1
                                                                    EXHIBIT 23.6

                CONSENT OF INDEPENDENT ENGINEERS AND GEOLOGISTS

Williamson Petroleum Consultants, Inc. (Williamson) hereby consents to the
incorporation by reference to our report entitled "Evaluation and Review of Oil
and Gas Reserves to the Interests of Mesa Inc. in the Hugoton Area, Various
Counties, Kansas and West Panhandle Area, Various Counties, Texas, Effective
December 31, 1996, for Disclosure to the Securities and Exchange Commission,
Williamson Project 6.8421" dated March 17, 1997, with respect to Mesa Inc. and
to all references to our firm included in or made a part of the Pioneer Natural
Resources Company and Pioneer Natural Resources USA, Inc. Amendment No. 1 to the
Registration Statement on Form S-3 to be filed on or before January 5, 1998.


                                      /s/ Williamson Petroleum Consultants, Inc.
                                      ------------------------------------------
                                          WILLIAMSON PETROLEUM CONSULTANTS, INC.

Houston, Texas
December 31, 1997