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.

November 6, 2006
                                        /s/ Scott D. Sheffield
                                      ---------------------------------
                                      Scott D. Sheffield, Chairman and
                                      Chief Executive Officer