UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549
                               ------------------


                                   FORM 8-A/A
                                (Amendment No. 1)


                FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES
                     PURSUANT TO SECTION 12(b) OR (g) OF THE
                         SECURITIES EXCHANGE ACT OF 1934

                               -------------------


                        PIONEER NATURAL RESOURCES COMPANY
             (Exact name of registrant as specified in its charter)


                 Delaware                               75-2702753
 (State of incorporation or organization)            (I.R.S. Employer
                                                  Identification Number)

      5205 N. O'Connor Blvd., Suite 900
                Irving, Texas                              75039
  (Address of principal executive offices)               (Zip Code)

         Securities to be registered pursuant to Section 12(b) of the Act:

           Title of each class                Name of each exchange on which
           to be so registered                each class is to be registered
           -------------------                ------------------------------

   Rights to Purchase Series A Junior
   Participating Preferred Stock, par
   value $.01 per share                          New York Stock Exchange

     If this form relates to the registration of a class of securities  pursuant
to  Section  12(b) of the  Exchange  Act and is  effective  pursuant  to General
Instruction A.(c), please check the following box. |X|

     If this form relates to the registration of a class of securities  pursuant
to  Section  12(g) of the  Exchange  Act and is  effective  pursuant  to General
Instruction A.(d), please check the following box. |_|

     Securities  Act  registration  statement  file  number  to which  this form
relates (if applicable): N/A

     Securities to be registered pursuant to Section 12(g) of the Act: None







     This  Amendment  No. 1 to Form 8-A amends Items 1 and 2 of Pioneer  Natural
Resources  Company's (the  "Company")  Registration  Statement on Form 8-A filed
with the  Securities  and Exchange  Commission  on July 24, 2001, to disclose an
amendment to the Rights  Agreement,  dated as of July 20, 2001 (as amended,  the
"Rights Agreement"),  between the Company and Continental Stock Transfer & Trust
Company,  as Rights Agent (the "Rights Agent"). On May 22, 2006, the Company and
the Rights  Agent  entered  into an  Amendment  No. 1 to Rights  Agreement  (the
"Amendment")  to, among other things,  (1) increase the trigger under the Rights
Agreement  from 15% to 20%,  (2) delete  language in the Rights  Agreement  that
grandfathered  Southeastern  Asset  Management,  Inc.  ("SEAM") under the Rights
Agreement so that SEAM's then approximate 27% ownership in the Company would not
result  in SEAM  being  regarded  as an  "Acquiring  Person"  under  the  Rights
Agreement, and (3) effect other technical modifications.

Item 1.     Description of Registrant's Securities to be Registered.

     On July 19, 2001, the board of directors of the Company declared a dividend
of one preferred share purchase right (a "Right") for each outstanding  share of
common  stock,  par value  $0.01 per share  (the  "Common  Shares"  or  "Capital
Stock"),  of the  Company.  The  dividend was paid on July 31, 2001 (the "Record
Date") to the  holders  of  Capital  Stock of record on that  date.  Each  Right
entitles the registered  holder to purchase from the Company one  one-thousandth
of a share of Series A Junior Participating Preferred Stock, par value $0.01 per
share  (the  "Preferred  Shares"),  of the  Company at a price of $95.00 per one
one-thousandth  of  a  Preferred  Share  (the  "Purchase  Price"),   subject  to
adjustment.  The description and terms of the Rights are set forth in the Rights
Agreement.

     Until the earlier to occur of (i) the tenth business day following a public
announcement that a person has acquired  beneficial  ownership of 20% or more of
the outstanding Capital Stock (an "Acquiring Person") or (ii) the tenth business
day (subject to extension) after a person commences,  or announces its intention
to commence,  a tender offer or exchange offer the  consummation  of which would
result in any  person  becoming  the  beneficial  owner of the  number of shares
necessary to be an Acquiring  Person (the earlier of such dates being called the
"Distribution  Date"), the Rights will be evidenced,  with respect to any of the
Common Share  certificates  outstanding  as of the Record  Date,  by such Common
Share  certificates with a copy of this Summary of Rights attached thereto.  The
Rights Agreement  provides that, until the Distribution Date, the Rights will be
transferred with and only with the Capital Stock.  Until the  Distribution  Date
(or  earlier  redemption  or  expiration  of  the  Rights),  new  Capital  Stock
certificates  issued  after the Record  Date,  upon  transfer or new issuance of
Capital  Stock will  contain a notation  incorporating  the Rights  Agreement by
reference.  Until the Distribution Date (or earlier  redemption or expiration of
the Rights),  the surrender for transfer of any  certificates for Capital Stock,
outstanding as of the Record Date,  even without such notation or a copy of this
Summary of Rights being attached  thereto,  will also constitute the transfer of
the Rights associated with the Capital Stock represented by such
certificate.

     As  soon  as  practicable   following  the  Distribution   Date,   separate
certificates  evidencing  the Rights  ("Right  Certificates")  will be mailed to
holders  of  record of the  Capital  Stock as of the  close of  business  on the
Distribution Date and such separate Right  Certificates  alone will evidence the
Rights.

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     The Rights are not exercisable until the Distribution Date. The Rights will
expire  on July 31,  2011  (the  "Final  Expiration  Date"),  unless  the  Final
Expiration  Date is extended  or unless the Rights are  earlier  redeemed by the
Company, in each case, as described below.

     The Purchase  Price  payable,  and the number of Preferred  Shares or other
securities  or  property  issuable,  upon  exercise of the Rights are subject to
adjustment  from time to time to  prevent  dilution  (i) in the event of a stock
dividend on, or a subdivision, combination or reclassification of, the Preferred
Shares, (ii) upon the grant to holders of the Preferred Shares of certain rights
or  warrants  to  subscribe  for or  purchase  Preferred  Shares at a price,  or
securities  convertible into Preferred Shares with a conversion price, less than
the  then  current  market  price of the  Preferred  Shares  or  (iii)  upon the
distribution to holders of the Preferred  Shares of evidences of indebtedness or
assets  (excluding  regular  periodic  cash  dividends  paid out of  earnings or
retained  earnings or dividends  payable in Preferred Shares) or of subscription
rights or warrants (other than those referred to above).

     The number of outstanding Rights and the number of one one-thousandths of a
Preferred  Share  issuable  upon  exercise  of each  Right are also  subject  to
adjustment  in the  event  of a stock  split  of the  Common  Shares  or a stock
dividend  on the  Common  Shares  payable  in  Common  Shares  or  subdivisions,
consolidations or combinations of the Common Shares occurring, in any such case,
prior to the Distribution Date.

     Preferred   Shares   purchasable  upon  exercise  of  the  Rights  are  not
redeemable.  Each  Preferred  Share will be entitled  to a minimum  preferential
quarterly  dividend  payment  of $1.00  per  share  but will be  entitled  to an
aggregate dividend of 1,000 times the dividend declared per Common Share. In the
event of liquidation,  the holders of the Preferred Shares will be entitled to a
minimum  preferential  liquidation  payment  of $1,000  per share plus an amount
equal to  accrued  and  unpaid  dividends  thereon  but will be  entitled  to an
aggregate  payment  of 1,000  times the  payment  made per  Common  Share.  Each
Preferred  Share will have 1,000 votes,  voting together with the Common Shares.
Finally, in the event of any merger, consolidation or other transaction in which
Common Shares are exchanged,  each  Preferred  Share will be entitled to receive
1,000 times the amount received per Common Share.  These rights are protected by
customary antidilution provisions.

     Because of the nature of the Preferred  Shares'  dividend,  liquidation and
voting rights, the value of the one one-thousandth interest in a Preferred Share
purchasable  upon  exercise of each Right  should  approximate  the value of one
Common Share.

     In the  event  that,  after a person or a group  has  become  an  Acquiring
Person,  the  Company  is  acquired  in a merger or other  business  combination
transaction or 50% or more of its consolidated  assets or earning power are sold
or transferred (subject to certain exceptions), proper provision will be made so
that each holder of a Right will thereafter have the right to receive,  upon the
exercise thereof at the then current exercise price of the Right, that number of
shares  of  common  stock  of the  acquiring  company  which at the time of such
transaction  will have a market  value of two times  the  exercise  price of the
Right.  In the  event  that any  person  becomes  an  Acquiring  Person,  proper
provision  shall be made so that  each  holder  of a Right,  other  than  Rights
beneficially owned by the Acquiring Person (which will thereafter be void), will

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thereafter  have the right to receive upon exercise that number of Common Shares
having a market value of two times the exercise price of the Right.

     At any time  after a person or group has  become an  Acquiring  Person  and
prior  to the  acquisition  by  such  person  or  group  of 50% or  more  of the
outstanding  Capital  Stock,  the board of directors of the Company may exchange
the Rights  (other than  Rights  owned by such person or group which have become
void),  in whole or in part,  at an exchange  ratio of one Common Share for each
two  Common  Shares for which each  Right is then  exercisable  pursuant  to the
provisions of the Rights Agreement (subject to adjustment).

     With  certain  exceptions,  no  adjustment  in the  Purchase  Price will be
required until  cumulative  adjustments  require an adjustment of at least 1% of
such Purchase Price. No fractional  Preferred  Shares will be issued (other than
fractions  which are  integral  multiples of one  one-thousandth  of a Preferred
Share,  which may, at the  election of the Company,  be evidenced by  depositary
receipts) and in lieu  thereof,  an adjustment in cash will be made based on the
market price of the  Preferred  Shares on the last trading day prior to the date
of exercise.

     At any time prior to such time as a person or group  becomes  an  Acquiring
Person,  the board of  directors  of the Company may redeem the Rights in whole,
but not in part,  at a price of $0.001 per Right (with respect to each holder of
Rights,  rounded up to the nearest  cent for the  aggregate  Rights held by such
holder)  (the  "Redemption  Price").  The  redemption  of the Rights may be made
effective  at such time on such basis and with such  conditions  as the board of
directors of the Company in its sole discretion may establish.  Immediately upon
any  redemption of the Rights,  the right to exercise the Rights will  terminate
and the only right of the holders of Rights  will be to receive  the  Redemption
Price.

     The terms of the Rights may be  amended  by the board of  directors  of the
Company without the consent of the holders of the Rights, including an amendment
to lower certain thresholds  described above to not less than the greater of (i)
the sum of .001% and the largest  percentage  of the  outstanding  Capital Stock
then  known to the  Company to be  beneficially  owned by any person or group of
affiliated or associated  persons (subject to certain  exceptions) and (ii) 10%,
except  that from and after  such time as any person or group of  affiliated  or
associated  persons becomes an Acquiring  Person no such amendment may adversely
affect the interests of the holders of the Rights.

     Until a Right is  exercised,  the  holder  thereof,  as such,  will have no
rights  as a  stockholder  of the  Company,  including  the  right to vote or to
receive dividends.

     A copy of the Rights Agreement was filed as exhibit 4.1 to the Registration
Statement on Form 8-A filed with the Securities and Exchange  Commission on July
24, 2001. This summary description of the Rights does not purport to be complete
and is qualified in its entirety by reference to the Rights Agreement.

Item 2.  Exhibits.

4.1  Rights  Agreement,  dated as of July 20,  2001,  between  the  Company  and
     Continental Stock Transfer & Trust Company, as Rights Agent, specifying the
     terms of the Rights,  which includes the form of Certificate of Designation

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     of Series A Junior Participating  Preferred Stock as Exhibit A, the form of
     Right  Certificate  as  Exhibit B and the form of the  Summary of Rights to
     Purchase  Preferred  Shares as Exhibit C.  (Incorporated  by  reference  to
     Exhibit 4.1 to the Company's  Registration Statement on Form 8-A filed with
     the Securities and Exchange Commission on July 24, 2001.)

4.2  Amendment No. 1 to Rights Agreement, dated as of July 20, 2001, between the
     Company and Continental Stock Transfer & Trust Company, as Rights Agent.*

--------------
*  Filed herewith.


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                                    SIGNATURE

     Pursuant to the  requirements of Section 12 of the Securities  Exchange Act
of 1934, the registrant has duly caused this registration statement to be signed
on its behalf by the undersigned, thereto duly authorized.


                                 PIONEER NATURAL RESOURCES COMPANY


Date:  May 22, 2006              By: /s/ Darin G. Holderness
                                     ---------------------------------------
                                     Darin G. Holderness
                                     Vice President and Chief Accounting Officer


                                      S-1







                                  EXHIBIT INDEX


4.1  Rights  Agreement,  dated as of July 20,  2001,  between  the  Company  and
     Continental Stock Transfer & Trust Company, as Rights Agent, specifying the
     terms of the Rights,  which includes the form of Certificate of Designation
     of Series A Junior Participating  Preferred Stock as Exhibit A, the form of
     Right  Certificate  as  Exhibit B and the form of the  Summary of Rights to
     Purchase  Preferred  Shares as Exhibit C.  (Incorporated  by  reference  to
     Exhibit 4.1 to the Company's  Registration Statement on Form 8-A filed with
     the Securities and Exchange Commission on July 24, 2001.)

4.2  Amendment No. 1 to Rights Agreement, dated as of July 20, 2001, between the
     Company and Continental Stock Transfer & Trust Company, as Rights Agent.*

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*  Filed herewith.