Document:

<PAGE>

                                                                     Exhibit 4.3

                          SECOND SUPPLEMENTAL INDENTURE

      SECOND SUPPLEMENTAL INDENTURE (this "SECOND SUPPLEMENTAL INDENTURE"),
dated as of March 31, 2004 among Grey Wolf Mexico Holdings LLC, a Nevada limited
liability company (the "NEW GUARANTOR"), a subsidiary of Grey Wolf, Inc., a
Texas Corporation (the "COMPANY"), the Company, the Guarantors under the
Indenture referred to below (the "EXISTING GUARANTORS"), and JPMorgan Chase
Bank, a New York banking corporation, as trustee under the Indenture referred to
below (the "TRUSTEE").

                              W I T N E S S E T H :

      WHEREAS, the Company has heretofore executed and delivered to the Trustee
an Indenture (as such may be amended from time to time, the "INDENTURE"), dated
as of May 7, 2003, providing for the issuance of an aggregate principal amount
of $150,000,00 of 3.75% Contingent Convertible Senior Notes due 2023 (the
"SECURITIES");

      WHEREAS, Section 11.08 of the Indenture provides that the Company is
required to cause the New Guarantor to execute and deliver to the Trustee a
supplemental indenture pursuant to which the New Guarantor shall jointly and
severally and unconditionally and irrevocably guarantee all of the Company's
Obligations under the Securities and the Indenture pursuant to a Guarantee
contained in the Indenture on the terms and conditions set forth herein; and

      WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee, the
Company and Existing Guarantors are authorized to execute and deliver this
Second Supplemental Indenture;

      NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the New
Guarantor, the Company, the Existing Guarantors and the Trustee mutually
covenant and agree for the equal and ratable benefit of the holders of the
Securities as follows:

      1.    Definitions. (a) Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

            (b)   For all purposes of this Second Supplemental Indenture, except
as otherwise herein expressly provided or unless the context otherwise requires:
(i) the terms and expressions used herein shall have the same meanings as
corresponding terms and expressions used in the Indenture; and (ii) the words
"HEREIN," "HEREOF" and "HEREBY" and other words of similar import used in this
Second Supplemental Indenture refer to this Second Supplemental Indenture as a
whole and not to any particular section hereof.

      2.    Agreement to Guarantee. The New Guarantor hereby agrees, jointly and
severally and unconditionally and irrevocably, with all other Guarantors, to
guarantee the Company's Obligations under the Securities and the Indenture on
the terms and subject to the conditions set forth in Article 11 of the Indenture
and to be bound by all other applicable provisions of the Indenture. From and
after the date hereof, the New Guarantor shall be a Guarantor for all purposes
under the Indenture and the Securities.

<PAGE>

      3.    Ratification of Indenture; Second Supplemental Indenture Part of
Indenture. Except as expressly amended hereby, the Indenture is in all respects
ratified and confirmed and all the terms, conditions and provisions thereof
shall remain in full force and effect. This Second Supplemental Indenture shall
form a part of the Indenture for all purposes, and every Holder of Securities
heretofore or hereafter authenticated and delivered shall be bound hereby.

      4.    Governing Law. THIS SECOND SUPPLEMENTAL INDENTURE SHALL BE GOVERNED
BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK BUT
WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT
THAT THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED
THEREBY.

      5.    Trustee Makes No Representation. The Trustee makes no representation
as to the validity or sufficiency of this Second Supplemental Indenture.

      6.    Counterparts. The parties may sign any number of copies of this
Second Supplemental Indenture. Each signed copy shall be an original, but all of
them together represent the same agreement.

      7.    Effect of Headings. The Section headings herein are for convenience
only and shall not effect the construction thereof.

      IN WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed as of the date first above written.

                                       NEW GUARANTOR:

                                       GREY WOLF MEXICO HOLDINGS LLC

                                       By: _____________________________________
                                           David W. Wehlmann, Manager

                                       COMPANY:

                                       GREY WOLF, INC.

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                        2

<PAGE>

                                       EXISTING GUARANTORS:

                                       GREY WOLF DRILLING COMPANY L.P.

                                           BY: GREY WOLF HOLDINGS COMPANY,
                                               ITS SOLE GENERAL PARTNER

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       GREY WOLF LLC

                                           BY: GREY WOLF HOLDINGS COMPANY,
                                               ITS SOLE MEMBER

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       GREY WOLF HOLDINGS COMPANY

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       MURCO DRILLING CORPORATION

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       GREY WOLF INTERNATIONAL, INC.

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                        3

<PAGE>

                                       DI/PERFENSA INC.

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       DI ENERGY, INC.

                                       By: _____________________________________
                                           David W. Wehlmann, Executive Vice
                                           President and Chief Financial Officer

                                       TRUSTEE:

                                       JPMORGAN CHASE BANK

                                       By: _____________________________________
                                       Name: ___________________________________
                                       Title: __________________________________

                                        4<PAGE>

                                                                    Exhibit 10.1

                        THIRD AMENDMENT TO LOAN AGREEMENT

      THIS THIRD AMENDMENT TO LOAN AGREEMENT (this "Amendment") is made and
entered into as of this 1st day of May, 2003, by and among THE CIT
GROUP/BUSINESS CREDIT, INC., a New York corporation (hereinafter "CITBC"), in
its individual capacity as a Lender and as Agent for the Lenders hereinafter
named (hereinafter the "AGENT"), Foothill Capital Corporation, a California
corporation ("FCC"), and any other party hereafter becoming a Lender pursuant to
Section 12.4(b) of the Loan Agreement (as hereinafter defined), each
individually sometimes referred to as a "LENDER" and, collectively, the
"LENDERS"), GREY WOLF DRILLING COMPANY L.P., a Texas limited partnership (the
"BORROWER"), GREY WOLF, INC., a Texas corporation (the "PARENT"), GREY WOLF
HOLDINGS COMPANY, a Nevada corporation ("HOLDINGS"), GREY WOLF LLC, a Louisiana
limited liability company ("GWLLC"), DI ENERGY, INC., a Texas corporation
("ENERGY"), GREY WOLF INTERNATIONAL, INC., a Texas corporation
("INTERNATIONAL"), DI/PERFENSA, INC., a Texas corporation ("PERFENSA"), MURCO
DRILLING CORP., a Delaware corporation ("MURCO") (Parent, Holdings, GWLLC,
Energy, International, Perfensa and Murco are referred to collectively herein as
the "GUARANTORS").

                                    RECITALS

      A.    WHEREAS, pursuant to the terms and subject to the conditions of that
certain Loan Agreement dated as of January 14, 1999 between the parties hereto,
as amended by that certain First Amendment to Loan Agreement dated December 20,
2001 (such Loan Agreement, as the same was previously amended, is hereby amended
and may hereafter be amended from time to time, being hereinafter referred to as
the "Loan Agreement"), the Borrower was granted a $50,000,000 revolving line of
credit which included a letter of credit facility;

      B.    WHEREAS, the indebtedness of the Borrower to the Lenders is
currently evidenced by that certain Revolving Note dated December 20, 2001 (the
"Revolving Note"), executed by the Borrower and payable to CITBC as Agent for
the benefit of the Lenders in the stated principal amount of $75,000,000;

      C.    WHEREAS, payment of the Obligations of the Borrower are supported by
the guarantees of the Guarantors contained in Section 13 of the Loan Agreement;

      D.    WHEREAS, to secure, in part, the indebtedness under the Loan
Agreement and the Revolving Note (and all renewals, extensions, modifications
and/or rearrangements thereof and in connection therewith) and all other
indebtedness, liabilities and obligations of the Borrower and the Guarantors to
the Agent for the benefit of the Lenders, then existing or thereafter arising,
(i) the Borrower and the Guarantors have heretofore executed in favor of the
Agent certain Credit Documents (as defined in the Loan Agreement), including,
without limitation, the Security Documents (as defined in the Loan Agreement),
which Credit Documents shall continue as amended in connection herewith in full
force and effect upon the execution of this Amendment, all of the Credit
Documents to continue to secure the payment by the Borrower

THIRD AMENDMENT TO LOAN AGREEMENT       Page 1

<PAGE>

and the Guarantors of the Obligations (as defined in the Loan Agreement) all as
more fully set forth therein and herein;

      E.    WHEREAS, the Borrower has requested and, pursuant to the terms and
subject to the conditions hereof and in connection herewith, the Agent and the
Lenders have agreed to modify the definition of Permitted Refinancing;

      F.    WHEREAS, in furtherance of the foregoing and to evidence the
agreements of the parties hereto in relation thereto the parties hereto desire
to amend the Loan Agreement as hereinafter provided;

      NOW, THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the Borrower, the Guarantors, the Agent and the Lenders,
intending to be legally bound, agree as follows:

                                    AGREEMENT

                                    ARTICLE I
                                   DEFINITIONS

      1.01  Capitalized terms used in this Amendment are defined in the Loan
Agreement, as amended hereby, unless otherwise stated.

                                   ARTICLE II
                          AMENDMENTS TO LOAN AGREEMENT

      Effective as of the respective date herein indicated, the Loan Agreement
is hereby amended as follows:

      2.01  AMENDMENT AND RESTATEMENT OF DEFINITION OF "PERMITTED REFINANCING".
Effective as of the date of execution of this Amendment, the definition of
"Permitted Refinancing" set forth in Section 10 of the Loan Agreement is amended
and restated to read in its entirety as follows:

      " `Permitted Refinancing' means a refinancing of all or any portion of the
      Indebtedness evidenced by (i) the Parent's Senior Notes due 2007 issued in
      1997, in the aggregate principal amount of $175,000,000, and (ii) the
      Parent's Senior Notes due 2007 issued in 1998 in the aggregate principal
      amount of $75,000,000 (either with the same payees or different financing
      sources), including a restructure or restatement of such existing
      Indebtedness or a new loan to repay such existing Indebtedness, so long as
      (a) the terms of the refinanced Indebtedness are not materially more
      favorable to the payee(s) and are not less favorable to the Lenders than
      the existing Indebtedness which was refinanced, (b) no Default or Event of
      Default will exist immediately after the completion of such

THIRD AMENDMENT TO LOAN AGREEMENT       Page 2

<PAGE>

      refinancing, and (c) such refinancing Indebtedness is subordinated in
      right of payment to the Obligations at least to the same extent as the
      Indebtedness being refinanced."

                                   ARTICLE III
                              CONDITIONS PRECEDENT

      3.01  CONDITIONS TO EFFECTIVENESS. The effectiveness of this Amendment is
subject to the satisfaction of the following conditions precedent in a manner
satisfactory to Agent, unless specifically waived in writing by Agent:

            (a)   Agent shall have received each of the following, each in form
      and substance satisfactory to Agent, in its sole discretion, and, where
      applicable, each duly executed by each party thereto, other than Agent:

                  (i)   This Amendment, duly executed by the Borrower and the
            Guarantors;

                  (ii)  certified copies of the resolutions of the Board of
            Directors of each of the Borrower and the Guarantors authorizing the
            execution, delivery and performance of this Amendment and any and
            all other Credit Documents executed by any of the Borrower or the
            Guarantors in connection therewith, along with a certificate of
            incumbency certified by the secretary of each of the Borrower and
            the Guarantors with specimen signatures of the officers of the
            Borrower and the Guarantors who are authorized to sign such
            documents, all in form and substance satisfactory to the Agent; and

                  (iii) All other documents Agent may request with respect to
            any matter relevant to this Amendment or the transactions
            contemplated hereby.

            (b)   The representations and warranties contained herein and in the
      Loan Agreement and the other Credit Documents (as defined in the Loan
      Agreement), as each is amended hereby, shall be true and correct as of the
      date hereof, as if made on the date hereof.

            (c)   No Default or Event of Default shall have occurred and be
      continuing, unless such Default or Event of Default has been otherwise
      specifically waived in writing by Agent.

            (d)   All corporate proceedings taken in connection with the
      transactions contemplated by this Amendment and all documents, instruments
      and other legal matters incident thereto shall be satisfactory to Agent.

THIRD AMENDMENT TO LOAN AGREEMENT       Page 3

<PAGE>

                                   ARTICLE IV
                  RATIFICATIONS, REPRESENTATIONS AND WARRANTIES

      4.01  RATIFICATIONS. The terms and provisions set forth in this Amendment
shall modify and supersede all inconsistent terms and provisions set forth in
the Loan Agreement and the other Credit Documents, and, except as expressly
modified and superseded by this Amendment, the terms and provisions of the Loan
Agreement and the other Credit Documents are ratified and confirmed and shall
continue in full force and effect. The Borrower, Agent and Lenders agree that
the Loan Agreement and the other Credit Documents, as amended hereby, shall
continue to be legal, valid, binding and enforceable in accordance with their
respective terms.

      4.02  REPRESENTATIONS AND WARRANTIES. The Borrower and Guarantor (the
"Credit Parties") hereby represent and warrant to Agent and the Lenders that (a)
the execution, delivery and performance of this Amendment and any and all other
Credit Documents executed and/or delivered in connection herewith have been
authorized by all requisite corporate action on the part of the Credit Parties
and will not violate the organizational documents of the Credit Parties; (b) the
Managers or Board of Directors of each of the Credit Parties (or the Board of
Directors of the corporate general partners of any Credit Party that is a
limited partnership) has authorized the execution, delivery and performance of
this Amendment and any and all other Credit Documents executed and/or delivered
in connection herewith; (c) the representations and warranties contained in the
Loan Agreement, as amended hereby, and any other Credit Document are true and
correct on and as of the date hereof and on and as of the date of execution
hereof as though made on and as of each such date; (d) no Default or Event of
Default under the Loan Agreement, as amended hereby, has occurred and is
continuing, unless such Default or Event of Default has been specifically waived
in writing by Agent; (e) the Credit Parties are in full compliance with all
covenants and agreements contained in the Loan Agreement and the other Credit
Documents, as amended hereby; and (f) the Credit Parties have not amended their
(i) Articles (or Certificates) of Incorporation or their Bylaws, if a
corporation, (ii) limited partnership agreement or certificate of limited
partnership, if a limited partnership, since the date of the Loan Agreement, or
(iii) Articles of Organization or operating agreement, if a limited liability
company, except as otherwise disclosed to Agent.

                                    ARTICLE V
                            MISCELLANEOUS PROVISIONS

      5.01  SURVIVAL OF REPRESENTATIONS AND WARRANTIES. All representations and
warranties made in the Loan Agreement or any other Credit Document, including,
without limitation, any document furnished in connection with this Amendment,
shall survive the execution and delivery of this Amendment and the other Credit
Documents, and no investigation by Agent or any closing shall affect the
representations and warranties or the right of Agent to rely upon them.

      5.02  REFERENCE TO LOAN AGREEMENT. Each of the Loan Agreement and the
other Credit Documents, and any and all other Credit Documents, documents or
instruments now or

THIRD AMENDMENT TO LOAN AGREEMENT       Page 4

<PAGE>

hereafter executed and delivered pursuant to the terms hereof or pursuant to the
terms of the Loan Agreement, as amended hereby, are hereby amended so that any
reference in the Loan Agreement and such other Credit Documents to the Loan
Agreement shall mean a reference to the Loan Agreement, as amended hereby.

      5.03  EXPENSES OF AGENT. As provided in the Loan Agreement, the Borrower
agrees to pay on demand all reasonable costs and expenses incurred by Agent in
connection with the preparation, negotiation, and execution of this Amendment
and the other Credit Documents executed pursuant hereto and any and all
amendments, modifications, and supplements thereto, including, without
limitation, the reasonable costs and fees of Agent's legal counsel, and all
reasonable costs and expenses incurred by Agent in connection with the
enforcement or preservation of any rights under the Loan Agreement, as amended
hereby, or any other Credit Documents, including, without limitation, the
reasonable costs and fees of Agent's legal counsel.

      5.04  SEVERABILITY. Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

      5.05  SUCCESSORS AND ASSIGNS. This Amendment is binding upon and shall
inure to the benefit of Agent, the Lenders, and the Credit Parties and their
respective successors and assigns, except that the Credit Parties may not assign
or transfer any of their rights or obligations hereunder without the prior
written consent of Agent.

      5.06  COUNTERPARTS. This Amendment may be executed in one or more
counterparts, each of which when so executed shall be deemed to be an original,
but all of which when taken together shall constitute one and the same
instrument.

      5.07  EFFECT OF WAIVER. No consent or waiver, express or implied, by Agent
to or for any breach of or deviation from any covenant or condition by the
Credit Parties shall be deemed a consent to or waiver of any other breach of the
same or any other covenant, condition or duty.

      5.08  HEADINGS. The headings, captions, and arrangements used in this
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.

      5.09  APPLICABLE LAW. THIS AMENDMENT AND ALL OTHER CREDIT DOCUMENTS
EXECUTED PURSUANT HERETO SHALL BE DEEMED TO HAVE BEEN MADE AND TO BE PERFORMABLE
IN AND SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF NEW YORK.

      5.10  FINAL AGREEMENT. THE AGREEMENT AND THE OTHER CREDIT DOCUMENTS, EACH
AS AMENDED HEREBY, REPRESENT THE ENTIRE EXPRESSION OF THE PARTIES WITH RESPECT
TO THE SUBJECT MATTER HEREOF ON THE DATE THIS AMENDMENT IS EXECUTED. THE LOAN
AGREEMENT AND THE OTHER CREDIT DOCUMENTS, AS AMENDED HEREBY, MAY NOT BE
CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS

THIRD AMENDMENT TO LOAN AGREEMENT       Page 5

<PAGE>

OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES. NO
MODIFICATION, RESCISSION, WAIVER, RELEASE OR AMENDMENT OF ANY PROVISION OF THIS
AMENDMENT SHALL BE MADE, EXCEPT BY A WRITTEN AGREEMENT SIGNED BY THE CREDIT
PARTIES AND THE AGENT.

      5.11  FINANCING STATEMENTS. Agent is hereby authorized by each Credit
Parties to file (including pursuant to the applicable terms of the UCC) from
time to time any financing statements, continuations or amendments covering the
Collateral whether or not the signature of any such Credit Party appears
thereon.

      5.12  RELEASE BY BORROWER. THE BORROWER HEREBY ACKNOWLEDGES THAT BORROWER
HAS NO DEFENSE, COUNTERCLAIM, OFFSET, CROSS-COMPLAINT, CLAIM OR DEMAND OF ANY
KIND OR NATURE WHATSOEVER THAT CAN BE ASSERTED TO REDUCE OR ELIMINATE ALL OR ANY
PART OF ITS LIABILITY TO REPAY THE "OBLIGATIONS" OR TO SEEK AFFIRMATIVE RELIEF
OR DAMAGES OF ANY KIND OR NATURE FROM AGENT OR THE LENDERS. THE BORROWER HEREBY
VOLUNTARILY AND KNOWINGLY RELEASE AND FOREVER DISCHARGE AGENT AND THE LENDERS,
AND THEIR RESPECTIVE PREDECESSORS, AGENTS, EMPLOYEES, SUCCESSORS AND ASSIGNS
(THE "RELEASED PARTIES"), FROM ALL POSSIBLE CLAIMS, DEMANDS, ACTIONS, CAUSES OF
ACTION, DAMAGES, COSTS, EXPENSES, AND LIABILITIES WHATSOEVER, KNOWN OR UNKNOWN,
ANTICIPATED OR UNANTICIPATED, SUSPECTED OR UNSUSPECTED, FIXED, CONTINGENT, OR
CONDITIONAL, AT LAW OR IN EQUITY, ORIGINATING IN WHOLE OR IN PART ON OR BEFORE
THE DATE THIS AMENDMENT IS EXECUTED, WHICH THE BORROWER MAY NOW OR HEREAFTER
HAVE AGAINST THE RELEASED PARTIES, IF ANY, AND IRRESPECTIVE OF WHETHER ANY SUCH
CLAIMS ARISE OUT OF CONTRACT, TORT, VIOLATION OF LAW OR REGULATIONS, OR
OTHERWISE, AND ARISING FROM ANY "LOANS", INCLUDING, WITHOUT LIMITATION, ANY
CONTRACTING FOR, CHARGING, TAKING, RESERVING, COLLECTING OR RECEIVING INTEREST
IN EXCESS OF THE HIGHEST LAWFUL RATE APPLICABLE, THE EXERCISE OF ANY RIGHTS AND
REMEDIES UNDER THE LOAN AGREEMENT OR OTHER CREDIT DOCUMENTS, AND NEGOTIATION FOR
AND EXECUTION OF THIS AMENDMENT.

      5.13  RELEASE BY GUARANTORS. Each Guarantor hereby consents to the terms
of this Amendment, confirms and ratifies the terms of the guarantee by such
Guarantor for the benefit of Agent and the other Lenders set forth in Section 13
of the Loan Agreement (each a "Guarantee" and collectively the "Guarantees"),
and acknowledges that such Guarantor's Guarantee is in full force and effect and
ratifies the same and that such Guarantor each has no defense, counterclaim,
set-off or any other claim to diminish such Guarantor's liability under its
Guarantee. EACH GUARANTOR HEREBY VOLUNTARILY AND KNOWINGLY RELEASES AND FOREVER
DISCHARGES THE RELEASED PARTIES, FROM ALL POSSIBLE CLAIMS, DEMANDS, ACTIONS,
CAUSES OF ACTION, DAMAGES, COSTS, EXPENSES, AND LIABILITIES WHATSOEVER, KNOWN OR
UNKNOWN, ANTICIPATED OR UNANTICIPATED, SUSPECTED OR UNSUSPECTED, FIXED,
CONTINGENT, OR CONDITIONAL, AT LAW OR IN EQUITY, ORIGINATING IN

THIRD AMENDMENT TO LOAN AGREEMENT       Page 6

<PAGE>

WHOLE OR IN PART ON OR BEFORE THE DATE THIS AMENDMENT IS EXECUTED, WHICH THE
GUARANTORS MAY NOW OR HEREAFTER HAVE AGAINST THE RELEASED PARTIES, IF ANY, AND
IRRESPECTIVE OF WHETHER ANY SUCH CLAIMS ARISE OUT OF CONTRACT, TORT, VIOLATION
OF LAW OR REGULATIONS, OR OTHERWISE, AND ARISING FROM ANY "LOANS", INCLUDING,
WITHOUT LIMITATION, ANY CONTRACTING FOR, CHARGING, TAKING, RESERVING, COLLECTING
OR RECEIVING INTEREST IN EXCESS OF THE HIGHEST LAWFUL RATE APPLICABLE, THE
EXERCISE OF ANY RIGHTS AND REMEDIES UNDER THE LOAN AGREEMENT OR OTHER CREDIT
DOCUMENTS, AND NEGOTIATION FOR AND EXECUTION OF THIS AMENDMENT.

         IN WITNESS WHEREOF, this Amendment has been executed and is effective
as of the date first above-written.

                                       BORROWER:

                                       GREY WOLF DRILLING COMPANY L.P.

                                       By: Grey Wolf Holdings Company,
                                           its general partner

                                           By: _________________________________
                                               David W. Wehlmann
                                               Executive Vice President and
                                               Chief Financial Officer

                                       GUARANTORS:

                                       GREY WOLF, INC.

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

THIRD AMENDMENT TO LOAN AGREEMENT           Page 7

<PAGE>

                                       GREY WOLF HOLDINGS COMPANY

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

                                       GREY WOLF LLC,

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

                                       DI ENERGY, INC.

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

                                       GREY WOLF INTERNATIONAL, INC.

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

                                       DI/PERFENSA, INC.

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

THIRD AMENDMENT TO LOAN AGREEMENT           Page 8

<PAGE>

                                       MURCO DRILLING CORP.

                                       By: _____________________________________
                                           David W. Wehlmann
                                           Executive Vice President and
                                           Chief Financial Officer

                                       LENDERS:

                                       THE CIT GROUP/BUSINESS CREDIT, INC.
                                       as Agent and Lender

                                       By: _____________________________________
                                       Name: ___________________________________
                                       Title: __________________________________

                                       Revolving Loan Commitment:  $40,000,000

                                       FOOTHILL CAPITAL CORPORATION,
                                       as Lender

                                       By: _____________________________________
                                       Name: ___________________________________
                                       Title: __________________________________

                                       Revolving Loan Commitment:  $35,000,000

THIRD AMENDMENT TO LOAN AGREEMENT           Page 9

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