ASSIGNMENT AND ASSUMPTION AGREEMENT

THIS ASSIGNMENT AND ASSUMPTION AGREEMENT (this “ Agreement ”), executed on March 13, 2009, to be effective as of 12:01 a.m. (Central Time) on April 15, 2009 (the “ Effective Time ”), is entered into by and among Lariat Services, Inc., a Texas corporation (“ LARIAT ”), and Clayton Williams Energy, Inc., a Delaware corporation (“ CWEI ”).  The parties to this Agreement are collectively referred to herein as the “ Parties ,” or individually as a “ Party .”

WHEREAS, each of LARIAT and CWEI holds a 49.5% limited partnership interest (the “ LP Interest ”) in Larclay, L.P., a Texas limited partnership (“ LARCLAY ”);

WHEREAS, each of LARIAT and CWEI holds a 50% membership interest (the “ LLC Interest ” and, together with the LP Interest, the “ Interests ”) in Larclay GP, LLC, a Texas limited liability company (“ GP ”);

WHEREAS, pursuant to loans made by LARIAT to LARCLAY, there are (a) a Promissory Note, dated March 31, 2008, in the principal amount of $2,500,000 payable by LARCLAY to LARIAT (the “ March 2008 Note ”) and (b) a Revolving Promissory Note, dated June 10, 2008, in the principal amount of $5,000,000 payable by LARCLAY to LARIAT (together with the March 2008 Note, the “ Notes ”);

WHEREAS, in connection with LARCLAY’s ownership and operation of its fleet of drilling rigs, LARIAT is a party to (a) Operating Agreement for Drilling Rigs dated April 20, 2006, between LARCLAY and LARIAT (the “ Operating Agreement ”) and (b) Consent and Agreement dated April 21, 2006, among LARCLAY, CWEI, LARIAT and Merrill Lynch Capital (collectively with the Operating Agreement, the “ Ancillary Agreements ”);

WHEREAS, LARIAT desires to transfer to CWEI, and CWEI desires to accept from LARIAT, the Interests, the Notes and the Ancillary Agreements; and

WHEREAS, the Agreement of Limited Partnership of LARCLAY and the Limited Liability Company Agreement of GP will be amended to the extent necessary to reflect the applicable matters set forth above and as contained in this Agreement.

NOW, THEREFORE, in consideration of the mutual covenants contained herein and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the Parties agree as follows:

Section 1.1                    Assignment of Interests, Notes and Ancillary Agreements .  Effective as of the Effective Time, LARIAT hereby assigns, transfers, sets over and delivers to

CWEI all of LARIAT’s right, title and interest in and to the Interests, the Notes and the Ancillary Agreements, and CWEI hereby accepts LARIAT’s right, title and interest in and to the Interests, the Notes and the Ancillary Agreements, provided, however, that LARIAT shall retain the right to all amounts owed by LARCLAY to LARIAT under the Operating Agreement as of the Effective Time.

Section 1.2                    Assumption of Obligations and Liabilities and Operatorship .  CWEI hereby assumes and agrees to timely and fully perform and discharge all duties, obligations and liabilities arising from or related to and whether arising or attributable to periods at, before or after the Effective Time: (a) being Operator under the Operating Agreement, (b) operations of drilling rigs and other services performed for LARCLAY or its affiliates, (c) the Ancillary Agreements, (d) LARIAT’s ownership of the Interests and the Notes and (e) the transactions hereunder or contemplated hereby (collectively, the “ Assumed Obligations ”).

Section 1.3                    Waiver of Claims .  Except as otherwise expressly provided in this Agreement, CWEI hereby expressly disclaims and waives any and all claims it may have against LARIAT in connection with the Assumed Obligations. Except as otherwise expressly provided in this Agreement and except for accounts payable to LARIAT for ordinary course of business services, LARIAT hereby expressly disclaims and waives any and all claims it may have against CWEI in connection with LARIAT’s ownership of the Interests, the Operating Agreement and the Ancillary Agreements.

Section 1.4                    Transfer of Equipment .  To the extent that, pursuant to the Operating Agreement, equipment owned by LARCLAY is in the possession of LARIAT as of the Effective Time, CWEI will, at its own expense, retrieve such equipment from LARIAT no later than May 31, 2009.  Notwithstanding that equipment owned by LARCLAY may be in the possession of LARIAT on or after the Effective Time, LARIAT shall not be required to maintain insurance coverage for such equipment after the Effective Time.  CWEI shall reimburse LARIAT for all storage costs incurred by LARIAT until the time such equipment is retrieved by CWEI.

Section 2.1                    Representations and Warranties of LARIAT . LARIAT represents and warrants to CWEI as follows:

(a)            Organization, Good Standing and Authority .  LARIAT is a corporation duly formed, validly existing and in good standing under the laws of the State of Texas.  The execution and delivery of this Agreement and the consummation by LARIAT of the transactions contemplated herein have been duly and validly authorized by all necessary corporate action by LARIAT.  This Agreement has been duly executed and delivered by LARIAT.  LARIAT has all

requisite corporate power and authority to enter into and perform this Agreement, to perform its obligations hereunder and to carry out the transactions contemplated herein.

(b)            Enforceability .   This Agreement constitutes a valid and binding obligation of LARIAT, enforceable against it in accordance with its terms, subject to applicable bankruptcy, insolvency, reorganization, moratorium and other similar laws affecting creditors’ rights generally and general principles of equity.

(c)            Title.   Except as contemplated by this Agreement, LARIAT has not taken any action to sell or encumber the Interests.

Section 2.2                    Representations and Warranties of CWEI . CWEI represents and warrants to LARIAT as follows:

(a)            Organization, Good Standing and Authority .   CWEI is a corporation duly formed, validly existing and in good standing under the laws of the State of Delaware.  The execution and delivery of this Agreement and the consummation by CWEI of the transactions contemplated herein have been duly and validly authorized by all necessary corporate action by CWEI.  This Agreement has been duly executed and delivered by CWEI.  CWEI has all requisite corporate power and authority to enter into and perform this Agreement, to perform its obligations hereunder and to carry out the transactions contemplated herein.

(b)            Enforceability .   This Agreement constitutes a valid and binding obligation of CWEI, enforceable against it in accordance with its terms, subject to applicable bankruptcy, insolvency, reorganization, moratorium and other similar laws affecting creditors’ rights generally and general principles of equity.

Section 2.3                    Survival .  All representations, warranties, covenants and indemnities made by the Parties in this Agreement or pursuant hereto shall survive the consummation of the transactions contemplated hereby.

Section 2.4                    Disclaimer of Representations and Warranties

(a)           THE PARTIES ACKNOWLEDGE AND AGREE THAT NONE OF THE PARTIES HAS MADE, DOES NOT MAKE, AND EACH SUCH PARTY SPECIFICALLY NEGATES AND DISCLAIMS, ANY REPRESENTATIONS, WARRANTIES, PROMISES, COVENANTS, AGREEMENTS OR GUARANTIES OF ANY KIND OR CHARACTER WHATSOEVER, WHETHER EXPRESS, IMPLIED OR STATUTORY, ORAL OR WRITTEN, PAST OR PRESENT, OTHER THAN THOSE INCLUDED IN THIS AGREEMENT.  THE PROVISIONS OF THIS SECTION HAVE BEEN NEGOTIATED BY THE PARTIES AFTER DUE CONSIDERATION AND ARE INTENDED TO BE A COMPLETE EXCLUSION AND NEGATION OF ANY REPRESENTATIONS OR WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, THAT MAY ARISE PURSUANT TO ANY LAW NOW OR HEREAFTER IN EFFECT, OR OTHERWISE, EXCEPT AS SET FORTH IN THIS AGREEMENT OR ANY OTHER DOCUMENT EXECUTED OR DELIVERED IN CONNECTION WITH THIS AGREEMENT.

(b)           Each of the Parties agrees that the disclaimers contained in this Section 2.4 are “conspicuous” disclaimers.  Any covenants implied by statute or law by the use of the words “grant,” “convey,” “bargain,” “sell,” “assign,” “transfer,” “deliver,” or “set over” or any of them or any other words used in this Agreement or any exhibits hereto are hereby expressly disclaimed, waived or negated.

Section 3.1                   Indemnification by LARIAT .   LARIAT shall defend, indemnify and hold harmless CWEI and its affiliates, and all of its and their directors, officers, employees, contractors, agents, and representatives (the “ CWEI Indemnitees ”) from and against any and all Losses asserted against, resulting from, imposed upon or incurred by any of the CWEI Indemnitees as a result of or arising out of the breach of any of the representations or warranties under Section 2.1 of this Agreement or any breach by LARIAT of any of its covenants in this Agreement.  “ Loss ” or “ Losses ” shall mean any and all damages, demands, payments, obligations, penalties, assessments, disbursements, claims, costs, liabilities, losses, causes of action, and expenses, including interest, awards, judgments, settlements, fines, fees, costs of defense and reasonable attorneys’ fees, costs of accountants, expert witnesses and other professional advisors and costs of investigation and preparation of any kind or nature whatsoever.

Section 3.2                    Indemnification by CWEI .   CWEI shall defend, indemnify and hold harmless LARIAT and its affiliates, and all of its and their directors, officers, employees,  contractors, agents, and representatives (the “ LARIAT Indemnitees ”) from and against any and all Losses