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
Annual  Report on Form 10-K for the year ended  December 31, 2006 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.

                              Name:  /s/ Scott D. Sheffield
                                     -----------------------------------------
                                     Scott D. Sheffield, Chairman of the Board
                                     and Chief Executive Officer

                              Date:  February 19, 2007