EXHIBIT 31.1

                      CHIEF EXECUTIVE OFFICER CERTIFICATION

     I, Scott D. Sheffield, certify that:

     1.     I have reviewed this  annual report on  Form 10-K of Pioneer Natural
            Resources Company;

     2.     Based on my  knowledge,  this  report does  not  contain any  untrue
            statement  of a  material  fact or  omit to  state a  material  fact
            necessary to  make the  statements made,  in light  of circumstances
            under which such  statements were made,  not misleading with respect
            to the period covered by this report;

     3.     Based on my knowledge, the financial statements, and other financial
            information included in this  report, fairly present in all material
            respects the  financial condition,  results of  operations  and cash
            flows of  the registrant as of,  and for,  the periods  presented in
            this report;

     4.     The registrant's  other certifying officer and I are responsible for
            establishing and maintaining  disclosure controls and procedures (as
            defined in Exchange Act Rules 13a-15(e)  and 15d-15(e)) and internal
            control over  financial reporting (as defined in  Exchange Act Rules
            13a-15(f) and 15d-15(f)) for the registrant and have:

            (a)   Designed such  disclosure controls and  procedures, or  caused
                  such disclosure controls  and procedures to  be designed under
                  our supervision,  to ensure that material information relating
                  to the registrant, including its consolidated subsidiaries, is
                  made known to us by others within those entities, particularly
                  during the period in which this report is being prepared;

            (b)   Designed such  internal control over  financial reporting,  or
                  caused such internal  control over  financial  reporting to be
                  designed  under  our  supervision,   to   provide   reasonable
                  assurance regarding the reliability of financial reporting and
                  the preparation of financial  statements for external purposes
                  in accordance with generally accepted accounting principles;

            (c)   Evaluated  the  effectiveness of the  registrant's  disclosure
                  controls  and  procedures  and  presented  in  this report our
                  conclusions about the effectiveness of the disclosure controls
                  and procedures, as of the  end of  the period  covered by this
                  report based on such evaluation; and

            (d)   Disclosed  in  this  report  any  change  in  the registrant's
                  internal control over financial reporting that occurred during
                  the registrant's most recent fiscal quarter  (the registrant's
                  fourth fiscal  quarter in the case  of an annual report)  that
                  has materially affected, or is reasonably likely to materially
                  affect,  the  registrant's  internal  control  over  financial
                  reporting; and

     5.     The registrant's  other  certifying  officer and  I have  disclosed,
            based  on  our  most  recent  evaluation of  internal  control  over
            financial  reporting,  to the  registrant's  auditors and  the audit
            committee  of  the  registrant's  board  of  directors  (or  persons
            performing the equivalent functions):

            (a)   All significant  deficiencies and  material  weaknesses in the
                  design  or   operation  of  internal  control  over  financial
                  reporting which are  reasonably likely to adversely affect the
                  registrant's ability to record,  process, summarize and report
                  financial information; and

            (b)   Any fraud,  whether or not material,  that involves management
                  or  other  employees  who  have  a  significant  role  in  the
                  registrant's internal control over financial reporting.

February 16, 2005
                               /s/ Scott D. Sheffield
                             ------------------------------------------
                             Scott D. Sheffield, Chairman and
                             Chief Executive Officer