As filed with the Securities and Exchange Commission on June 26, 2002


                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM 11-K

             / x / ANNUAL REPORT PURSUANT TO SECTION 15(D) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                   For the fiscal year ended December 31, 2001

                                       OR

           /   / TRANSITION REPORT PURSUANT TO SECTION 15 (D) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

              For the transition period from _________ to _________

                          Commission File No. 333-39249

A.    Full title of the plan and the address of the plan, if different from that
of the issuer named below:

                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN


B.    Name of issuer of the securities held pursuant to the plan and the address
of its principal executive officer:


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







                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN


                 Financial Statements and Supplemental Schedule

    As of December 31, 2001 and 2000 and for the year ended December 31, 2001

                       With Report of Independent Auditor










                                       2






                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                      AS OF DECEMBER 31, 2001 AND 2000 AND
                      FOR THE YEAR ENDED DECEMBER 31, 2001


                                Table of Contents


                                                                      Page


Report of Independent Auditor....................................       4

Statements of Net Assets Available for Benefits as of
    December 31, 2001 and 2000...................................       5

Statement of Changes in Net Assets Available for Benefits
   for the year ended December 31, 2001..........................       6

Notes to Financial Statements....................................       7

Schedule H; Line 4i - Schedule of Assets (Held At End of
   Year) as of December 31, 2001.................................      12

Signatures.......................................................      13

Index to Exhibits................................................      14






                                       3






                          Report of Independent Auditor


To the Participants and the Plan Administrator
of Pioneer Natural Resources USA, Inc. 401(k) Plan:


We have audited the accompanying statements of net assets available for benefits
of Pioneer  Natural  Resources USA, Inc. 401(k) Plan (the "Plan") as of December
31, 2001 and 2000, and the related  statement of changes in net assets available
for benefits for the year ended December 31, 2001.  These  financial  statements
are the  responsibility  of the  Plan's  management.  Our  responsibility  is to
express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with auditing standards generally accepted
in the United States. Those standards require that we plan and perform the audit
to obtain reasonable  assurance about whether the financial  statements are free
of material misstatement. An audit includes examining, on a test basis, evidence
supporting  the amounts and  disclosures in the financial  statements.  An audit
also includes assessing the accounting principles used and significant estimates
made by  management,  as well as  evaluating  the  overall  financial  statement
presentation.  We believe  that our audits  provide a  reasonable  basis for our
opinion.

In our opinion,  the financial  statements  referred to above present fairly, in
all  material  respects,  the net assets  available  for benefits of the Plan at
December  31,  2001 and 2000,  and the changes in its net assets  available  for
benefits for the year ended  December 31, 2001,  in conformity  with  accounting
principles generally accepted in the United States.

Our audits were performed for the purpose of forming an opinion on the financial
statements taken as a whole. The  accompanying  supplemental  schedule of assets
(held at end of year) as of December 31, 2001,  is presented  for the purpose of
additional  analysis and is not a required part of the financial  statements but
is  supplementary  information  required by the  Department of Labor's Rules and
Regulations for Reporting and Disclosure  under the Employee  Retirement  Income
Security Act of 1974. This  supplemental  schedule is the  responsibility of the
Plan's management.  The supplemental schedule has been subjected to the auditing
procedures  applied  in our  audits  of the  financial  statements  and,  in our
opinion,  is fairly stated in all material respects in relation to the financial
statements taken as a whole.



                                       Ernst & Young LLP


Fort Worth, Texas
June 4, 2002






                                       4







                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN


                 Statements of Net Assets Available for Benefits




                                                          December 31,
                                                   --------------------------
                                                       2001           2000
                                                   -----------    -----------

                                                            
Investments at fair value:
  Vanguard Primecap Fund........................   $17,759,069    $21,148,244
  Vanguard Prime Money Market Fund..............    10,618,942     12,394,091
  Vanguard 500 Index Fund.......................     8,538,931      9,400,834
  Vanguard Windsor II Fund......................     7,489,819      6,525,824
  Vanguard - ST Corporate Fund..................     3,482,011      3,112,481
  Vanguard Total Bond Market Index Fund.........       875,098        220,638
  Vanguard International Growth Fund............       746,402      1,028,195
  Vanguard Asset Allocation Fund................       201,309        122,262
  Vanguard Explorer Fund........................         6,653            -
  Sarofim Equity Fund...........................    11,325,152     12,688,210
  Pioneer Natural Resources Stock Fund .........     4,199,189      5,326,283
                                                    ----------     ----------
                                                    65,242,575     71,967,062

Participants' loans.............................     1,359,059      1,220,876
                                                    ----------     ----------
                                                    66,601,634     73,187,938

Participant contributions receivable............       112,610            -
Unallocated administrative expenses.............        (9,525)           -
                                                    ----------     ----------
  Net assets available for benefits.............   $66,704,719    $73,187,938
                                                    ==========     ==========




                 See accompanying notes to financial statements.


                                       5









                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN


            Statement of Changes in Net Assets Available for Benefits
                      For the year ended December 31, 2001





                                                         
Additions to net assets attributed to:
  Investment income:
     Interest and dividend income........................   $ 1,413,151

  Employee contributions.................................     3,100,872
  Rollovers..............................................        70,908
                                                             ----------
     Total additions.....................................     4,584,931
                                                             ----------
Deductions from net assets attributed to:
  Net depreciation in fair value of investments..........     6,201,703
  Distributions to participants..........................     4,808,482
  Fees...................................................        57,965
                                                             ----------
     Total deductions....................................    11,068,150
                                                             ----------
Net decrease.............................................    (6,483,219)

Net assets available for benefits:
  Beginning of year......................................    73,187,938
                                                             ----------
  End of year............................................   $66,704,719
                                                             ==========





                 See accompanying notes to financial statements.


                                       6









                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          NOTES TO FINANCIAL STATEMENTS
                           December 31, 2001 and 2000

Note 1.     Description of Plan

       The following  description  of the  Pioneer  Natural Resources USA,  Inc.
401(k) Plan (the "Plan") provides only general information.  Participants should
refer to the Summary Plan Description for a complete  description of the Plan, a
copy of  which  is  available  to each  participant  from  the  Pioneer  Natural
Resources USA, Inc. 401(k) Plan Committee (the "Plan  Administrator").  The Plan
is subject to the provisions of the Employee  Retirement  Income Security Act of
1974 ("ERISA").

       General

       The Plan is a  defined contribution  plan established  under the Internal
Revenue Code (the "Code")  Section 401 on January 1, 1990 covering all employees
of  Pioneer  Natural  Resources  USA,  Inc.  (the  "Employer"),  a  wholly-owned
subsidiary of Pioneer Natural Resources Company. Regular full-time employees and
part-time  employees are eligible to participate in the Plan on the first day of
the month  following their date of hire. The Plan assets are held in a trust and
certain  administrative  functions such as  maintenance of account  balances and
allocation of earnings are performed by Vanguard  Fiduciary  Trust Company,  the
trustee of the trust (the "Trustee").

       Contributions

       Participants  may contribute  to the Plan an  amount of not less than two
percent nor more than 12 percent of their annual  salary.  An Employer  match is
contributed in cash to the Pioneer  Natural  Resources  USA, Inc.  Matching Plan
("Matching Plan") at an amount equal to 200 percent of the first five percent of
basic  compensation  contributed  by a participant  to the Plan. On December 31,
2001,  participant  contributions  amounting to $112,610  were in transit to the
Trustee and have been recorded as  participant  contributions  receivable in the
accompanying  Statement of Net Assets  Available  for Benefits as of December 1,
2001.  See  Note 7 for  information  regarding  the  merger  of the Plan and the
Matching Plan effective January 1, 2002.

       Participant Accounts

       Each  participant's   account  is   credited   with   the   participant's
contributions and an allocation of Plan earnings. Plan earnings are allocated to
each participant's  account by fund in proportion to their fund balance relative
to the total fund balance.

       Participants may borrow from  their accounts a  minimum of $1,000 up to a
maximum of $50,000, or 50 percent of their account's vested balances,  whichever
amount is less.  The loans  are  secured  by the  balance  in the  participant's
account.  Participant  loans bear  interest at an annual rate equal to the prime
borrowing rate at the inception of the loan plus one percent. Loan principal and
interest is paid ratably through payroll deductions.

       Investment Options

       During the  Plan year ended December 31, 2001,  participants were able to
allocate their contributions among the following  registered  investment company
funds and the Pioneer Natural Resources Stock Fund:

       Registered Investment Company Funds:

       o      Vanguard Primecap Fund  -  Seeks  long-term  growth of  capital by
              investing in  stocks of companies with above-average prospects for
              continued earnings growth,  strong industry  positions and skilled
              management teams.


                                       7






                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          NOTES TO FINANCIAL STATEMENTS
                           December 31, 2001 and 2000


Note 1.     Description of Plan (continued)

       o      Vanguard Prime Money Market Fund  -  Seeks to  provide high income
              and a stable  share price  of $1 by investing in short-term,  high
              quality money market instruments issued by financial institutions,
              non-financial  corporations,  the  United  States  government  and
              United States federal agencies.

       o      Vanguard 500 Index Fund  -  Seeks to  provide long-term  growth of
              capital and income from dividends by holding all of the 500 stocks
              that  make  up  the  Standard & Poor's  500  Composite Stock Price
              Index, a widely recognized benchmark of United States stock market
              performance.

       o      Vanguard Windsor II Fund  -  Seeks to provide  long-term growth of
              capital  and a  reasonable  level  of  income  from  dividends  by
              investing  in a diversified group  of undervalued  or out-of-favor
              stocks of  large capitalization  companies.  The stocks  generally
              sell at prices below the overall market average compared  to their
              dividend income and future return potential.

       o      Vanguard - ST Corporate Fund  -  Seeks to  provide a high level of
              income while  maintaining a  high degree of stability of principal
              by investing in short-term bonds, including high quality corporate
              and United States Treasury securities.

       o      Vanguard Total Bond Market Index Fund  -  Seeks to generate a high
              level  of  interest  income by  investing in  high-credit quality,
              corporate and United States Treasury securities.

       o      Vanguard International Growth Fund  -  Seeks to  provide long-term
              growth  of  capital  by  investing  in stocks of  companies  based
              outside the United States.  Stocks are selected from  more than 15
              countries.

       o      Vanguard Asset Allocation Fund - Seeks to maximize total return by
              investing in common stocks, bonds and money market instruments.

       o      Vanguard Explorer Fund  -  Seeks  long-term  growth of  capital by
              investing  in a  diversified  group of  small-company stocks  with
              prospects for above-average growth.

       o      Sarofim Equity Fund  -  Seeks to provide high growth of capital by
              investing in a  broadly diversified  portfolio of large companies.
              Income is a secondary goal.

       Pioneer Natural Resources Stock Fund  -  The  Pioneer  Natural  Resources
       Stock Fund is  designed to  provide  long-term growth of  capital through
       increases in the value of the common stock of the Company.  Dividends, if
       any, are reinvested to purchase more shares.

       Vesting

       As is  described in more  detail in "Contributions" above,  participants'
contributions   and  Plan  earnings  are   maintained  in  the  Plan.   Employer
contributions are maintained in the Matching Plan, together with the earnings of
the Matching Plan.


                                       8






                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          NOTES TO FINANCIAL STATEMENTS
                           December 31, 2001 and 2000


Note 1.     Description of Plan (continued)

       Participants are immediately vested in their voluntary contributions made
into the Plan,  plus the  actual  Plan  earnings  thereon.  Certain  participant
account  balances  that were  merged  into the Plan from  predecessor  plans and
account  balances  that will be  merged  into the Plan  from the  Matching  Plan
effective  January 1, 2002 (see Note 7,  below),  retain the  vesting  schedules
provided for in the predecessor plans' documents.  A participant is fully vested
in the Matching Plan after four years of continuous service.

       Payments of Benefits

       If the total value of the  vested portion of the participant's account is
$5,000 or less, payment will be made in one lump sum as soon as administratively
possible.  If the total value of the vested portion of the participant's account
exceeds  $5,000,  payment  will  occur  at age  70-1/2  unless  the  participant
terminates,  retires or becomes disabled prior to age 70-1/2  and consents to an
earlier  distribution date by filing a written request to the Plan Administrator
within  90  days  prior  to  the  date  the  participant  wishes  to  receive  a
distribution.  Except for participant accounts that have a total vested value of
$5,000 or less,  distributions to terminated,  retired or disabled  participants
will be annuities,  but may be  installments or lump sum payments if so directed
by the participant.  A participant's  beneficiary will receive the participant's
account balance in the event of a participant's death.

       Withdrawal of Benefits

       Employees  may withdraw  their  vested  assets in the  Plan under certain
hardship  conditions as defined in the Plan agreement.  Terminated  participants
may also withdraw their vested assets in the Plan.

       Plan Termination

       Although it has not  expressed any intent to do so,  the Employer has the
right under the Plan,  subject to the  provisions  of ERISA to  discontinue  its
contributions  at any time or to terminate  the Plan. In the event of the Plan's
termination  or the complete  discontinuance  of Employer  contributions  to the
Plan, participants will become fully vested in their accounts.

Note 2.     Summary of Significant Accounting Policies

       Basis of Presentation

       The  accompanying  financial  statements  have  been  prepared  under the
accrual basis of accounting in accordance with accounting  principles  generally
accepted in the United States  ("GAAP").  Benefit  payments made to participants
are recorded upon distribution.

       Investment Valuation

       Investments  are  valued  at  fair  value  as determined by  the Trustee.
Investment fair values are determined as follows:

       1.   Investments in  securities  traded on national  securities exchanges
            are valued at the last reported sales price on the last business day
            of the year.


                                       9






                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          NOTES TO FINANCIAL STATEMENTS
                           December 31, 2001 and 2000


Note 2.     Summary of Significant Accounting Policies (continued)

       2.   Investments  in  money  market  funds  are  valued  at  cost,  which
            approximates fair value.

       3.   Securities traded on  over-the-counter markets and listed securities
            for which no sales were reported on that date are valued at the mean
            between the last reported bid and asked prices.

       4.   Investments in  restricted securities and other security investments
            that do not  have an  established market are valued at fair value as
            determined by the Trustee.

       5.   Participant loans receivable  are valued  at their  unpaid principal
            balance, which approximates fair value.

       Security Transactions and Investment Income

       Security transactions  are accounted for on a trade-date basis.  Expenses
incurred with transactions,  if any, are added to the purchase price or deducted
from the  selling  price at the time of the  transactions.  Dividend  income  is
recorded on the ex-dividend  date.  Income from other investments is recorded as
earned on an accrual basis.

       Use of Estimates

       The preparation of financial statements  in conformity with GAAP requires
the Plan's  management to make estimates and assumptions that affect the amounts
reported in the financial  statements  and  accompanying  notes.  Actual results
could differ from those estimates.

Note 3.     Investments

       The Trustee  holds the  Plan's  investments  and  executes all investment
transactions.  All investment  information disclosed in the financial statements
and the accompanying  schedule,  including investments held at December 31, 2001
and 2000,  interest and dividend  income,  and net depreciation in fair value of
investments  for the year ended  December 31, 2001, was obtained or derived from
information  supplied to the Plan  Administrator  and  certified as complete and
accurate by the Trustee.

       During 2001,  the Plan's  investments  (including investments  purchased,
sold and held during the year) depreciated in fair value as follows:


                                                       
         Registered Investment Company Funds              $ 6,170,997
         Pioneer Natural Resources Stock Fund                  30,706
                                                           ----------
                                                          $ 6,201,703
                                                           ==========


Note 4.     Administrative Expenses

       Administrative expenses incurred by the Plan were $57,965 during the year
ended December 31, 2001. The Employer may pay certain  expenses  incurred in the
establishment and administration of the Plan, including expenses and fees of the
Trustee,  but is not  obligated  to do so.  Any  Plan  expenses  not paid by the
Employer  are paid from the Plan's  earnings  or from  account  forfeitures.  In
addition  to  administrative  expenses  paid by the  Plan,  Plan  administrative
expenses of $5,690 were paid by the  Employer  during 2001.  Account  forfeiture
balances in the Plan were  $28,566 and $74,024 as of December 31, 2001 and 2000,
respectively.


                                       10






                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          NOTES TO FINANCIAL STATEMENTS
                           December 31, 2001 and 2000


Note 5.     Tax Status of the Plan

       The Plan  received a  determination  letter  from  the  Internal  Revenue
Service ("IRS") dated January 14, 1999, stating that the Plan is qualified under
Section  401(a) of the Code and,  therefore,  the  related  trust is exempt from
taxation.  The  Plan is  required  to  operate  in  conformity  with the Code to
maintain its qualification. The Plan has been amended and restated subsequent to
the  receipt  of the  determination  letter.  The  Plan  has  applied  for a new
determination  letter on February 19, 2002,  but has not yet received a response
from the IRS on this application.  The Plan  Administrator  believes the Plan is
being operated in compliance  with the applicable  requirements of the Code and,
therefore,  believes  that the Plan is  qualified  and the related  trust is tax
exempt.

Note 6.     Related Party Transactions

       Certain Plan  investments are in shares or units of registered investment
company funds that are managed by the Trustee and the Pioneer Natural  Resources
Stock Fund. Plan  transactions in registered  investment  company funds that are
managed by the Trustee and the Pioneer  Natural  Resources Stock Fund qualify as
party-in-interest transactions.

Note 7.     Subsequent Event - Trust Amendment

       Effective January 1, 2002, the Pioneer Natural Resources USA, Inc. 401(k)
Trust was  amended to allow the merger of the  Matching  Plan into the Plan.  In
connection with the merger, $24,031,142 of Matching Plan assets were transferred
into the Plan on January 1, 2002.  No  additional  benefits will accrue into the
Matching  Plan on or after the  January 1, 2002  effective  date of the  merger.
Future matching  contributions will be made under the merged plan, which will be
renamed as the Pioneer Natural Resources USA, Inc. 401(k) and Matching Plan (the
"Merged  Plans").  Voluntary  participant  contributions  and matching  Employer
contributions  into the Merged Plans will each continue under the same terms and
vesting  attributes as  originally  provided for under the Plan and the Matching
Plan.


                                       11









                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN


         Schedule H; Line 4i - Schedule of Assets (Held At End of Year)
                                 EIN: 75-2516853
                                Plan Number: 001

                             As of December 31, 2001


                                                               (c)
                                                          Description of
                        (b)                            investment including
                Identity of issuer,                   maturity date, rate of                (e)
                borrower, lessor,                    interest, collateral, par            Current
 (a)            or similar party                        or maturity value                  Value
-----    ---------------------------------    ---------------------------------------    -----------

                                                                                
  *      Vanguard Fiduciary Trust Company     Vanguard Primecap Fund -
                                                344,702 shares                           $17,759,069
  *      Vanguard Fiduciary Trust Company     Vanguard Prime Money Market Fund -
                                                10,618,942 shares                         10,618,942
  *      Vanguard Fiduciary Trust Company     Vanguard 500 Index Fund -
                                                80,640 shares                              8,538,931
  *      Vanguard Fiduciary Trust Company     Vanguard Windsor II Fund -
                                                292,685 shares                             7,489,819
  *      Vanguard Fiduciary Trust Company     Vanguard - ST Corporate Fund -
                                                321,812 shares                             3,482,011
  *      Vanguard Fiduciary Trust Company     Vanguard Total Bond Market Index Fund -
                                                 86,302 shares                               875,098
  *      Vanguard Fiduciary Trust Company     Vanguard International Growth
                                                Fund - 49,727 shares                         746,402
  *      Vanguard Fiduciary Trust Company     Vanguard Asset Allocation Fund  -
                                                 9,230 shares                                201,309
  *      Vanguard Fiduciary Trust Company     Vanguard Explorer Fund - 110 shares              6,653
  *      Fayez Sarofim & Co.                  Sarofim Equity Fund - 231,930 shares        11,325,152
  *      Pioneer Natural Resources Company    Pioneer Natural Resources Stock Fund -
                                                605,944 units                              4,199,189
  *      Participants' loans                  Interest rates range from 7% to 10.5%        1,359,059
                                                                                          ----------
                                                                                         $66,601,634
                                                                                          ==========
--------------------------
*Party in-interest

Note:   Column (d) is  not  applicable  since  all investments  are  participant
        directed.





                                       12









                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                               S I G N A T U R E S


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


                          PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                          By:   Pioneer Natural Resources USA, Inc. 401(k) Plan
                                Committee


Date: June 26, 2002       By:    /s/ Larry N. Paulsen
                                ------------------------------------------
                                Larry N. Paulsen
                                Chairman


Date: June 26, 2002       By:    /s/ Richard P. Dealy
                                ------------------------------------------
                                Richard P. Dealy


Date: June 26, 2002       By:    /s/ Kevin Schepel
                                ------------------------------------------
                                Kevin Schepel


Date: June 26, 2002       By:    /s/ David W. Simpson
                                ------------------------------------------
                                David W. Simpson


Date: June 26, 2002       By:    /s/ Susan A. Spratlen
                                ------------------------------------------
                                Susan A. Spratlen



                                       13








                 PIONEER NATURAL RESOURCES USA, INC. 401(k) PLAN

                                INDEX TO EXHIBITS



Exhibit
Number             Description                                 Page
-------            -----------                                 ----

  23.1             Consent of Ernst & Young LLP                 15




                                       14