amounts credited to his or her Accounts under the
Plan shall be invested, in percentage multiples authorized by the Committee, in
one or more of the Investment Funds.  Subject to such conditions and
limitations as the Committee in its absolute discretion may prescribe from time
to time for application to all Participants on a uniform basis, a Participant
may change his or her investment direction with respect to future contributions
or redirect the investment of the amounts credited to his or her Accounts
provided that notice of such change is delivered to or in the manner directed
by the Committee within such reasonable period of time prior to the effective
date thereof as the Committee may require.

         Section 4.3  Valuation and Adjustment of Accounts.  As of each
Valuation Date, the Trustee shall determine the fair market value of all assets
of the Trust with the value of the





                                      -14-
<PAGE>   18
assets of each Investment Fund being separately determined.  On the basis of
such valuations and in accordance with such procedures as may be specified from
time to time by the Committee, the portion of each Account invested in a
particular Investment Fund shall be adjusted by the Committee to reflect its
proportionate share of the income collected and accrued, realized and
unrealized profits and losses, expenses and all other transactions attributable
to that particular Investment Fund for the valuation period then ended.  All
cash dividends, stock dividends, stock splits and other amounts received by the
Trustee with respect to Company Stock held for an Account (including the
forfeiture account established pursuant to Section 3.5) shall be credited to
such Account.  The amount of any distribution, withdrawal or forfeiture shall
be determined on the basis of the most recent valuation preceding the date of
distribution, withdrawal or forfeiture, as the case may be.


                                   ARTICLE V.

                                    VESTING

         Section 5.1  Fully Vested Accounts.  The amounts credited to a
Participant's Pre-Tax Account, Prior Plan Pre-Tax Account, Rollover Account,
Prior Plan Employer Account and Mesa Employer Account shall be fully vested at
all times.

         Section 5.2  Vesting of Employer Account.

                 (a)      The amounts credited to the Employer Account of a
         Participant shall become fully vested upon the occurrence of any of
         the following events while the Participant is in the employ of (or on
         authorized leave of absence from) an Employer or Affiliated Company:
         (i) the completion of an Hour of Service by the Participant on or
         after the date he or she attains age 60, (ii) the Participant's death,
         or (iii) the Participant's Permanent Disability.  Unless sooner vested
         pursuant to the preceding sentence, and except as provided in
         subsection (b) of this Section, the amounts credited to a
         Participant's Employer Account shall vest in accordance with the
         following schedule:

<TABLE>
<CAPTION>
                    Period of Service                            
                 Completed by Participant                 Percentage Vested
                 ------------------------                 -----------------
                    <S>                                      <C>
                    Less than 1 year                           None
                    1 year                                      25%
                    2 years                                     50%
                    3 years                                     75%
                    4 or more years                            100%
</TABLE>

                 (b)      If a Participant makes an in-service withdrawal under
         Section 6.6 from his or her Employer Account at a time when the
         Participant is not fully vested, the Participant's vested amount in
         such account on any date thereafter shall be an amount





                                      -15-
<PAGE>   19
         X determined by the following formula: X = P(AB + D) - D.  For
         purposes of this formula, P is the Participant's vested percentage
         under the Plan's vesting schedule on the relevant date, AB is the
         account balance on the relevant date and D is the amount of the
         Participant's in-service withdrawal.


                                  ARTICLE VI.

                   VALUATIONS, DISTRIBUTIONS AND WITHDRAWALS

         Section 6.1  Time and Form of Distribution.  Distribution to a
Participant or beneficiary under this Article shall be made or commence being
made no later than 60 days after the close of the Plan Year in which the latest
of the following occurs:  (i) the Participant's Normal Retirement Date, (ii)
the tenth anniversary of the year in which the Participant commenced
participation in the Plan, or (iii) the Participant's separation from the
employment of an Employer for any reason other than his or her transfer to the
employment of another Employer or Affiliated Company.  In addition and any
provision of this Plan to the contrary notwithstanding, in the case of a
Participant who is a five-percent owner (as defined in Section 416(i) of the
Code) or at the election of any other Participant who attains age 70 1/2 prior
to January 1, 1999, distribution to such Participant under the Plan shall be
made or commence being made no later than April 1 of the calendar year
following the calendar year in which the Participant attains age 70 1/2.
Distributions that commence being made pursuant to the preceding sentence to a
Participant who has not separated from the employment of an Employer or
Affiliated Company shall be equal to the minimum amounts required to be
distributed pursuant to Section 401(a)(9) of the Code and the regulations
thereunder, without recalculation of life expectancy, with any amount remaining
upon the termination of the Participant's employment or death be paid in
accordance with Section 6.2 or Section 6.3, whichever is applicable, but with
any payments adjusted or accelerated as necessary to satisfy the requirements
of Section 401(a)(9) of the Code and the regulations thereunder.  Subject to
the provisions of this Article requiring that distributions and withdrawals be
made in the form of an annuity contract, distributions and withdrawals shall be
made in cash, except that amounts credited to an Account that are invested in
Company Stock may, at the election of the Participant, be distributed in the
form of Company Stock with cash in lieu of fractional shares.  Any provision of
this Plan to the contrary notwithstanding, (A) all distributions from the Plan
shall be made in accordance with Section 401(a)(9) of the Code and the
regulations thereunder, and (B) all optional forms of benefit under the Plan,
the Superseded Plan and the Mesa Profit-Sharing Plan that are protected
benefits under Section 411(d)(6) of the Code shall continue to be optional
forms of benefit for Participants to whom such optional forms of benefit apply
notwithstanding any subsequent amendment purporting to revise or delete any
such optional form of benefit.

         Section 6.2  Distribution of Retirement and Disability Benefits.

                 (a)      Upon the Retirement or Permanent Disability of a
         Participant, the Vested Interest of such Participant shall be
         distributed to such Participant by the





                                      -16-
<PAGE>   20
         Trustee at the direction of the Committee in a single distribution;
         provided, however, that if such Participant's Vested Interest exceeds
         $3,500 ($5,000 commencing January 1, 1998), he or she may elect to
         receive his or her Vested Interest in monthly, quarterly or annual
         installment distributions over a period of two or more years with the
         first such installment to be payable within 90 days after the end of
         the Plan Year in which the Participant's employment terminates.  Such
         installment payments may be made over a period of years not to exceed
         one or a combination of the following periods:  (i) the life of the
         Participant, (ii) the lives of the Participant and his or her
         designated beneficiary, (iii) a period certain not extending beyond
         the life expectancy of the Participant, and (iv) a period certain not
         extending beyond the joint life and last survivor expectancy of the
         Participant and his or her designated beneficiary.  Any provision of
         Section 6.3 to the contrary notwithstanding, if a Participant who
         elected installment payments dies prior to the distribution of the
         entire amount of his or her Vested Interest, the remaining portion
         thereof shall be distributed to his or her beneficiary or
         beneficiaries, as determined in accordance with Section 6.3(a), in a
         single distribution within 90 days after the end of the Plan Year
         during which the Participant died.  Notwithstanding the foregoing
         provisions of this Section 6.2, no distribution shall be made upon the
         Permanent Disability of a Participant prior to his or her Normal
         Retirement Date unless (i) such Participant elects to receive such
         distribution, or (ii) such Participant's Vested Interest does not
         exceed $3,500 ($5,000 commencing January 1, 1998).

                 (b)      Any provision of subsection (a) of this Section to
         the contrary notwithstanding, except as otherwise provided in this
         subsection (b), upon the Retirement or Permanent Disability of a
         Participant whose Vested Interest exceeds $3,500 ($5,000 commencing
         January 1, 1998), such Participant's Prior Plan Employer Account and
         Prior Plan Pre-Tax Account shall be distributed to him or her by the
         Trustee at the direction of the Committee in the form of a Qualified
         Joint and Survivor Annuity contract to be purchased from a company
         selected by the Committee and commencing in payment as soon as
         practicable.  At least 30 days but not more than 90 days prior to the
         date such annuity contract is to commence in payment, the Committee
         shall provide such Participant with a written explanation of (i) the
         terms and conditions of the Qualified Joint and Survivor Annuity, (ii)
         his or her right to make, and the effect of, an election to waive the
         Qualified Joint and Survivor Annuity form of benefit, (iii) the rights
         of his or her spouse with respect to the receipt and waiver of the
         Qualified Joint and Survivor Annuity, and (iv) the right to make, and
         the effect of, a revocation of an election to waive the Qualified
         Joint and Survivor Annuity.  After receiving such notice, the
         Participant may elect at any time during the 90-day period ending on
         the date the annuity contract is to commence in payment to waive the
         Qualified Joint and Survivor Annuity form of benefit and also may
         revoke any such election during such period.  Any such election to
         waive a Qualified Joint and Survivor Annuity form of benefit by a
         married Participant will be effective only if the spouse of such
         Participant consents in writing within the 90-day period preceding
         such date to both the election and the optional form of benefit
         selected by the Participant and such consent is witnessed by a member
         of the Committee or a





                                      -17-
<PAGE>   21
         notary public.  Any amount payable from the Prior Plan Employer
         Account or Prior Plan Pre-Tax Account upon the Retirement or Permanent
         Disability of a Participant who has elected to waive the Qualified
         Joint and Survivor Annuity form of benefit as provided above shall be
         distributed to such Participant by the Trustee at the direction of the
         Committee in accordance with subsection (a) of this Section.

         Section 6.3  Distribution of Death Benefit.

                 (a)      Except as otherwise provided in this Section, upon
         the death of a Participant, the Vested Interest of such Participant
         shall be distributed by the Trustee at the direction of the Committee
         to such Participant's beneficiary or beneficiaries determined in
         accordance with this subsection (a).  Any amount payable under the
         Plan upon the death of a married Participant shall be distributed to
         the surviving spouse of such Participant unless such Participant
         designates otherwise with the written consent of his or her spouse
         which is witnessed by a member of the Committee or a notary public.
         Any amount payable under the Plan upon the death of a Participant who
         is not married or who is married but has designated, as provided
         above, a beneficiary other than his or her spouse, shall be
         distributed to the beneficiary or beneficiaries designated by such
         Participant.  Such designation of beneficiary or beneficiaries shall
         be made in writing on a form prescribed by the Committee and, when
         filed with the Committee, shall become effective and remain in effect
         until changed by the Participant by the filing of a new beneficiary
         designation form with the Committee.  If an unmarried Participant
         fails to so designate a beneficiary, or in the event all of a
         Participant's designated beneficiaries are individuals who predecease
         such Participant, then the Committee shall direct the Trustee to
         distribute the amount payable under the Plan to such Participant's
         surviving spouse, if any, but if none, to such Participant's estate.
         All distributions under this subsection (a) shall be made in a single
         distribution as soon as practicable following a Participant's death;
         provided, however, a Participant may elect (or if the Participant does
         not elect, his or her designated beneficiary may elect) that
         distribution be made in monthly, quarterly or annual installments over
         a period of two or more years with the first such installment to be
         payable within 90 days after the end of the Plan Year in which the
         Participant died.  Installment payments may be made only to an
         individual over a period of years not to exceed one or a combination
         of the following periods:  (i) the life of the Participant's
         designated beneficiary, or (ii) a period certain not extending beyond
         the life expectancy of the Participant's designated beneficiary.

                 (b)  Any provision of subsection (a) of this Section to the
         contrary notwithstanding, except as otherwise provided in this
         subsection (b), upon the death of a married Participant whose Vested
         Interest exceeds $3,500 ($5,000 commencing January 1, 1998), such
         Participant's Prior Plan Employer Account and Prior Plan Pre-Tax
         Account shall be distributed to his or her surviving spouse in the
         form of a Qualified Preretirement Survivor Annuity contract to be
         purchased from a company selected by the Committee and commencing in
         payment on the date that would have been such Participant's Normal
         Retirement Date if he or she were still living.  The





                                      -18-
<PAGE>   22
         Committee shall provide each such married Participant with a written
         explanation of the Qualified Preretirement Survivor Annuity provided
         above, including the Participant's right to waive the distribution of
         such Qualified Preretirement Survivor Annuity with the consent of his
         or her spouse and to revoke any such waiver, within whichever of the
         following periods ends last: (i) the period beginning with the first
         day of the Plan Year in which the Participant attains the age of 32
         and ending with the close of the Plan Year preceding the Plan Year in
         which the Participant attains the age of 35, (ii) the one-year period
         after the individual becomes a Participant, or (iii) the one-year
         period after separation from employment in the case of a Participant
         who separates before attaining age 35.  Each married Participant may
         elect at any time prior to such Participant's death to waive the
         Qualified Preretirement Survivor Annuity form of benefit provided
         above so that his or her entire benefit may be paid to his or her
         designated beneficiary.  No election to waive the Qualified
         Preretirement Survivor Annuity will be effective upon the
         Participant's death unless such election designates a beneficiary that
         cannot be changed without spousal consent, the Participant's surviving
         spouse consents in writing to such election and such consent is
         witnessed by a member of the Committee or a notary public.  A married
         Participant may revoke any such election to waive the Qualified
         Preretirement Survivor Annuity at any time prior to his or her death.
         The amount payable under the Plan upon the death of a married
         Participant who has elected, as provided above, to waive the Qualified
         Preretirement Survivor Annuity shall be distributed in accordance with
         subsection (a) of this Section.  The surviving spouse of any deceased
         Participant may elect in writing after the Participant's death to
         receive the entire benefit otherwise payable to such surviving spouse
         in accordance with this subsection (a) of this Section.

         Section 6.4  Distribution of Separation from Employment Benefit.

                 (a)      If a Participant separates from the employment of an
         Employer or Affiliated Company for any reason other than his or her
         Retirement, Permanent Disability, death or transfer to the employment
         of another Employer or Affiliated Company, the Accounts of such
         Participant shall be retained in trust and shall continue to be
         credited with applicable earnings as provided in Section 4.3, and the
         Vested Interest of such Participant shall be distributed to him or her
         by the Trustee at the direction of the Committee in accordance with
         Section 6.2(a) as soon as practicable after his or her Normal
         Retirement Date (or, if the Participant dies prior to such date, the
         Vested Interest of such Participant shall be distributed upon his or
         her death in accordance with Section 6.3); provided, however, that (i)
         each such Participant shall have the right to elect on a form
         prescribed by the Committee to receive an early distribution of his or
         her Vested Interest as soon as practicable and (ii) the Committee
         shall require an early distribution of any such Participant's Vested
         Interest which does not exceed $3,500 ($5,000 commencing January 1,
         1998) in the form of a single distribution.  The Vested Interest of a
         Participant who elects to receive an early distribution shall be
         distributed to him or her in the same manner as provided in Section
         6.2(a) for a distribution upon Retirement or Permanent Disability.





                                      -19-
<PAGE>   23
         Any provision of this Plan to the contrary notwithstanding, for
         purposes of this Article a Participant shall not be treated as having
         separated from the employment of an Employer or Affiliated Company
         prior to such time that a distribution can be made to such Participant
         in accordance with Section 401(k) of the Code and the regulations
         thereunder.

                 (b)      Any provision of subsection (a) of this Section to
         the contrary notwithstanding, except as otherwise provided in this
         subsection (b), if a Participant's whose Vested Interest exceeds
         $3,500 ($5,000 commencing January 1, 1998) separates from the
         employment of an Employer or Affiliated Company for any reason other
         than his or her Retirement, Permanent Disability, death or transfer to
         the employment of another Employer or Affiliated Company, such
         Participant's Prior Plan Employer Account and Prior Plan Pre-Tax
         Account shall be distributed to such Participant by the Trustee at the
         direction of the Committee upon such Participant's Normal Retirement
         Date by payment of the entire amount in the form of a Qualified Joint
         and Survivor Annuity contract to be purchased from a company selected
         by the Committee and commencing in payment as soon as practicable
         thereafter (or, if the Participant dies prior to his or her Normal
         Retirement Date, the Vested Interest of such Participant under the
         Plan shall be distributed upon his or her death in accordance with
         Section 6.3); provided, however, that each such Participant shall have
         the right to elect on a form prescribed by the Committee to receive an
         early distribution of the amount credited to his or her Prior Plan
         Employer Account and Prior Plan Pre-Tax Account as soon as practicable
         after such election.  If a Participant elects under this subsection
         (b) to receive an early distribution of the amount credited to his or
         her Prior Plan Employer Account and Prior Plan Pre-Tax Account, such
         distribution shall be made in the form of (i) a Qualified Joint and
         Survivor Annuity contract to be purchased from a company selected by
         the Committee and commencing in payment as soon as practicable
         following such election, or (ii) upon satisfaction of the notice and
         waiver requirements of Section 6.2(b), in accordance with subsection
         (a) of this Section.

         Section 6.5  Forfeitures.

                 (a)  Unless sooner forfeited as provided below, any unvested
         portion of the Employer Account of a Participant who separates from
         the employment of an Employer or Affiliated Company for any reason
         other than his or her Retirement, Permanent Disability, death or
         transfer to the employment of another Employer or Affiliated Company
         shall be forfeited upon the earlier of the date of such Participant's
         death or the date such Participant incurs five consecutive One Year
         Breaks in Service unless such Participant is reemployed by an Employer
         or Affiliated Company prior to such date.

                 (b)  If a Participant receives a complete distribution of
         his or her Vested Interest under Section 6.4 by the close of the
         second Plan Year following the Plan Year in which his or her
         separation from employment occurs, any portion of such





                                      -20-
<PAGE>   24
         Participant's Employer Account which is not vested at the time of such
         distribution shall be forfeited at such time.  If a Participant who
         separates from the employment of an Employer or Affiliated Company for
         any reason other than his or her Retirement, Permanent Disability,
         death or transfer to the employment of another Employer or Affiliated
         Company, is not entitled to receive any distribution from the Plan due
         to the fact that such Participant has no Vested Interest, such
         Participant shall be deemed to have received a distribution from the
         Plan of his or her entire Vested Interest under the Plan and any
         amount credited to such Participant's Employer Account shall be
         forfeited at the time of such separation from employment.  If a
         Participant any portion of whose Employer Account is forfeited
         pursuant to this subsection (b) is reemployed as a Covered Employee
         prior to incurring five consecutive One Year Breaks in Service, the
         amount so forfeited shall be restored to such individual's Employer
         Account, whichever is applicable, out of current-year forfeitures or,
         if such forfeitures are insufficient, by an additional Employer
         contribution; provided, however, that no amount shall be restored to
         the Employer Account of an individual who previously received a
         distribution of the vested portion of his or her Employer Account
         unless he or she repays to the Plan, while a Covered Employee and
         within five years of the date of such reemployment, the full amount
         previously distributed from such Account for crediting to his or her
         Employer Account.

                 (c)      If a Participant who has not yet incurred five
         consecutive One Year Breaks in Service receives a distribution under
         Section 6.4 after the end of the second Plan Year following the year
         in which his or her separation from employment occurred, any portion
         of such Participant's Employer Account which is not vested at the time
         of such distribution shall be retained in such Account and shall be
         forfeited upon the earlier of the date of such Participant's death or
         the date such Participant incurs five consecutive One Year Breaks in
         Service unless such Participant is reemployed by an Employer or
         Affiliated Company prior to such date.  If a Participant receives a
         distribution from the Plan after the end of the second Plan Year
         following the year in which his or her separation from employment
         occurred and is reemployed by an Employer or Affiliated Company prior
         to incurring five consecutive One Years Breaks in Service, then the
         unvested balance in his or her Employer Account shall be transferred
         to a segregated account for such Participant and the amount that the
         Participant is entitled to receive from such segregated account as of
         any later date shall be an amount equal to X, which amount shall be
         determined in accordance with the following formula:  X = P(AB + D) -
         D, where P is the Participant's vested percentage at such later date,
         AB is the amount in his or her segregated account at such later date,
         and D is the amount distributed to the Participant in connection with
         his or her earlier separation from employment.

         Section 6.6  In-Service Withdrawals.

                 (a)      A Participant in the employ of an Employer may make --





                                      -21-
<PAGE>   25
                 (i)      a withdrawal of all or a portion (in multiples of 10%
                          or in whole dollar amounts) of the total amount
                          credited to his or her Rollover Account;

                (ii)      if the Participant has attained the age of 59 1/2, a
                          withdrawal of all or a portion (in multiples of 10%
                          or in whole dollar amounts) of the total vested
                          amount credited to his or her Accounts; or

               (iii)      a hardship withdrawal of such amount as the Committee
                          shall determine to be necessary to satisfy an
                          immediate and heavy financial need of such
                          Participant from his or her Pre-Tax Account and Prior
                          Plan Pre-Tax Account, other than earnings credited to
                          either such Account under this Plan or the Superseded
                          Plan for any period of time after December 31, 1988;

         provided, however, that (i) no withdrawal may be made unless written
         notice of such withdrawal is delivered to the Committee by the
         withdrawing Participant within such period of time prior to the
         effective date thereof as the Committee may prescribe in its
         discretion, (ii) no withdrawal may be made by a Participant to whom a
         loan from the Trust is then outstanding unless the Committee is
         satisfied that such loan will remain nontaxable and fully secured by
         the withdrawing Participant's Vested Interest following such
         withdrawal, and (iii) withdrawals from the Prior Plan Pre-Tax Account
         may be made only pursuant to the notice and consent requirements of
         Section 6.2(b).  The Committee shall direct the Trustee to distribute
         any withdrawn amount to such Participant as soon as practicable
         following the effective date of the withdrawal.  Any withdrawal from
         an Account pursuant to this Section shall be taken proportionally from
         each Investment Fund in which such Account is invested.  The Committee
         may prescribe uniform and nondiscriminatory rules and procedures
         limiting the number of times that a Participant may make withdrawals
         during a Plan Year and the minimum amount that a Participant may
         withdraw on any single occasion.

                 (b)      A hardship withdrawal will be considered to be made
         on account of an immediate and heavy financial need of a Participant
         only if the Committee determines that such withdrawal is on account of
         (i) expenses for medical care described in Section 213(d) of the Code
         previously incurred by such Participant or his or her spouse or
         dependents (as defined in Section 152 of the Code) or necessary for
         such individuals to obtain such care, (ii) costs directly related to
         the purchase of a principal residence for such Participant (excluding
         mortgage payments), (iii) payment of tuition and related educational
         fees for the next 12 months of post-secondary education for such
         Participant or his or her spouse, children or dependents (as so
         defined), or (iv) payments necessary to prevent the eviction of such
         Participant from his or her principal residence or foreclosure on the
         mortgage of such residence.

                 (c)      A hardship withdrawal will be considered to be
         necessary to satisfy an immediate and heavy financial need of a
         Participant only if the Committee determines that (i) the amount of
         such withdrawal is not in excess of the amount of such need





                                      -22-
<PAGE>   26
         plus any amounts necessary to pay any federal, state or local income
         taxes or penalties reasonably anticipated to result from the
         withdrawal, and (ii) such Participant has obtained all distributions
         and withdrawals, other than hardship withdrawals, and all nontaxable
         loans currently available under all plans maintained by the Employers.

                 (d)      Any provision of this Plan to the contrary
         notwithstanding, if a Participant makes a hardship withdrawal, (i) no
         Pre-Tax Contributions or Pre-Tax Bonus Contributions shall be made on
         behalf of such Participant for 12 months after receipt of such
         withdrawal, and (ii) the Total Pre-Tax Contributions made on behalf of
         such Participant for the calendar year immediately following the
         calendar year of such withdrawal shall not exceed the amount by which
         the adjusted $7,000 limit described in Section 3.1(e) for such next
         calendar year exceeds the amount of the Total Pre-Tax Contributions
         made on behalf of such Participant for the calendar year of such
         withdrawal.

         Section 6.7  Distributions to Minors and Persons Under Legal
Disability.  If any distribution under the Plan becomes payable to a minor or
other person under a legal disability, such distribution may be made to the
duly appointed guardian or other legal representative of the estate of such
minor or person under legal disability.

         Section 6.8  Benefits Payable to Missing Participant or Beneficiary.
If the Committee cannot locate a Participant or beneficiary entitled to a
distribution under this Plan within a period of three years after such
Participant or beneficiary becomes entitled to the distribution, the amounts
credited to the Accounts of such Participant or beneficiary shall be forfeited;
provided, however, that if a claim for any such forfeited amounts is
subsequently made by any person entitled to the distribution, such forfeited
amounts shall be restored (without adjustment for earnings or appreciation) out
of current-year forfeitures, or if such forfeitures are insufficient, by an
additional Employer contribution.

         Section 6.9  Plan Loans.

                 (a)      Subject to such conditions and limitations as the
         Committee may from time to time prescribe for application to all
         Participants and beneficiaries on a uniform basis, at the request of a
         Participant or beneficiary of a deceased Participant who is a party in
         interest (within the meaning of Section 3(14) of the Employee
         Retirement Income Security Act of 1974, as amended) with respect to
         the Plan (hereinafter called the "Borrower"), the Committee shall
         direct the Trustee to loan to such Borrower from his or her Pre-Tax
         Account and/or Prior Plan Pre-Tax Account an amount of money which,
         when added to the total outstanding balance of all other loans to such
         Borrower from the Plan or from a qualified employer plan (within the
         meaning of Section 72(p) of the Code) maintained by an Employer or
         Affiliated Company, does not exceed the lesser of (i) $50,000
         (reduced, however, by the excess, if any, of the highest total
         outstanding balance of all such other loans during the one-year period
         ending on the day before the date such loan is made, over the
         outstanding balance of





                                      -23-
<PAGE>   27
         all such other loans on the date such loan is made), or (ii) one-half
         of such Participant's vested interest under the Plan (or, in the case
         of a loan to a beneficiary, one-half of such beneficiary's Accounts).

                 (b)      Any such loan made to a Borrower shall be evidenced
         by a promissory note payable to the Trustee, shall bear a reasonable
         rate of interest, shall be secured by one-half of the Participant's
         vested interest under the Plan (or, in the case of a loan to a
         beneficiary, by one-half of such beneficiary's Accounts), shall be
         repayable in substantially equal payments no less frequently than
         quarterly and shall be repayable within five years or, in the case of
         a loan that is to be used to acquire any dwelling unit which within a
         reasonable period of time is to be used as the principal residence of
         the Participant, within such period greater than five years as shall
         be determined by the Committee in its absolute discretion.

                 (c)      Any provision of this Plan to the contrary
         notwithstanding, (i) the promissory note evidencing any such loan
         shall be held by the Trustee as a segregated investment allocated to
         and made solely for the benefit of the Account of the Borrower from
         which such loan was made, and (ii) no loan shall be made to a married
         Participant from a Prior Plan Pre-Tax Account unless the spouse of
         such Participant consents in writing thereto within the 90-day period
         preceding the date such loan is made and such consent is witnessed by
         a member of the Committee or a notary public.

         Section 6.10  Qualified Domestic Relations Orders.  Any provision of
this Plan to the contrary notwithstanding:

                 (a)      The Committee shall establish and maintain for each
         alternate payee named with respect to a Participant under a domestic
         relations order which is determined by the Committee to be a qualified
         domestic relations order (as defined in Section 414(p) of the Code)
         such separate Accounts as the Committee may deem to be necessary or
         appropriate to reflect such alternate payee's interest in the Accounts
         of such Participant.  Such alternate payee's Accounts shall be
         credited with the alternate payee's interest in the Participant's
         Accounts as determined under such qualified domestic relations order.
         The alternate payee may change investment direction with respect to
         his or her Account balances in accordance with Section 4.2 in the same
         manner as the Participant.

                 (b)      Except to the extent otherwise provided in the
         qualified domestic relations order naming an alternate payee with
         respect to a Participant, (i) the alternate payee may designate a
         beneficiary on a form prescribed by and filed with the Committee, (ii)
         if no such beneficiary is validly designated or if the designated
         beneficiary is a person who predeceases the alternate payee, the
         beneficiary of the alternate payee shall be the alternate payee's
         estate, and (iii) the beneficiary of the alternate payee shall be
         accorded under the Plan all of the rights and privileges of the
         beneficiary of a Participant.





                                      -24-
<PAGE>   28
                 (c)      An alternate payee named with respect to a
         Participant shall be entitled to receive a distribution from the Plan
         in accordance with the qualified domestic relations order naming such
         alternate payee.  Such distribution may be made only in a form
         provided under the Plan and shall include only such amounts as are
         vested.  If a qualified domestic relations order so provides, a lump
         sum distribution of the total vested amount credited to the alternate
         payee's Accounts may be made to the alternate payee at any time prior
         to the date the Participant named in such qualified domestic relations
         order attains his or her earliest retirement age (as defined in
         Section 414(p)(4)(B) of the Code).  To the extent provided by a
         qualified domestic relations order, the alternate payee named with
         respect to a Participant may make withdrawals (other than hardship
         withdrawals) from his or her Accounts in accordance with Article VI in
         the same manner as the Participant with respect to whom such alternate
         payee was named under said qualified domestic relations order.

                 (d)      If a portion of any unvested amount credited to the
         Employer Account of a Participant named in the qualified domestic
         relations order is credited to the Employer Account of the alternate
         payee named in such qualified domestic relations order, the portion
         credited to such Account of the alternate payee shall vest and/or be
         forfeited at the same time and in the same manner as such Account of
         the Participant.

         Section 6.11  Transfer of Eligible Rollover Distribution.  If a
Participant is entitled to receive an eligible rollover distribution (as
defined in Section 402(c) of the Code and the regulations thereunder) from the
Plan, such Participant may elect to have the Committee direct the Trustee to
transfer the entire amount of such distribution directly to any of the
following specified by such Participant:  an individual retirement account
described in Section 408(a) of the Code, an individual retirement annuity
described in Section 408(b) of the Code (other than an endowment contract), a
defined contribution plan qualified under Section 401(a) of the Code the terms
of which permit rollover contributions or an annuity plan described in Section
403(a) of the Code.  If the surviving spouse of a deceased Participant is
entitled to receive an eligible rollover distribution from the Plan, such
surviving spouse may elect to have the Committee direct the Trustee to transfer
the entire amount of such distribution directly to either an individual
retirement account described in Section 408(a) of the Code or an individual
retirement annuity described in Section 408(b) of the Code (other than an
endowment contract) specified by such surviving spouse.  If an alternate payee
under a qualified domestic relations order (as defined in Section 414(p) of the
Code) is the spouse or former spouse of the Participant specified in the
qualified domestic relations order, this Section shall apply to such alternate
payee as if the alternate payee were a Participant.  A distributee of an
eligible rollover distribution who is entitled to make an election under this
Section may specify that some portion less than the entire amount of such
distribution be transferred in accordance with this Section.





                                      -25-
<PAGE>   29
                                  ARTICLE VII.

                              PLAN ADMINISTRATION

         Section 7.1  401(k) Plan Committee.  The plan administrator of the
Plan shall be a 401(k) Plan Committee composed of at least three individuals
appointed by the Board of Directors of the Company.  Each member of the
Committee so appointed shall serve in such office until his or her death,
resignation or removal by the Board of Directors of the Company.  The Board of
Directors of the Company may remove any member of the Committee at any time by
giving written notice thereof to the members of the Committee.  Vacancies shall
likewise be filled from time to time by the Board of Directors of the Company.
The members of the Committee shall receive no remuneration from the Plan for
their services as Committee members.

         Section 7.2  Powers, Duties and Liabilities of the Committee.  The
Committee shall have discretionary and final authority to interpret and
implement the provisions of the Plan, including without limitation authority to
determine eligibility for benefits under the Plan, and shall perform all of the
duties and exercise all of the powers and discretion granted to it under the
terms of the Plan.  The Committee shall act by a majority of its members at the
time in office and such action may be taken either by a vote at a meeting or in
writing without a meeting.  The Committee may by such majority action authorize
any one or more of its members to execute any document or documents on behalf
of the Committee, in which event the Committee shall notify the Trustee in
writing of such action and the name or names of its member or members so
authorized to act.  Every interpretation, choice, determination or other
exercise by the Committee of any discretion given either expressly or by
implication to it shall be conclusive and binding upon all parties directly or
indirectly affected, without restriction, however, on the right of the
Committee to reconsider and redetermine such actions.  In performing any duty
or exercising any power herein conferred, the Committee shall in no event
perform such duty or exercise such power in any manner which discriminates in
favor of Highly Compensated Employees.  The Employers shall indemnify and hold
harmless each member of the Committee against any claim, cost, expense
(including attorneys' fees), judgment or liability (including any sum paid in
settlement of a claim with the approval of the Employers) arising out of any
act or omission to act as a member of the Committee appointed under this Plan,
except in the case of willful misconduct.

         Section 7.3  Rules, Records and Reports.  The Committee may adopt such
rules and procedures for the administration of the Plan as are consistent with
the terms hereof, and shall keep adequate records of the Committee's
proceedings and acts and of the status of the Participants' Accounts.  The
Committee may employ such agents, accountants and legal counsel (who may be
agents, accountants or legal counsel for an Employer) as may be appropriate for
the administration of the Plan.  The Committee shall at least annually provide
each Participant with a report reflecting the status of his or her Accounts in
the Trust and shall cause such other information, documents or reports to be
prepared, provided and/or





                                      -26-
<PAGE>   30
filed as may be necessary to comply with the provisions of the Employee
Retirement Income Security Act of 1974 or any other law.

         Section 7.4  Administration Expenses and Taxes.  Unless otherwise paid
by the Employers in their discretion, the Committee shall direct the Trustee to
pay all reasonable and necessary expenses (including the fees of agents,
accountants and legal counsel) incurred by the Committee in connection with the
administration of the Plan.  Should any tax of any character (including
transfer taxes) be levied upon the Trust assets or the income therefrom, such
tax shall be paid from and charged against the assets of the Trust.


                                 ARTICLE VIII.

                           AMENDMENT AND TERMINATION

         Section 8.1  Amendment.  The Board of Directors of the Company shall
have the right and power at any time and from time to time to amend this Plan,
in whole or in part, on behalf of all Employers.  Any such amendment made by
the Board of Directors of the Company shall be made by or pursuant to a
resolution duly adopted by the Board of Directors of the Company, and shall be
evidenced by such resolution or by a written instrument executed by such person
as the Board of Directors of the Company shall authorize for such purpose.
With the consent of the Board of Directors of the Company and subject to such
procedure as it may prescribe, the Board of Directors of each Employer shall
have the right and power at any time and from time to time to amend this Plan,
in whole or in part, with respect to the Plan's application to the Participants
of the particular amending Employer and the assets held in the Trust for their
benefit, or to transfer such assets or any portion thereof to a new trust for
the benefit of such Participants.  However, in no event shall any amendment or
new trust permit any portion of the trust fund to be used for or diverted to
any purpose other than the exclusive benefit of the Participants and their
beneficiaries, nor shall any amendment or new trust reduce a Participant's
Vested Interest under the Plan.

         Section 8.2  Termination.  The Board of Directors of the Company shall
have the right and power at any time to terminate this Plan on behalf of all
Employers, or to terminate this Plan as it applies to the Participants who are
or were employees of any particular Employer, by giving written notice of such
termination to the Committee and Trustee.  Any provision of this Plan to the
contrary notwithstanding, upon the termination or partial termination of the
Plan as to any Employer, or in the event any Employer should completely
discontinue making contributions to the Plan without formally terminating it,
all amounts credited to the Accounts of the affected Participants of that
particular Employer shall be fully vested.





                                      -27-
<PAGE>   31
                                  ARTICLE IX.

                              TOP-HEAVY PROVISIONS

         Section 9.1  Top-Heavy Definitions.  Unless the context clearly
indicates otherwise, when used in this Article:

                 (a)      "Top-Heavy Plan" means this Plan if, as of the
         Determination Date, the aggregate of the Accounts of Key Employees
         under the Plan exceeds 60% of the aggregate of the Accounts of all
         Participants and former Participants under the Plan.  The aggregate of
         the Accounts of any Participant or former Participant shall include
         any distributions (other than related rollovers or transfers from the
         Plan within the meaning of regulations under Section 416(g) of the
         Code) made from such individual's Accounts during the Plan Year or any
         of the four preceding Plan Years, but shall not include any unrelated
         rollovers or transfers (within the meaning of regulations under
         Section 416(g) of the Code) made to such individual's Accounts after
         December 31, 1983.  The Accounts of any Participant or former
         Participant who (i) is not a Key Employee for the Plan Year in
         question but who was a Key Employee in a prior Plan Year, or (ii) has
         not completed an Hour of Service during the five-year period ending on
         the Determination Date, shall not be taken into account.  The
         determination of whether the Plan is a Top-Heavy Plan shall be made
         after aggregating all other plans of an Employer and any Affiliated
         Company qualifying under Section 401(a) of the Code in which a Key
         Employee is a participant or which enables such a plan to meet the
         requirements of Section 401(a)(4) or 410 of the Code, and after
         aggregating any other plan of an Employer or Affiliated Company, which
         is not already aggregated, if such aggregation group would continue to
         meet the requirements of Sections 401(a)(4) and 410 of the Code and if
         such permissive aggregation thereby eliminates the top-heavy status of
         any plan within such permissive aggregation group.  The determination
         of whether this Plan is a Top-Heavy Plan shall be made in accordance
         with Section 416(g) of the Code.

                 (b)      "Determination Date" means, for purposes of
         determining whether the Plan is a Top-Heavy Plan for a particular Plan
         Year, the last day of the preceding Plan Year.

                 (c)      "Key Employee" means any Employee or former Employee
         (including a beneficiary of such Employee or former Employee) who at
         any time during the Plan Year or any of the four preceding Plan Years
         is:

                          (1)     an officer of the Employer who has
                 Compensation for any such Plan Year greater than 50% of the
                 amount in effect under Section 415(b)(1)(A) of the Code for
                 such Plan Year;

                          (2)     one of the 10 Employees owning (or considered
                 as owning within the meaning of Section 318 of the Code) the
                 largest interests in excess





                                      -28-
<PAGE>   32
                 of 0.5% in an Employer or Affiliated Company and having
                 Compensation for such Plan Year of more than the limitation in
                 effect under Section 415(c)(1)(A) of the Code;

                          (3)     a person owning (or considered as owning
                 within the meaning of Section 318 of the Code) more than 5% of
                 the outstanding stock of an Employer or stock possessing more
                 than 5% of the total combined voting power of all stock of an
                 Employer; or

                          (4)     a person who has Compensation for such Plan
                 Year from an Employer of more than $150,000 and who would be
                 described in paragraph (3) hereof if 1% were substituted for
                 5% in each place it appears in such paragraph.

         For the purposes of applying Section 318 of the Code to this
         subsection (c), subparagraph (C) of Section 318(a)(2) of the Code
         shall be applied by substituting 5% for 50%.  The rules of subsections
         (b), (c) and (m) of Section 414 of the Code shall not apply for
         purposes of determining ownership in an Employer under this subsection
         (c).

                 (d)      "Non-Key Employee" means any Employee or former
         Employee (including a beneficiary of such Employee or former Employee)
         who is not a Key Employee.

         Section 9.2  Minimum Contribution Requirement.  Any provision of this
Plan to the contrary notwithstanding, if the Plan is a Top-Heavy Plan for any
Plan Year commencing after December 31, 1996, then the Employers will
contribute to the Employer Account of each Non-Key Employee who is both
eligible to participate and in the employ of an Employer on the last day of
such Plan Year, an amount which, when added to the total amount of
contributions (excluding Total Pre-Tax Contributions) and forfeitures otherwise
allocable under the Plan for such Non-Key Employee for such year, shall equal
the lesser of (i) 3% of such Non-Key Employee's Limitation Compensation
(Compensation for any Plan Year commencing after December 31, 1997) for such
year or (ii) the amount of contributions (including Total Pre-Tax Contributions)
and forfeitures (expressed as a percentage of Limitation Compensation
(Compensation for any Plan Year commencing after December 31, 1997)) allocable
under the Plan for or on behalf of the Key Employee for whom such percentage is
the highest for the Plan Year after taking into account contributions under
other defined contribution plans maintained by the Employer in which a Key
Employee is a participant (as well as any other plan of an Employer which
enables such a plan to meet the requirements of Section 401(a)(4) or 410 of the
Code); provided, however, that no minimum contribution shall be made for a
Non-Key Employee under this Section for any Plan Year if the Employer maintains
another qualified plan under which a minimum benefit or contribution is being
accrued or made for such Plan Year for the Non-Key Employee in accordance with
Section 416(c) of the Code.  A Non-Key Employee who is not a Participant, but
for whom a contribution is made pursuant to this Section, shall be accorded all
of the





                                      -29-
<PAGE>   33
rights and privileges of a Participant under the Plan except that no
contributions (other than contributions pursuant to this Section) shall be made
for or on behalf of such Non-Key Employee until he or she meets the eligibility
and participation requirements of Article II.

         Section 9.3  Minimum Vesting Schedule.  Any provision of this Plan to
the contrary notwithstanding, if the Plan is a Top-Heavy Plan for any Plan
Year, then effective as of the first day of such Plan Year with respect to
Participants who complete an Hour of Service on or after such day, the vesting
schedule provided in Section 5.2 shall be applied to that portion of such
Participants' Employer Account which is attributable to any amounts credited to
his or her Employer Nonelective Contribution Account under the Superseded Plan
as in effect on September 30, 1997, as if to read as follows:

<TABLE>
<CAPTION>
             Period of Service                         
         Completed by Participant                       Percentage Vested
         ------------------------                       -----------------
            <S>                                               <C>
            Less than 3 years                                 None
            3 or more years                                   100%
</TABLE>


                                   ARTICLE X.

                        MISCELLANEOUS GENERAL PROVISIONS

         Section 10.1  Spendthrift Provision.  No right or interest of any
Participant or beneficiary under the Plan may be assigned, transferred or
alienated, in whole or in part, either directly or by operation of law, and no
such right or interest shall be liable for or subject to any debt, obligation
or liability of such Participant or beneficiary; provided, however, that
nothing herein shall prevent the payment of amounts from a Participant's
Accounts under the Plan in accordance with the terms of a court order which the
Committee has determined to be a qualified domestic relations order (as defined
in Section 414(p) of the Code).

         Section 10.2  Claims Procedure.  If any person (hereinafter called the
"Claimant") feels that he or she is being denied a benefit to which he or she
is entitled under the Plan, such Claimant may file a written claim for said
benefit with any member of the Committee.  Within 60 days of the receipt of
such claim the Committee shall determine and notify the Claimant as to whether
he or she is entitled to such benefit.  Such notification shall be in writing
and, if denying the claim for benefit, shall set forth the specific reason or
reasons for the denial, make specific reference to the pertinent provisions of
the Plan, and advise the Claimant that he or she may, within 60 days of the
receipt of such notice, in writing request to appear before the Committee for a
hearing to review such denial.  Any such hearing shall be scheduled at the
mutual convenience of the Committee or its designated representative and the
Claimant, and at such hearing the Claimant and/or his or her duly authorized
representative may examine any relevant documents and present evidence and
arguments to support the granting of the benefit being claimed.  The final
decision of the Committee with





                                      -30-
<PAGE>   34
respect to the claim being reviewed shall be made within 60 days following the
hearing thereon and the Committee shall in writing notify the Claimant of its
final decision, again specifying the reasons therefor and the pertinent
provisions of the Plan upon which such decision is based.  The final decision
of the Committee shall be conclusive and binding upon all parties having or
claiming to have an interest in the matter being reviewed.

         Section 10.3  Maximum Contribution Limitation.  Any provision of this
Plan to the contrary notwithstanding, the sum of (i) the Employer
contributions, (ii) the forfeitures, and (iii) the Participant contributions
(excluding rollover contributions and employee contributions to a simplified
employee pension allowable as a deduction, each within the meaning specified in
Section 415(c)(2) of the Code), allocated to a Participant with respect to a
Plan Year shall in no event exceed the lesser of $30,000 (as adjusted pursuant
to Section 415(d) of the Code to take into account any cost-of-living
increase) or 25% of such Participant's Limitation Compensation (Compensation
for any Plan Year commencing after December 31, 1997) for that year.  For the
purposes of applying the limitation imposed by this Section, each Employer and
its Affiliated Companies shall be considered a single employer, and all defined
contribution plans (meaning plans providing for individual accounts and for
benefits based solely upon the amounts contributed to such accounts and any
forfeitures, income, expenses, gains and losses allocated to such accounts)
described in Section 415(k) of the Code, whether or not terminated, maintained
by an Employer or its Affiliated Companies shall be considered a single plan.
If the total amount allocable to a Participant's Accounts for a particular Plan
Year would, but for this sentence, exceed the foregoing limitation, such
Participant's Total Pre-Tax Contributions shall be distributed to such
Participant first from any Pre-Tax Bonus Contributions and then, to the extent
necessary, from Pre-Tax Contributions.  Any Total Pre-Tax Contributions
distributed to a Participant pursuant to this Section shall not be taken into
account in determining such Participant's actual deferral percentage for
purposes of Section 3.4.

         Section 10.4  Employment Noncontractual.  The establishment of this
Plan shall not enlarge or otherwise affect the terms of any Employee's
employment with an Employer and an Employer may terminate the employment of any
Employee as freely and with the same effect as if this Plan had not been
adopted.

         Section 10.5  Limitations on Responsibility.  The Employers do not
guarantee or indemnify the Trust against any loss or depreciation of its assets
which may occur, nor guarantee the payment of any amount which may become
payable to a Participant or his or her beneficiaries pursuant to the provisions
of this Plan.  All payments to Participants and their beneficiaries shall be
made by the Trustee at the direction of the Committee solely from the assets of
the Trust and the Employers shall have no legal obligation, responsibility or
liability for any such payments.

         Section 10.6  Merger or Consolidation.  In no event shall this Plan be
merged or consolidated into or with any other plan, nor shall any of its assets
or liabilities be transferred to any other plan, unless each Participant would
be entitled to receive a benefit if the plan in which he or she then
participates terminated immediately following such merger,





                                      -31-
<PAGE>   35
consolidation or transfer, which is equal to or greater than the benefit he or
she would have been entitled to receive if the Plan had been terminated
immediately prior to such merger, consolidation or transfer.

         Section 10.7  Applicable Law.  This Plan shall be governed and
construed in accordance with the internal laws (and not the principles relating
to conflicts of laws) of the State of Texas except where superseded by federal
law.

         IN WITNESS WHEREOF, this Plan has been restated by Pioneer Natural
Resources USA, Inc. this 30th day of September, 1997, to be effective as of
October 1, 1997.

                                        PIONEER NATURAL RESOURCES USA, INC.



                                        By   /s/ Larry N. Paulsen 
                                          ---------------------------------
                                          Title:  Vice President





                                      -32-
<PAGE>   36

        V A N G U A R D   F I D U C I A R Y   T R U S T   C O M P A N Y

                         T R U S T   A G R E E M E N T



         THIS AGREEMENT OF TRUST (the "Agreement") effective the 1st day of
October, 1997, by and between PIONEER NATURAL RESOURCES USA, INC., a Delaware
corporation (the "Company "), and VANGUARD FIDUCIARY TRUST  COMPANY, a trust
company incorporated under Chapter 10 of the Pennsylvania Banking Code (the
"Trustee"),

                                   WITNESSETH


        WHEREAS, the Company has adopted and maintains a qualified profit
sharing plan and trust for the exclusive benefit of its employees known as the
PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN (the "Plan"); and

        WHEREAS, the 401(k) Plan Committee (the "Plan Administrator") is the
fiduciary named in the Plan as having the authority to control and manage the
operation and administration of the Plan; and

        WHEREAS, the Company and the Trustee desire to amend and restate the
Plan's related trust to update its language and make certain other changes;


        NOW, THEREFORE, in consideration of the mutual covenants contained
herein, the parties hereto, intending to be legally bound, hereby amend and
restate the Plan's related trust as the Pioneer Natural Resources USA, Inc.
401(k) Trust to read as follows:



                                    Pg. 1
<PAGE>   37
                                   ARTICLE I

                            CONTINUANCE OF THE TRUST

        Section 1.1. The Company and the Trustee hereby agree to the
continuance of a trust consisting of such sums as shall from time to time be
paid to the Trustee under the Plan and such earnings, income and appreciation
as may accrue thereon, which, less payments made by the Trustee to carry out
the purposes of the Plan, are referred to herein as the "Fund".  The Trustee
shall carry out the duties and responsibilities herein specified, but shall be
under no duty to determine whether the amount of any contribution by the
Company or any Participant is in accordance with the terms of the Plan nor
shall the Trustee be responsible for the collection of any contributions
required under the Plan.

        Section 1.2.  The Fund shall be held, invested, reinvested and
administered by the Trustee in accordance with the terms of the Plan and this
Agreement solely in the interest of Participants and their Beneficiaries and
for the exclusive purpose of providing benefits to Participants and their
Beneficiaries and defraying reasonable expenses of administering the Plan.
Except as provided in Section 4.2, no assets of the Plan shall inure to the
benefit of the Company.

        Section 1.3.  The Trustee shall pay benefits and expenses from the Fund
only upon the written direction of the Plan Administrator.  The Trustee shall
be fully entitled to rely on such directions furnished by the Plan
Administrator, and shall be under no duty to ascertain whether the directions
are in accordance with the provisions of the Plan.


                                   ARTICLE II

                             INVESTMENT OF THE FUND

        Section 2.1.  The Plan Administrator shall have the exclusive authority
and discretion to select the investment funds ("Investment Funds") available
for investment under the Plan. The Plan Administrator shall notify the Trustee
in writing of the selection of the Investment Funds currently available for
investment under the Plan, and any changes thereto.





                                     Pg. 2
<PAGE>   38
        Section 2.2.  Each Participant shall have the exclusive right, in
accordance with the provisions of the Plan, to direct the investment by the
Trustee of all amounts allocated to the separate accounts of the Participant
under the Plan among any one or more of the available Investment Funds.  All
investment directions by Participants shall be timely furnished to the Trustee
by the Plan Administrator, except to the extent such directions are transmitted
telephonically or otherwise by Participants directly to the Trustee or its
delegate in accordance with rules and procedures established and approved by
the Plan Administrator and communicated to the Trustee.  In making any
investment of the assets of the Fund, the Trustee shall be fully entitled to
rely on such directions furnished to it by the Plan Administrator or by
Participants in accordance with the Plan Administrator's approved rules and
procedures, and shall be under no duty to make any inquiry or investigation
with respect thereto.  If the Trustee receives any contribution under the Plan
that is not accompanied by instructions directing its investment, the Trustee
shall immediately notify the Plan Administrator of that fact, and the Trustee
may, in its discretion, hold or return all or a portion of the contribution
uninvested without liability for loss of income or appreciation pending receipt
of proper investment directions.  Otherwise, it is specifically intended under
the Plan and this Agreement that the Trustee shall have no discretionary
authority to determine the investment of the assets of the Fund.

        Section 2.3.  Subject to the provisions of Sections 2.1 and 2.2, the
Trustee shall have the authority, in addition to any authority given by law, to
exercise the following powers in the administration of the Trust:

        (a)  to invest and reinvest all or a part of the Fund in accordance 
        with Participants' investment directions in any available Investment 
        Fund selected by the Plan Administrator without restriction to
        investments authorized for fiduciaries, including, without limitation on
        the amount that may be invested therein, any common, collective or
        commingled trust fund maintained by the Trustee.  Any investment in, and
        any terms and conditions of, any common, collective or commingled  trust
        fund available only to employee trusts which meets the requirements of
        the Internal Revenue Code of 1986, as amended (the "Code"), or
        corresponding provisions of subsequent income tax laws of the United
        States, shall constitute an integral part of this Agreement and the
        Plan;

        (b)       to invest all or any portion of the assets of the Fund in the
        Sarofim Trust Co. Employee Benefit Investment Trust or any other group
        trust which is exempt from tax under Section 501(a) of the Internal
        Revenue Code by reason of qualifying under Section 401(a) of the
        Internal





                                     Pg. 3
<PAGE>   39
        Revenue Code.  The instruments establishing any such group trust, as
        amended from time to time, are hereby incorporated by this reference
        and made a part of this Agreement for all purposes, and shall govern
        the investment of any asset of this Trust which is invested in any such
        group trust.

        (c)       to dispose of all or any part of the investments, securities,
        or other property which may from time to time or at any time constitute
        the Fund in accordance with the investment directions by Participants
        furnished to it pursuant to Section 2.2 or the written directions by
        the Plan Administrator furnished to it pursuant to Section 1.3, and to
        make, execute and deliver to the purchasers thereof good and sufficient
        deeds of conveyance therefor, and all assignments, transfers and other
        legal instruments, either necessary or convenient for passing the title
        and ownership thereto, free and discharged of all trusts and without
        liability on the part of such purchasers to see to the application of
        the purchase money;

        (d)       to hold cash uninvested to the extent necessary to pay
        benefits or expenses of the Plan;

        (e)       to cause any investment of the Fund to  be registered in the
        name of the Trustee or the name of its nominee or nominees or to retain
        such investment unregistered or in a form permitting transfer by
        delivery; provided that the books and records of the Trustee shall at
        all times show that all such investments are part of the Fund;

        (f)       to vote in person or by proxy with respect to all mutual fund
        shares that are credited to a Participant's separate account under the
        Plan solely in accordance with written directions furnished to it by
        the Participant; provided that the Trustee shall be responsible for
        delivering to each Participant all notices, proxies and proxy
        soliciting materials relating to any shares of one or more of the
        regulated investment companies offered by the Vanguard Group, Inc. that
        are credited to the Participant's separate account under the Plan;

        (g)       upon the written direction of the Plan Administrator, to
        apply for, purchase, hold or transfer any life insurance, retirement
        income, endowment or annuity contract;





                                     Pg. 4
<PAGE>   40
        (h)       to consult and employ any suitable agent to act on behalf of
        the Trustee and to contract for legal, accounting, clerical and other
        services deemed necessary by the Trustee to manage and administer the
        Fund according to the terms of the Plan and this Agreement;

        (i)       upon the written direction of the Plan Administrator, to make
        loans from the Fund to Participants in amounts and on terms approved by
        the Plan Administrator in accordance with the provisions of the Plan;
        provided that the Plan Administrator shall have the responsibility for
        collecting all loan repayments required to be made under the Plan and
        for furnishing the Trustee with copies of all promissory notes
        evidencing such loans;  and

        (j)       to pay from the Fund all taxes imposed or levied with respect
        to the Fund or any part thereof under existing or future laws, and to
        contest the validity or amount of any tax, assessment, claim or demand
        respecting the Fund or any part thereof.

        Section 2.4.  Except as may be authorized by regulations promulgated by
the Secretary of Labor, the Trustee shall not maintain the indicia of ownership
in any assets of the Fund outside of the jurisdiction of the district courts of
the United States.

        Section 2.5  In addition to the rights of Participants to direct the
Trustee as to the voting of mutual fund shares, each Participant (or
Beneficiary of a deceased Participant) shall have the right to direct  the
Trustee as to the manner of voting and the exercise of all other rights which a
shareholder of record has with respect to shares (and fractional shares) of
Company Stock which have been allocated to the Participant's separate account
(including, but not limited to the right to sell or retain shares in a public
or private tender offer).  Upon receipt of instructions from Participants, the
Trustee shall vote or exercise the right with respect to such stock in
accordance  with Participant instructions.  All shares (and fractional shares)
of Company Stock for which the Trustee has not received timely voting or
exercise directions shall be voted or exercised by the Trustee in the same
proportion that the shares (and fractional shares) of Company Stock for which
the Trustee received timely voting or exercise directions from other Plan
Participants are to be voted or exercised, except in the case where the Trustee
determines that to do so would be inconsistent with the provisions of Title I
of the Employee Retirement Income Security Act of 1974, as amended ("ERISA").
Notwithstanding anything herein to the contrary, in the event of a tender offer
for Company Stock, the Trustee shall not tender any shares (or fractional
shares) of Company Stock for which it does not receive





                                     Pg. 5
<PAGE>   41
timely directions to tender such shares (or fractional shares) from
Participants, except in the case where the Trustee determines that to do so
would be inconsistent with the provisions of Title I of ERISA.  The Trustee
shall be responsible for delivering to each Participant all notices, proxies
and proxy soliciting materials relating to any shares of  Company Stock that
are credited to the Participants' separate accounts under the Plan


                                  ARTICLE III

                          DUTIES AND RESPONSIBILITIES

        Section 3.1.  The Trustee, the Company and the Plan Administrator shall
each discharge their assigned duties and responsibilities under this Agreement
and the Plan solely in the interest of Participants and their Beneficiaries in
the following manner:

          (a)     for the exclusive purpose of providing benefits to
          Participants and their Beneficiaries and defraying reasonable
          expenses of administering the Plan;

          (b)     with the care, skill, prudence, and diligence under the
          circumstances then prevailing that a prudent person acting in a like
          capacity and familiar with such matters would use in the conduct of
          an enterprise of a like character and with like aims;

          (c)     by diversifying the available investments under the Plan so
          as to minimize the risk of large losses, unless under the
          circumstances it is clearly prudent not to do so; and

          (d)     in accordance with the provisions of the Plan and this Trust
          Agreement insofar as they are consistent with the provisions of
          ERISA.

        Section 3.2.  The Trustee shall keep full and accurate accounts of all
receipts, investments, disbursements and other transactions hereunder,
including such specific records as may be agreed upon in writing between the
Company and the Trustee.  All such accounts, books and records shall be open to
inspection and audit at all reasonable times by any authorized representative
of the Company or the Plan Administrator.  A Participant may examine only those
individual account records pertaining directly to him.





                                     Pg. 6
<PAGE>   42
        Section 3.3.  Within 120 days after the end of each Plan Year or within
120 days after its removal or resignation, the Trustee shall file with the Plan
Administrator a written account of the administration of the Fund showing all
transactions effected by the Trustee subsequent to the period covered by the
last preceding account to the end of such Plan Year or date of removal or
resignation and all property held at its fair market value at the end of the
accounting period.  Upon approval of such accounting by the Plan Administrator,
neither the Company nor the Plan Administrator shall be entitled to any further
accounting by the Trustee.  The Plan Administrator may approve such accounting
by written notice of approval delivered to the Trustee or by failure to express
objection to such accounting in writing delivered to the Trustee within 90 days
from the date on which the accounting is delivered to the Plan Administrator.

        Section 3.4.  In accordance with the terms of the Plan, the Trustee
shall open and maintain separate accounts in the name of each Participant in
order to record all contributions by or on behalf of the Participant under the
Plan and any earnings, losses and expenses attributable thereto.  The Plan
Administrator shall furnish the Trustee with written instructions enabling the
Trustee to allocate properly all contributions and other amounts under the Plan
to the separate accounts of Participants.  In making such allocation, the
Trustee shall be fully entitled to rely on the instructions furnished by the
Plan Administrator and shall be under no duty to make any inquiry or
investigation with respect thereto.

        Section 3.5.  The Trustee shall furnish each Participant with
statements at least annually, or more frequently as may be agreed upon with the
Company, reflecting the current fair market value of the Participant's separate
accounts under the Plan.

        Section 3.6.  The Trustee shall not be required to determine the facts
concerning the eligibility of any Participant to participate in the Plan, the
amount of benefits payable to any Participant or Beneficiary under the Plan, or
the date or method of payment or disbursement.  The Trustee shall be fully
entitled to rely solely upon the written advice and directions of the Plan
Administrator as to any such question of fact.

        Section 3.7.  Unless resulting from the Trustee's negligence, willful
misconduct, lack of good faith, or breach of its fiduciary duties under this
Agreement or ERISA, the Company shall indemnify and save harmless the Trustee
from, against, for and in respect of any and all damages, losses, obligations,
liabilities,





                                     Pg. 7
<PAGE>   43
liens, deficiencies, costs and expenses, including without limitation,
reasonable attorney's fees incident to any suit, action, investigation, claim
or proceedings suffered, sustained, incurred or required to be paid by the
Trustee in connection with the Plan or this Agreement.  The Company may
discharge its obligation to pay attorney's fees under this Section 3.7 by
offering to provide appropriate and competent legal counsel to represent the
Trustee, and such legal counsel shall be approved by the Trustee (which
approval shall not be unreasonably withheld).  In such event, the Trustee may
elect to retain counsel of its own choosing at its own expense.


                                   ARTICLE IV

                            PROHIBITION OF DIVERSION

        Section 4.1.  Except as provided in Section 4.2 of this Article, at no
time prior to the satisfaction of all liabilities with respect to Participants
and their Beneficiaries under the Plan shall any part of the corpus or income
of the Fund be used for, or diverted to, purposes other than for the exclusive
benefit of Participants or their Beneficiaries, or for defraying reasonable
expenses of administering the Plan.

        Section 4.2.  The provisions of Section 4.1 notwithstanding,
contributions made by the Company under the Plan may be returned to the Company
under the following conditions:

          (a)     If a contribution is made by mistake of fact, such
          contribution may be returned to the Company within one year of the
          payment of such contribution;

          (b)     Contributions to the Plan are specifically conditioned upon
          their deductibility under the Code.  To the extent a deduction is
          disallowed for any such contribution, it may be returned to the
          Company within one year after the disallowance of the deduction.
          Contributions which are not deductible in the taxable year in which
          made but are deductible in subsequent taxable years shall not be
          considered to be disallowed for purposes of this subsection; and

          (c)     Contributions to the Plan are specifically conditioned on
          initial qualification of the Plan under the Code.  If the Plan is
          determined to be disqualified, contributions made in respect of any
          period subsequent to the effective date of such disqualification may
          be returned to the Company within one year after the date of denial
          of qualification.





                                     Pg. 8
<PAGE>   44
                                   ARTICLE V

                       APPOINTMENT OF INVESTMENT MANAGERS

       Section 5.1.  The Plan Administrator may appoint one or more Investment
Managers with respect to some or all of the assets of the Fund as contemplated
by section 402(c)(3) of ERISA.  Any such investment manager shall acknowledge
to the Plan Administrator in writing that it accepts such appointment and that
it is an ERISA fiduciary with respect to the Plan and the Fund.  The Plan
Administrator shall provide the Trustee with a copy of the written agreement
(and any amendments thereto) between the Plan Administrator and the Investment
Manager.  By notifying the Trustee of the appointment of an Investment Manager,
the Plan Administrator shall be deemed to certify that such Investment Manager
meets the requirements of section 3(38) of ERISA.  The authority of the
Investment Manager shall continue until the Plan Administrator rescinds the
appointment or the Investment Manager has resigned.

       Section 5.2.  The assets with respect to which a particular Investment
Manager has been appointed shall be specified by the Plan Administrator and
shall be segregated in a separate account for the Investment Manager (the
"Separate Account") and the Investment Manager shall have the power to direct
the Trustee in every aspect of the investment of the assets of the Separate
Account.  Any provision of this Trust to the contrary notwithstanding, the
Investment Manager shall be responsible for making any proxy voting or tender
offer decisions with respect to securities held in the Separate Account and the
Investment Manager shall maintain a record of the reasons for the manner in
which it voted proxies or responded to tender offers.  The Trustee shall not be
liable for the acts or omissions of an Investment Manager and shall have no
liability or responsibility for acting or not acting pursuant to the direction
of, or failing to act in the absence of, any direction from an Investment
manager, unless the Trustee knows that by such action or failure to act it
would be itself committing a breach of fiduciary duty or participating in a
breach of fiduciary duty by such Investment Manager, it being the intention of
the parties that the Trustee shall have the full protection of section 405(d)
of ERISA.





                                     Pg. 9
<PAGE>   45
                                   ARTICLE VI

               COMMUNICATION WITH PLAN ADMINISTRATOR AND COMPANY

        Section 6.1.  Whenever the Trustee is permitted or required to act upon
the directions or instructions of the Plan Administrator, the Trustee shall be
entitled to act upon any written communication signed by any person or agent
designated to act as or on behalf of the Plan Administrator.  Such person or
agent shall be so designated either under the provisions of the Plan or in
writing by the Company and their authority shall continue until revoked in
writing.  The Trustee shall incur no liability for failure to act on such
person's or agent's instructions or orders without written communication, and
the Trustee shall be fully protected in all actions taken in good faith in
reliance upon any instructions, directions, certifications and communications
believed to be genuine and to have been signed or communicated by the proper
person.

        Section 6.2. The Company shall notify the Trustee in writing as to the
appointment, removal or resignation of any person designated to act as or on
behalf of the Plan Administrator.  After such notification, the Trustee shall
be fully protected in acting upon the directions of, or dealing with, any
person designated to act as or on behalf of the Plan Administrator until it
receives notice to the contrary. The Trustee shall have no duty to inquire into
the qualifications of any person designated to act as or on behalf of the Plan
Administrator.


                                  ARTICLE VII

                             TRUSTEE'S COMPENSATION

        Section 7.1.  The Trustee shall be entitled to reasonable compensation
for its services as is agreed upon with the Company.  If approved by the Plan
Administrator, the Trustee shall also be entitled to reimbursement for all
direct expenses properly and actually incurred on behalf of the Plan.  Such
compensation or reimbursement shall be paid to the Trustee out of the Fund
unless paid directly by the Company.


                                  ARTICLE VIII

                       RESIGNATION AND REMOVAL OF TRUSTEE

        Section 8.1.  The Trustee may resign at any time by written notice to
the Company which shall be effective 30 days after delivery unless prior
thereto a successor Trustee shall have been appointed.





                                     Pg. 10
<PAGE>   46
        Section 8.2.  The Trustee may be removed by the Company at any time
upon 30 days written notice to the Trustee; such notice, however, may be waived
by the Trustee.

        Section 8.3.  The appointment of a successor Trustee hereunder shall be
accomplished by and shall take effect upon the delivery to the resigning or
removed Trustee, as the case may be, of written notice of the Company
appointing such successor Trustee, and an acceptance in writing of the office
of successor Trustee hereunder executed by the successor so appointed.  Any
successor Trustee may be either a corporation authorized and empowered to
exercise trust powers or one or more individuals.  All of the provisions set
forth herein with respect to the Trustee shall relate to each successor Trustee
so appointed with the same force and effect as if such successor Trustee had
been originally named herein as the Trustee hereunder.  If within 30 days after
notice of resignation shall have been given under the provisions of this
article a successor Trustee shall not have been appointed, the resigning
Trustee or the Company may apply to any court of competent jurisdiction for the
appointment of a successor Trustee.

        Section 8.4.  Upon the appointment of a successor Trustee, the
resigning or removed Trustee shall transfer and deliver the Fund to such
successor Trustee, after deducting the actual amount of its reasonable expenses
incurred in the settlement of its account, and the amount of any compensation
due to it.  If the sums so deducted are not sufficient for such purposes, the
resigning or removed Trustee shall be entitled to reimbursement for any
deficiency from the Company.


                                   ARTICLE IX

                              INSURANCE  COMPANIES

        Section 9.1.  If any contract issued by an insurance company shall form
a part of the Trust assets, the insurance company shall not be deemed a party
to this Agreement.  A certification in writing by the Trustee as to the
occurrence of any event contemplated by this Agreement or the Plan shall be
conclusive evidence thereof and the insurance company shall be protected in
relying upon such certification and shall incur no liability for  so doing.
With respect to any action under any such contract, the insurance company may
deal with the Trustee as the sole owner thereof and need not see that any
action of the Trustee is authorized by this Agreement or the Plan.  Any change
made or action taken by an insurance company upon the direction





                                     Pg. 11
<PAGE>   47
of the Trustee shall fully discharge the insurance company from all liability
with respect thereto, and it need not see to the distribution or further
application of any moneys paid by it to the Trustee or paid in accordance with
the direction of the Trustee.


                                   ARTICLE X

                AMENDMENT AND TERMINATION OF THE TRUST AND PLAN

        Section 10.1.  The Company may, by delivery to the Trustee of an
instrument in writing, amend, terminate or partially terminate this Agreement
at any time; provided, however, that no amendment shall increase the duties or
liabilities of the Trustee without the Trustee's consent;  and, provided
further, that no amendment shall divert any part of the Fund to any purpose
other than providing benefits to Participants and their Beneficiaries or
defraying reasonable expenses of administering the Plan.

        Section 10.2.  If the Plan is terminated in whole or in part, or if the
Company permanently discontinues its contributions to the Plan, the Trustee
shall distribute the Fund or any part thereof in such manner and at such times
as the Plan Administrator shall direct in writing.


                                   ARTICLE XI

                            MISCELLANEOUS PROVISIONS

        Section 11.1.  Unless the context of this Agreement clearly indicates
otherwise, the terms defined in the Plan shall, when used herein, have the same
meaning as in the Plan.

        Section 11.2.  Except as otherwise required in the case of any
qualified domestic relations order within the meaning of Section 414(p) of the
Code, the benefits or proceeds of any allocated or unallocated portion of the
assets of the Fund and any interest of any Participant or Beneficiary arising
out of or created by the Plan either before or after the Participant's
retirement shall not be subject to execution, attachment, garnishment or other
legal or judicial process whatsoever by any person, whether creditor or
otherwise, claiming against such Participant or Beneficiary.  No Participant or
Beneficiary shall have the right to alienate, encumber or assign any of the
payments or proceeds or any other interest arising out of or created





                                     Pg. 12
<PAGE>   48
by the Plan and any action purporting to do so shall be void.  The provisions
of this Section shall apply to all Participants and Beneficiaries, regardless
of their citizenship or place of residence.

        Section 11.3.  Nothing contained in this Agreement or in the Plan shall
require the Company to retain any Employee in its service.

        Section 11.4. Any person dealing with the Trustee may rely upon a copy
of this Agreement and any amendments thereto certified to be true and correct
by the Trustee.

        Section 11.5.  The Trustee hereby acknowledges receipt of a copy of the
Plan. The Company will cause a copy of any amendment to the Plan to be
delivered to the Trustee.

        Section 11.6.  The construction, validity and administration of this
Agreement and the Plan shall be governed by the laws of the Commonwealth of
Pennsylvania, except to the extent that such laws have been specifically
superseded by ERISA.

        IN WITNESS WHEREOF, the parties hereto have executed this Agreement to
be effective as of the day and year first above written.

Attest:                                 PIONEER NATURAL RESOURCES USA, INC
                              
                              
                                        By  /s/ LARRY PAULSEN
- ---------------------------------         -------------------------------------
                              
                              
Attest:                                 VANGUARD FIDUCIARY TRUST COMPANY
                              
                              
                                        By  /s/ R. GREGORY BARTON
- ---------------------------------         -------------------------------------
                                            Managing Director




                                     Pg. 13
<PAGE>   49
                                        PIONEER NATURAL RESOURCES USA, INC.

                                        By
                                           -------------------------------------

THE STATE OF TEXAS                      Section
                                        Section
COUNTY OF_______________________________Section

          BEFORE ME, the undersigned authority, a Notary Public in and for said
County and State, on this day personally appeared
___________________________________________________________, known to
me to be the person and officer whose name is subscribed to the foregoing
instrument and acknowledged to me that the same was the act of the said Pioneer
Natural Resources USA, Inc., a Delaware corporation, and that he executed the
same as the act of such corporation for the purposes and consideration therein
expressed, and in the capacity therein stated.

          GIVEN UNDER MY HAND AND SEAL OF OFFICE, this the _________ day of
___________________________________, 1997.


                                        ----------------------------------------
                                        Notary Public, State of Texas

My commission expires

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

                                        VANGUARD  FIDUCIARY  TRUST  COMPANY

                                        By
                                          --------------------------------------
                                          Managing Director

THE STATE OF PENNSYLVANIA               Section
                                        Section
COUNTY OF CHESTER                       Section

          BEFORE ME, the undersigned authority, a Notary Public in and for said
County and State, on this day personally appeared
____________________________________________________________________, known to
me to be the person and officer whose name is subscribed to the foregoing
instrument and acknowledged to me that the same was the act of said Vanguard
Fiduciary Trust Company, a trust company incorporated under Chapter 10 of the
Pennsylvania Banking Code, and that he executed the same as the act of such
corporation for the purposes and consideration therein expressed, and in the
capacity therein stated.

          GIVEN UNDER MY HAND AND SEAL OF OFFICE, this the _________ day of
___________________________________, 1997.


                                        ----------------------------------------
                                        Notary Public, State of Pennsylvania

My commission expires


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



                                     Pg. 14

<PAGE>   1
                                                                     EXHIBIT 5.1




                       [VINSON & ELKINS L.L.P LETTERHEAD]



                                October 31, 1997


Pioneer Natural Resources Company
1400 Williams Square West
5205 North O'Connor Boulevard
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, as amended (the "ACT"), of
400,000 shares of common stock, par value $0.01 per share, of the Company which
may be purchased in the open market and offered from time to time under the
Pioneer Natural Resources USA, Inc. Profit Sharing 401(k) Plan (the "PLAN") and
of an indeterminate amount of interests in the Plan (the "INTERESTS") under the
Company's Registration Statement on Form S-8 (the "REGISTRATION STATEMENT")
filed with the Securities and Exchange Commission (the "COMMISSION") on October
31, 1997.

         In reaching the opinions set forth herein, we have examined and are
familiar with originals or copies, certified or otherwise identified to our
satisfaction, of such documents and records of the Company and such statutes,
regulations and other instruments as we deemed necessary or advisable for
purposes of this opinion, including (i) the Registration Statement, (ii) the
Restated Certificate of Incorporation of the Company, as filed with the
Secretary of State of the State of Delaware, (iii) the Bylaws of the Company,
(iv) certain minutes of meetings of, and resolutions adopted by, the Board of
Directors of the Company authorizing the issuance and offering of the Interests
in the Plan, and (v) the Plan.

         We have assumed that (i) all information contained in all documents we
reviewed is true, correct and complete, (ii) all signatures on all documents we
reviewed 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 the documents we examined were competent to execute and deliver such
documents.


         Based on the foregoing, and having due regard for the legal
considerations we deem relevant, we are of the opinion that the Interests, when
offered and issued by the Company pursuant to the terms of the Plan, will be
legally issued, fully paid and non-assessable.

         This opinion is limited in all respects to the laws of the State of
Texas, the Delaware General Corporation Law 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.
<PAGE>   2
         This opinion letter may be filed as an exhibit to the Registration
Statement.  In giving this consent, we do not thereby admit that we come 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 23.1


                        CONSENT OF INDEPENDENT AUDITORS


The Board of Directors
Pioneer Natural Resources Company


We consent to the use of our reports incorporated herein by reference.  Our
report 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.


                                      /s/ KPMG Peat Marwick LLP

                                          KPMG PEAT MARWICK LLP

Midland, Texas
October 29, 1997

<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
October 29, 1997

<PAGE>   1
                                                                    EXHIBIT 23.3


                       CONSENT OF INDEPENDENT ACCOUNTANTS


We consent to the incorporation by reference in this Form S-8 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.


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

                                             COOPERS & LYBRAND L.L.P.

Houston, Texas
October 30, 1997


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