EXHIBIT 32.1



                                CERTIFICATION OF
                             CHIEF EXECUTIVE OFFICER
                      OF PIONEER NATURAL RESOURCES COMPANY
                         PURSUANT TO 18 U.S.C. ss. 1350


     I, Scott D.  Sheffield,  Chairman  and Chief  Executive  Officer of Pioneer
Natural Resources Company (the "Company"),  hereby certify that the accompanying
Quarterly  Report on Form 10-Q for the quarterly period ended September 30, 2005
and filed with the Securities and Exchange  Commission pursuant to Section 13(a)
of the  Securities  Exchange  Act of 1934 (the  "Report")  by the Company  fully
complies with the requirements of that section.

     I further  certify  that the  information  contained  in the Report  fairly
presents,  in all material  respects,  the  financial  condition  and results of
operations of the Company.




                                             /s/ Scott D. Sheffield
                                            -----------------------------------
                                    Name:   Scott D. Sheffield, Chairman and
                                              Chief Executive Officer
                                    Date:   November 8, 2005