EXHIBIT 31.1

                      CHIEF EXECUTIVE OFFICER CERTIFICATION

     I, Scott D. Sheffield, certify that:

     1.     I have  reviewed  this  quarterly  report on  Form 10-Q  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.

May 9, 2006
                                        /s/ Scott D. Sheffield
                                        --------------------------------
                                        Scott D. Sheffield, Chairman and
                                        Chief Executive Officer