EXHIBIT 99.1


                          FOURTH SUPPLEMENTAL INDENTURE

     THIS  FOURTH  SUPPLEMENTAL  INDENTURE  dated  as of  July  15,  2004  (this
"Supplemental  Indenture"),  is entered  into among  Pioneer  Natural  Resources
Company, a Delaware corporation (the "Company"), and The Bank of New York, a New
York banking  association,  as trustee (the "Trustee").  Capitalized  terms used
herein and not  otherwise  defined have the meanings set forth in the  Indenture
referred to below.

                                    RECITALS

    A.   The Company and the  Trustee  are parties  to that  certain  Indenture,
         dated as of January 13, 1998  (the "Indenture"),  pursuant to which the
         Company may from  time to time issue  its debentures,  notes,  bonds or
         other evidences of indebtedness (collectively, the "Debt Securities").

    B.   The Company  has  issued  pursuant  to  the  Indenture  and the  Second
         Supplemental Indenture,  dated April 11, 2000 (the "Second Supplemental
         Indenture"), among the Company,  Pioneer Natural Resources USA, Inc., a
         Delaware corporation, as Guarantor  (the "Guarantor"), and the Trustee,
         $425,000,000  aggregate  principal  amount  of 9-5/8%  Senior Notes due
         April 1, 2010 (the "9-5/8% Notes").

    C.   The  Company  has  issued  pursuant  to the  Indenture  and  the  Third
         Supplemental Indenture, dated April 30,  2002  (the "Third Supplemental
         Indenture"),  among  the  Company,   the  Guarantor  and  the  Trustee,
         $150,000,000 aggregate  principal amount of 7.50% Senior Notes Due 2012
         (the "7.50% Notes").

    D.   On June 10, 2004, the Company offered to exchange the 9-5/8% Notes, the
         7.50% Notes  and the Company's  8 1/4%  Senior  Notes  due 2007 for new
         5.875% Senior Notes  due 2016  (the "New Notes"),  subject to the terms
         and conditions described  in the Exchange Circular dated June 10, 2004,
         as supplemented by  the Supplement  to Exchange Circular dated June 25,
         2004  (together,  the  "Exchange Circular"),  and the related Letter of
         Transmittal  and   Consent  dated  June  10,  2004,   (the  "Letter  of
         Transmittal"),  which  Exchange Circular  solicited the  consent of the
         holders of the 9-5/8%  Notes and  the 7.50%  Notes to  amend the Second
         Supplemental  Indenture  and  the  Third   Supplemental  Indenture   to
         permanently eliminate,  in the  event the  9-5/8% Notes and 7.50% Notes
         receive   certain   investment   grade   ratings,   certain   operating
         restrictions  (such offers  to exchange  as set  forth in  the Exchange
         Circular  and  the  Letter of  Transmittal,  including any  amendments,
         modifications or supplements thereto, the "Exchange Offers").

    E.   Promptly following the  execution  and  delivery  of this  Supplemental
         Indenture,  the Company plans  to accept tenders in the Exchange Offers
         and to  issue,  pursuant to  the Indenture  and the  Fifth Supplemental
         Indenture,   to  be  dated  July  15,  2004  (the  "Fifth  Supplemental
         Indenture"),  among the Company and the Trustee, $526,875,000 aggregate
         principal amount of the New Notes in connection with exchanges pursuant
         to the  Exchange  Offer,  such  that  there  will  have  been  redeemed
         $275,125,000  aggregate  principal  amount  of  the  9-5/8%  Notes  and
         $133,825,000 aggregate principal amount of the 7.50%  Notes pursuant to
         the Exchange Offers, such that there will then be outstanding under the
         Indenture  (after  giving  effect  to  the  Exchange  Offers  and prior
         redemptions) $64,044,000 aggregate principal amount of the 9-5/8% Notes
         and $16,175,000 aggregate principal amount of the 7.50% Notes.

    F.   Section  9.02  of  the  Indenture  provides  that,  with the consent of
         Holders representing  a majority in  aggregate principal  amount of the
         Notes then outstanding, the Company, when authorized by a resolution of
         the Board of  Directors,  and the  Trustee may  enter into an indenture
         supplemental  to  the   Indenture  for  the  purpose   of  amending  or
         supplementing the Indenture or modifying the rights of Holders (subject
         to certain exceptions).








     G.  The Company  desires and has  requested the  Trustee to join with it in
         entering into this  Supplemental Indenture for  the purpose of amending
         the Indenture  in  certain respects as permitted by Section 9.02 of the
         Indenture.

     H.  The  Company,  in  connection  with  the  Exchange Offer, has solicited
         consents to this  Supplemental Indenture  upon the terms and conditions
         set forth in the Exchange Offer.

     I.  The execution and  delivery of  this  Supplemental  Indenture  has been
         authorized by resolution of the Board of Directors of the Company.

     J.  The Company (i) has  received the  consent of  the Holders of, and will
         accept for exchange under the  Exchange Offer,  more than a majority in
         principal  amount of the  outstanding 9-5/8% Notes and the 7.50% Notes,
         all as certified by an  Officer's Certificate  delivered to the Trustee
         simultaneously  with the  execution and  delivery  of this Supplemental
         Indenture,  (ii) has  delivered to  the Trustee simultaneously with the
         execution and  delivery  of this  Supplemental Indenture  an Opinion of
         Counsel  relating  to this  Supplemental  Indenture as  contemplated by
         Section  9.03 of  the Indenture,  and  (iii)  has  satisfied all  other
         conditions required  under  Article 9  of the  Indenture to  enable the
         Company and the Trustee to enter into this Supplemental Indenture.

     NOW, THEREFORE, in consideration of the mutual agreements and covenants set
forth  herein,  the parties  hereto agree,  subject to the terms and  conditions
hereinafter set forth, as follows for the benefit of the Trustee and the Holders
of the Notes:

         Section 1.     Amendments to Second Supplemental Indenture.
                        -------------------------------------------

                  (a)   Section 4.18.  Section 4.18 of  the  Second Supplemental
Indenture is hereby amended to read in its entirety as follows:

                  "Section 4.18. Suspension or Elimination of Covenants.  During
                  any period of time that (a) the Notes have an Investment Grade
                  Rating from either  of the  Rating Agencies and (b) no Default
                  or Event of  Default has occurred  and is continuing under the
                  Indenture,  the Company and the  Restricted  Subsidiaries will
                  not be subject to the provisions in Sections  4.13, 4.14, 4.15
                  and  4.16  of  the  Indenture  (collectively,  the  "Suspended
                  Covenants").  In the event that the Company and the Restricted
                  Subsidiaries are not  subject to  the  Suspended Covenants for
                  any period of time as a result of the preceding  sentence and,
                  subsequently, one or both of the Rating Agencies withdraws its
                  ratings or downgrades the ratings assigned to the  Notes below
                  the required Investment Grade Ratings so that the Notes do not
                  have an Investment Grade Rating from either Rating Agency,  or
                  a Default or Event of  Default occurs and is continuing,  then
                  the Company  and the  Restricted  Subsidiaries will thereafter
                  again be subject to the  Suspended  Covenants  and  compliance
                  with  the  Suspended  Covenants  with  respect  to  Restricted
                  Payments made after the time  of such  withdrawal,  downgrade,
                  Default or Event  of Default will  be calculated in accordance
                  with the  terms of  Section  4.14 as  though such covenant had
                  been in effect during the entire period  of time from the date
                  the Notes are issued; provided,  however,  that if at any time
                  the Notes  have an  Investment Grade  Rating  from both of the
                  Rating  Agencies  and  either  a   rating  of  Baa2   (or  the
                  equivalent) by Moody's or BBB (or the equivalent) by S&P, then
                  the  Company  and  the  Restricted  Subsidiaries will  not  be
                  subject to the Suspended Covenants  from and  after such time,
                  notwithstanding anything to the contrary in this Section 4.18,
                  and thereafter the  application of  the Suspended Covenants to
                  the  Company  and   the   Restricted   Subsidiaries  will   be
                  permanently terminated  and the Suspended Covenants will be of
                  no force and effect."








         Section 2.     Amendments to Third Supplemental Indenture.
                        ------------------------------------------

                  (a)  Section 4.18.  Section  4.18  of the  Third  Supplemental
Indenture is hereby amended to read in its entirety as follows:

                  "Section 4.18. Suspension or Elimination of Covenants.  During
                  any period of time that (a) the Notes have an Investment Grade
                  Rating from either of  the Rating Agencies and  (b) no Default
                  or Event of  Default has  occurred and is continuing under the
                  Indenture,  the Company and  the Restricted  Subsidiaries will
                  not be subject to the provisions in Sections  4.13, 4.14, 4.15
                  and  4.16  of  the  Indenture  (collectively,  the  "Suspended
                  Covenants").  In the event that the Company and the Restricted
                  Subsidiaries  are not  subject to  the Suspended Covenants for
                  any period of time as a result of the  preceding sentence and,
                  subsequently, one or both of the Rating Agencies withdraws its
                  ratings or downgrades the ratings assigned to the Notes below
                  the required Investment Grade Ratings so that the Notes do not
                  have an Investment Grade Rating from either Rating Agency,  or
                  a Default or Event of Default occurs  and is continuing,  then
                  the Company  and the  Restricted Subsidiaries  will thereafter
                  again be subject  to the  Suspended  Covenants and  compliance
                  with  the  Suspended  Covenants  with  respect  to  Restricted
                  Payments made after the time  of such  withdrawal,  downgrade,
                  Default or Event of  Default will  be calculated in accordance
                  with the  terms of  Section 4.14  as  though such covenant had
                  been in effect during the  entire period of time from the date
                  the Notes are issued; provided,  however,  that if at any time
                  the Notes  have an  Investment  Grade Rating  from both of the
                  Rating  Agencies   and  either  a  rating  of  Baa2   (or  the
                  equivalent) by Moody's or BBB (or the equivalent) by S&P, then
                  the  Company  and the  Restricted  Subsidiaries  will  not  be
                  subject to the Suspended  Covenants from and after  such time,
                  notwithstanding anything to the contrary in this Section 4.18,
                  and  thereafter the  application of the Suspended Covenants to
                  the  Company   and  the   Restricted   Subsidiaries   will  be
                  permanently terminated and the  Suspended Covenants will be of
                  no force and effect."

     Section 3. Ratification.  This Supplemental Indenture is executed and shall
be construed as an indenture  supplemental  to the Indenture and, as provided in
the Indenture, this Supplemental Indenture forms a part of the Indenture. Except
to the extent amended by or supplemented  by this  Supplemental  Indenture,  the
Company and the Trustee  hereby ratify,  confirm,  and reaffirm the Indenture in
all respects.

     Section 4. Counterparts. This Supplemental Indenture may be executed in any
number of counterparts,  each of which so executed shall be an original, but all
such counterparts shall together constitute but one and the same instrument.

     Section 5.  Governing  Law.  The laws of the State of New York shall govern
the construction and  interpretation  of this  Supplemental  Indenture,  without
regard to principles of conflicts of laws.

     Section 6. Trustee. The Trustee makes no representations as to the validity
or  sufficiency  of this  Supplemental  Indenture.  The recitals and  statements
herein are deemed to be those of the Company and not the Trustee.

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     IN WITNESS  WHEREOF,  the parties  hereto  have  caused  this  Supplemental
Indenture to be signed on their behalf by their duly authorized  representatives
as of the date first above written:

                               Pioneer Natural Resources Company



                               By:        /s/ Richard P. Dealy
                                    -------------------------------------------
                               Name:      Richard P. Dealy
                               Title:     Vice President and Chief Accounting
                                          Officer


                               The Bank of New York, as Trustee



                               By:        /s/ Remo J. Reale
                                    -------------------------------------------
                               Name:      Remo J. Reale
                               Title:     Vice President