UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549



                                    FORM 8-K

                                 CURRENT REPORT


     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

       Date of Report (Date of earliest event reported): December 20, 2001



                           PARKER & PARSLEY 91-B, L.P.
             (Exact name of Registrant as specified in its charter)




            Delaware                    33-38582-02          75-2397335
-----------------------------------    -------------    ---------------------
 (State or other jurisdiction of        Commission        (I.R.S. Employer
 incorporation or organization)         File Number     Identification Number)




5205 N. O'Connor Blvd., Suite 1400, Irving, Texas             75039
-------------------------------------------------          -----------
    (Address of principal executive offices)                (Zip code)



       Registrant's Telephone Number, including area code : (972) 444-9001


                                 Not applicable
              (Former name, former address and former fiscal year,
                         if changed since last report)



<PAGE>



                           Parker & Parsley 91-B, L.P.



Item 2.   Disposition of Assets

On December  20,  2001,  the limited  partners of the  registrant  approved  the
previously  announced  merger of the  registrant  with and into Pioneer  Natural
Resources USA, Inc.  ("Pioneer  USA"),  with Pioneer USA  surviving.  The merger
occurred on December 20, 2001. As a result of the merger,  the limited  partners
of the registrant  received  common stock,  par value $.01 per share, of Pioneer
Natural  Resources Company  ("Pioneer").  The terms and provisions of the merger
have been previously  reported in the proxy  statement/prospectus  dated October
12,  2001,  forming  a part of  Pioneer's  registration  statement  on Form  S-4
(Commission File No. 333-59094).


                                        2

<PAGE>




                               S I G N A T U R E S


Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.

                                   PARKER & PARSLEY 91-B, L.P.

                                   By:  Pioneer Natural Resources USA, Inc.
                                          Managing General Partner



Date:    December 21, 2001         By:          /s/ Rich Dealy
                                        ------------------------------------
                                        Rich Dealy
                                        Vice President and
                                        Chief Accounting Officer


                                        3

<PAGE>
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{"company-data": {"conformed-name": "PARKER & PARSLEY 91-B LP", "cik": "0000871367", "assigned-sic": "1311", "irs-number": "752397335", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "8-K", "act": "34", "file-number": "033-38582-02", "film-number": "1820399"}, "business-address": {"street1": "303 W WALL STE 101", "city": "MIDLAND", "state": "TX", "zip": "79701", "phone": "9156834768"}}
UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                                    FORM 8-K

                                 CURRENT REPORT

     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

       Date of Report (Date of earliest event reported): December 20, 2001

                           PARKER & PARSLEY 91-B, L.P.
             (Exact name of Registrant as specified in its charter)

            Delaware                    33-38582-02          75-2397335
-----------------------------------    -------------    ---------------------
 (State or other jurisdiction of        Commission        (I.R.S. Employer
 incorporation or organization)         File Number     Identification Number)

5205 N. O'Connor Blvd., Suite 1400, Irving, Texas             75039
-------------------------------------------------          -----------
    (Address of principal executive offices)                (Zip code)

       Registrant's Telephone Number, including area code : (972) 444-9001

                                 Not applicable
              (Former name, former address and former fiscal year,
                         if changed since last report)
Parker & Parsley 91-B, L.P.

Item 2.   Disposition of Assets

On December  20,  2001,  the limited  partners of the  registrant  approved  the
previously  announced  merger of the  registrant  with and into Pioneer  Natural
Resources USA, Inc.  ("Pioneer  USA"),  with Pioneer USA  surviving.  The merger
occurred on December 20, 2001. As a result of the merger,  the limited  partners
of the registrant  received  common stock,  par value $.01 per share, of Pioneer
Natural  Resources Company  ("Pioneer").  The terms and provisions of the merger
have been previously  reported in the proxy  statement/prospectus  dated October
12,  2001,  forming  a part of  Pioneer's  registration  statement  on Form  S-4
(Commission File No. 333-59094).

                                        2
S I G N A T U R E S

Pursuant  to the  requirements  of the  Securities  Exchange  Act of  1934,  the
Registrant  has duly  caused  this  report  to be  signed  on its  behalf by the
undersigned hereunto duly authorized.

                                   PARKER & PARSLEY 91-B, L.P.

                                   By:  Pioneer Natural Resources USA, Inc.
                                          Managing General Partner

Date:    December 21, 2001         By:          /s/ Rich Dealy
                                        ------------------------------------
                                        Rich Dealy
                                        Vice President and
                                        Chief Accounting Officer

                                        3