FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person * BAROFFIO JAMES R   2. Issuer Name and Ticker or Trading Symbol PIONEER NATURAL RESOURCES CO [PXD] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 5205 N. O'CONNOR BLVD., SUITE 900 3. Date of Earliest Transaction (Month/Day/Year) 05/11/2006 (Street) IRVING, TX 75039 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 05/11/2006   M   10,000 A $ 10.25 11,912 D   Common Stock 05/11/2006   S   10,000 D $ 41.81 1,912 D   Common Stock 05/11/2006   M   1,978 A $ 13.5 13,031 I by Trust (1) Common Stock 05/11/2006   S   1,978 D $ 41.81 11,053 I by Trust (1)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Non-Qualified Stock Option (right to buy)

$ 10.25

05/11/2006

M

10,000

05/18/2001

05/18/2006

Common Stock

10,000

$ 10.25

10,000

D

Non-Qualified Stock Option (right to buy)

$ 13.5

05/11/2006

M

1,978

05/18/2001(2)

05/18/2006

Common Stock

1,978

$ 13.5

0

I

by Trust (1)

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
BAROFFIO JAMES R 5205 N. O'CONNOR BLVD., SUITE 900 IRVING, TX 75039	X

Signatures

By: Mark H. Kleinman, Attorney-in-Fact For: James R. Baroffio		05/12/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	Shares held by Baroffio Family Trust, of which James R. Baroffio is Trustee.
(2)	One-fourth of the options shall vest at the end of each of the Board's fiscal quarters (with the exception of the quarter ending with the Annual Meeting, which is deemed to end on the day prior to the Annual meeting), are immediately exercisable upon such vesting, and survive for a term of five years from the vest date.

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