UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C.  20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

AMENDMENT NO. 6

Southwest Royalties Institutional Income Fund X-B, L.P.

(Name of Issuer)

Limited Partnership Interests

(Title of Class of Securities)

Not Applicable

(CUSIP Number)

L. Paul Latham

Clayton Williams Energy, Inc.

6 Desta Drive, Suite 6500

Midland, Texas 79705-5510

(432) 682-6324

(Name, Address and Telephone Number of Person

Authorized to Receive Notices and Communications)

June 16, 2009

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box:  □

CUSIP No. Not Applicable

(1)	Names of Reporting Persons	Clayton Williams Energy, Inc.
(2)	Check the Appropriate Box	(a)
	if a Member of a Group	(b)           x
(3)	SEC Use Only
(4)	Source of Funds	AF
(5)	Check if Disclosure of Legal
	Proceedings is Required
	Pursuant to Items 2(d) or 2(e)	Not Applicable
(6)	Citizenship or Place of
	Organization	Delaware corporation
Number of Shares/Units Beneficially Owned by Each Reporting Person With:
(7)	Sole Voting Power	1,924.8 Units
(8)	Share Voting Power	None
(9)	Sole Dispositive Power	1,924.8 Units
(10)	Shared Dispositive Power	None
(11)	Aggregate Amount Beneficially
	Owned by Each Reporting Person	1,924.8 Units
(12)	Check if the Aggregate Amount in
	Row (11) Excludes Certain Shares	Not Applicable
(13)	Percent of Class Represented
	by Amount in Row (11)	17.2% of class of
		11,181 Units
(14)	Type of Reporting Person	HC (sole parent company of the Managing
		General Partner of Issuer)

Item 1.	Type of Security:	Limited Partnership Interests ("Units")
	Name of Issuer:	Southwest Royalties
		Institutional Income X-B, L.P.
	Address of Issuer's Principal	6 Desta Drive, Suite 6500
	Executive Offices:	Midland, Texas 79705
Item 2(a).	Name of Person Filing:	Clayton Williams Energy, Inc.
Item 2(b).	Address of Principal	6 Desta Drive, Suite 6500
	Business Office:	Midland, Texas 79705
Item 2(c).	Present Occupation:	Not Applicable
Item 2(d).	Criminal Convictions:	None
Item 2(e).	Civil Securities Laws Injunctions
	or Prohibitions:	None
Item 2(f).	Citizenship:	Delaware, U.S.A.
Item 3.	Source of Funds:
	Southwest Royalties, Inc., as Managing General Partner of the Issuer, used its working capital to acquire Units (see Item 4). As sole stockholder of Southwest Royalties, Inc., the Reporting Person owns an indirect interest in the Units acquired by Southwest Royalties, Inc.
Item 4.	Purpose of Transactions:
	Southwest Royalties, Inc. satisfied the requirements of the Right of Presentment contained in the Issuer's Agreement of Limited Partnership whereby Southwest Royalties, Inc., as Managing General Partner, agrees to acquire Units from limited partners seeking an exit from the Issuer at a formula price. The Reporting Person, as sole stockholder of Southwest Royalties, Inc., owns an indirect interest in the Units acquired.

Item 5.	Interest in Securities:
	Southwest Royalties, Inc., which is the Managing General Partner of the Issuer, holds a total of 1,924.8 Units of limited partnership interests over which it has sole voting and dispositive powers. As the sole stockholder of Southwest Royalties, Inc., the Reporting Person holds an indirect interest of 1,924.8 limited partnership Units.  These Units represent 17.2% of the total 11,181 Units, which are issued and outstanding. The purchase transactions, which resulted in the indirect ownership of the Reporting Person increasing from 16.6% to 17.2%, occurred between October 1, 2008 and June 15, 2009 when the Managing General Partner purchased an additional 65 Units as part of the Issuer's Right of Presentment program. The price per unit ranged from $79.50 to $286.14.
Item 6.	Contracts, Arrangements, Undertakings
	or Relationships with Respect
	to Securities of the Issuer:	Not Applicable
Item 7.	Material to Be Filed as Exhibits:	Not Applicable

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Date: June 23, 2009	By:	/s/ L. Paul Latham
		L. Paul Latham, President and
		Chief Executive Officer,
		of Southwest Royalties, Inc.
		the Managing General Partner