EXHIBIT 4.2

                          FOURTH SUPPLEMENTAL INDENTURE

     THIS FOURTH  SUPPLEMENTAL  INDENTURE  dated as of September  30, 2004 (this
"Supplemental  Indenture"),  is  entered  into  by  and  among  Pioneer  Natural
Resources  Company, a Delaware  corporation (the "Company"),  and Wachovia Bank,
National  Association,  the successor to First Union  National  Bank, a national
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. Pursuant to the terms of that certain Agreement and Plan of Merger dated
as of September  29, 2004, by and between the Company and Pioneer Debt Sub, LLC,
a Texas limited liability  company and a wholly-owned  subsidiary of the Company
("Debt Sub"), Debt Sub has merged with and into the Company, with the Company as
the surviving corporation (the "Merger").

     B. Pursuant to Article VII of that certain  Indenture  dated as of December
18,  2001,  by and among Debt Sub,  the Company  and the Trustee (as  heretofore
amended and supplemented, the "Indenture"), upon consummation of the Merger, the
Company  shall  expressly  assume,  by  supplemental  indenture,   executed  and
delivered to the Trustee all obligations of Debt Sub under the Indenture and the
4.75% Senior Convertible Notes due 2021 issued thereunder (the "Securities") and
the Company will  succeed to, and be  substituted  for,  and may exercise  every
right and power of Debt Sub under the Indenture and the Securities.

     C. In accordance with Section 11.1(a) of the Indenture, the Company and the
Trustee are  authorized  to execute and deliver this  Supplemental  Indenture to
amend  the  Indenture  to  provide  for the  assumption  by the  Company  of the
obligations of Debt Sub under the Indenture and the Securities without notice to
or the consent of any Securityholder.

     D. 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 to provide for the  assumption  by the Company of the  obligations  of
Debt Sub under the Indenture and the Securities.

     E. The Company  has duly  authorized  the  execution  and  delivery of this
Supplemental Indenture.

                                   AGREEMENTS

     NOW,  THEREFORE,  in  consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the Company
and the Trustee mutually covenant and agree for the equal and ratable benefit of
the Holders of the Securities as follows:







     Section 1.  Confirmation  of  Original  Indenture.  Except as  amended  and
supplemented hereby, the Indenture is hereby ratified,  confirmed and reaffirmed
in all respects.  The Indenture and this  Supplemental  Indenture shall be read,
taken and construed as one and the same instrument.

     Section 2. Successor Company Substituted. In accordance with Article VII of
the Indenture,  upon  consummation of the Merger,  the Company shall succeed to,
and be  substituted  for,  and may  exercise  every right and power of, Debt Sub
under the  Securities  and the Indenture  with the same effect as if the Company
had been named therein as Debt Sub.

     Section 3. Assumption of Obligations.  Upon consummation of the Merger, the
Company  hereby  assumes all of the  obligations of Debt Sub under the Indenture
and the Securities with the same effect as if the Company had been named therein
as Debt Sub.

     Section 4. Miscellaneous.

            (a) Execution of Supplemental Indenture. 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.

            (b) NEW YORK LAW TO GOVERN.  THE INTERNAL  LAW OF  THE STATE  OF NEW
YORK SHALL  GOVERN  AND BE USED TO  CONSTRUE  THIS  SUPPLEMENTAL  INDENTURE  BUT
WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT
THAT THE  APPLICATION  OF THE LAWS OF  ANOTHER  JURISDICTION  WOULD BE  REQUIRED
THEREBY.

            (c) Counterparts.  The parties may sign any number of copies of this
Supplemental  Indenture.  Each signed copy shall be an original, but all of them
together represent the same agreement.

            (d) Effect  of  Headings.  The  Section  headings   herein  are  for
convenience only and shall not affect the construction hereof.

            (e) The Trustee.  The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals  contained  herein,  all of which
recitals are made solely by the Company.

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                                       2







     IN WITNESS  WHEREOF,  the parties  hereto  have  caused  this  Supplemental
Indenture to be duly executed as of the date first above written.

          Dated:  September 30, 2004

                                          PIONEER NATURAL RESOURCES COMPANY

                                          By:   /s/ Richard P. Dealy
                                                -------------------------------
                                                Name:  Richard P. Dealy
                                                Title:  Vice President



                                          WACHOVIA BANK, NATIONAL ASSOCIATION,
                                          as Trustee

                                          By:   /s/ Doug Milner
                                                -------------------------------
                                                Authorized Signatory


               Signature Page to the Fourth Supplemental Indenture
                        (4.75% Senior Convertible Notes)