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Exhibit 10.1

FIRST AMENDMENT TO CREDIT AGREEMENT

        THIS FIRST AMENDMENT TO CREDIT AGREEMENT (herein called this
"Amendment"), dated as of April 21, 2003, is among Cimarex Energy Co., a
Delaware corporation ("Borrower"), Bank One, NA, a national banking association
having its principal office in Chicago, Illinois, as LC Issuer and as
Administrative Agent, and the Lenders party to the Original Agreement defined
below ("Lenders").

W I T N E S S E T H:

        WHEREAS, Borrower, Administrative Agent and Lenders entered into that
certain Credit Agreement dated as of October 2, 2002 (as amended, supplemented,
or restated to the date hereof, the "Original Agreement"), for the purpose and
consideration therein expressed, whereby Lenders became obligated to make loans
to Borrower as therein provided; and

        WHEREAS, Borrower, Administrative Agent and Lenders desire to amend the
Original Agreement as set forth herein;

        NOW, THEREFORE, in consideration of the premises and the mutual
covenants and agreements contained herein and in the Original Agreement, in
consideration of the loans which may hereafter be made by Lenders to Borrower,
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged, the parties hereto do hereby agree as follows:

ARTICLE I
DEFINITIONS AND REFERENCES

        § 1.1.    Terms Defined in the Original Agreement.    Unless the context
otherwise requires or unless otherwise expressly defined herein, the terms
defined in the Original Agreement shall have the same meanings whenever used in
this Amendment.

        § 1.2.    Other Defined Terms.    Unless the context otherwise requires,
the following terms when used in this Amendment shall have the meanings assigned
to them in this Section 1.2.

        "Amendment" means this First Amendment to Credit Agreement.

        "Amendment Documents" means this Amendment and any other documents and
agreements executed and delivered pursuant hereto.

        "Credit Agreement" means the Original Agreement as amended hereby.

ARTICLE II
AMENDMENTS TO ORIGINAL AGREEMENT

        § 2.1.    Defined Terms.    Section 1.1 of the Original Agreement is
hereby amended to add the following definitions thereto in appropriate
alphabetical order to read as follows:

        "Dividend' means, as to any Person, any declaration or payment of any
dividend or the making of any distribution, loan, advance or investment on or
with respect to any shares of a Person's capital stock (other than dividends or
distributions payable solely in shares or other evidence of ownership of such
Person's capital stock)."

        "Restricted Payment' means (a) any Dividend and (b) any payment on
account of the purchase, redemption or other acquisition or retirement by a
Person of any of such Person's capital stock (except capital stock acquired on
the conversion or exchange thereof into or for other capital stock of such
Person)."

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        § 2.2.    Production Reports.    Section 6.1(vii) of the Original
Agreement is hereby amended in its entirety to read as follows:

        "(xii) By March 31 and September 30 of each year, beginning March 31,
2003, a report describing the gross volume of production and sales attributable
to production during the preceding six-month period from the properties
described in the Engineering Report in Section 6.1(x) or Section 6.1(xi) and
describing the related severance taxes, other taxes, and leasehold operating
expenses attributable thereto and incurred during such month."

        § 2.3.    Restricted Payments.    Section 7.1 of the Original Agreement
is hereby amended in its entirety to read as follows:

        "7.1.    Restricted Payments.    The Borrower will not, nor will it
permit any Subsidiary to, directly or indirectly, declare or make any Restricted
Payment; provided that (a) any Subsidiary may declare and pay Dividends to the
Borrower or to a Wholly-Owned Subsidiary and (b) for so long as no Default,
Unmatured Default or Deficiency (as defined in Section 2.8) exists or would
exist after giving effect thereto, the Borrower and its Subsidiaries may declare
or make Restricted Payments which do not in the aggregate exceed an amount equal
to $25,000,000 during any fiscal year of the Borrower; provided that the
aggregate amount of Restricted Payments made pursuant to clause (b) of this
Section 7.1 shall never exceed $50,000,000."

        § 2.4.    Indebtedness.    Section 7.2 of the Original Agreement is
hereby amended to re-designate existing clause "(vi)" as clause "(vii)" and to
add a new clause (vi) thereto immediately following clause (v) thereof to read
as follows:

        "(vi) Indebtedness of Borrower in respect of guarantee obligations of
Cimarex Energy Services, Inc., an Oklahoma corporation, which do not in the
aggregate exceed $25,000,000 at any one time outstanding."

        § 2.5    Redetermination of the Borrowing Base.    Administrative Agent
hereby notifies Borrower that from the date hereof until the next date hereafter
as of which the Borrowing Base is redetermined, the Borrowing Base shall be
$275,000,000.

        § 2.6    Aggregate Commitment.    Borrower, Administrative Agent and
Lenders hereby confirm that as of the date hereof, the Aggregate Commitment is
$200,000,000.

ARTICLE III
CONDITIONS OF EFFECTIVENESS

        § 3.1.    Effective Date.    This Amendment shall become effective as of
the date first above written when and only when:

        (a)   Administrative Agent shall have received all of the following, at
Administrative Agent's office, duly executed and delivered and in form and
substance satisfactory to Administrative Agent, all of the following:

        (i)    this Amendment;

        (ii)   a certificate of the Secretary of Borrower dated the date of this
Amendment certifying: (i) that resolutions adopted by the Board of Directors of
the Borrower authorize the execution, delivery and performance of this Amendment
and the other Amendment Documents by Borrower; (ii) the names and true
signatures of the officers of the Borrower authorized to sign this Amendment and
the other Amendment Documents; and (iii) that all of the representations and
warranties set forth in Article IV hereof are true and correct at and as of the
time of such effectiveness; and

        (iii)  such other supporting documents as Administrative Agent may
reasonably request.

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        (b)   Borrower shall have paid, in connection with such Loan Documents,
all fees and reimbursements to be paid to Administrative Agent pursuant to any
Loan Documents, or otherwise due Administrative Agent and including fees and
disbursements of Administrative Agent's attorneys.

ARTICLE IV
REPRESENTATIONS AND WARRANTIES

        § 4.1.    Representations and Warranties of Borrower.    In order to
induce Administrative Agent and each Lender to enter into this Amendment,
Borrower represents and warrants to Administrative Agent and each Lender that:

        (a)   The representations and warranties contained in Article V of the
Original Agreement are true and correct at and as of the time of the
effectiveness hereof, except to the extent that the facts on which such
representations and warranties are based have been changed by the extension of
credit under the Credit Agreement.

        (b)   Borrower is duly authorized to execute and deliver this Amendment
and the other Amendment Documents and is and will continue to be duly authorized
to borrow monies and to perform its obligations under the Credit Agreement.
Borrower has duly taken all corporate action necessary to authorize the
execution and delivery of this Amendment and the other Amendment Documents and
to authorize the performance of the obligations of Borrower hereunder and
thereunder.

        (c)   The execution and delivery by Borrower of this Amendment and the
other Amendment Documents, the performance by Borrower of its obligations
hereunder and thereunder and the consummation of the transactions contemplated
hereby and thereby do not and will not conflict with any provision of law,
statute, rule or regulation or of the certificate of incorporation and bylaws of
Borrower, or of any material agreement, judgment, license, order or permit
applicable to or binding upon Borrower, or result in the creation of any lien,
charge or encumbrance upon any assets or properties of Borrower. Except for
those which have been obtained, no consent, approval, authorization or order of
any court or governmental authority or third party is required in connection
with the execution and delivery by Borrower of this Amendment and the other
Amendment Documents or to consummate the transactions contemplated hereby and
thereby.

        (d)   When duly executed and delivered, each of this Amendment and the
Credit Agreement will be a legal and binding obligation of Borrower, enforceable
in accordance with its terms, except as limited by bankruptcy, insolvency or
similar laws of general application relating to the enforcement of creditors'
rights and by equitable principles of general application.

        (e)   The audited annual consolidated financial statements of Borrower
dated as of December 31, 2002 fairly present the consolidated financial position
at such dates and the consolidated statement of operations and the changes in
consolidated financial position for the periods ending on such dates for
Borrower. Copies of such financial statements have heretofore been delivered to
each Lender. Since such dates no material adverse change has occurred in the
financial condition or businesses or in the consolidated financial condition or
businesses of Borrower.

ARTICLE V
MISCELLANEOUS

        § 5.1.    Ratification of Agreements.    The Original Agreement as
hereby amended is hereby ratified and confirmed in all respects. Any reference
to the Credit Agreement in any Loan Document shall be deemed to be a reference
to the Original Agreement as hereby amended. The execution, delivery and
effectiveness of this Amendment and the other Amendment Documents shall not,
except as expressly provided herein, operate as a waiver of any right, power or
remedy of Lenders under the Credit

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Agreement, the Notes, or any other Loan Document nor constitute a waiver of any
provision of the Credit Agreement, the Notes or any other Loan Document.

        § 5.2.    Survival of Agreements.    All representations, warranties,
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loans, and shall further survive until
all of the Obligations are paid in full. All statements and agreements contained
in any certificate or instrument delivered by Borrower or any Subsidiary
hereunder or under the Credit Agreement to any Lender shall be deemed to
constitute representations and warranties by, and/or agreements and covenants
of, Borrower under this Amendment and under the Credit Agreement.

        § 5.3.    Loan Documents.    This Amendment and the other Amendment
Documents are each a Loan Document, and all provisions in the Credit Agreement
pertaining to Loan Documents apply hereto and thereto.

        § 5.4.    CHOICE OF LAW.    THIS AMENDMENT SHALL BE CONSTRUED IN
ACCORDANCE THE INTERNAL LAWS OF THE STATE OF COLORADO, BUT GIVING EFFECT TO
FEDERAL LAWS APPLICABLE TO NATIONAL BANKS.

        § 5.5.    Counterparts.    This Amendment may be executed in any number
counterparts, all of which taken together shall constitute one agreement, and
any of the parties hereto may execute this Amendment by signing any such
counterpart. This Agreement shall be effective when it has been executed by the
Borrower, the Administrative Agent, the LC Issuer and the Lenders and each party
has notified the Administrative Agent by facsimile transmission or telephone
that it has taken such action.

        THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS OF THE PARTIES.

        IN WITNESS WHEREOF, this Amendment is executed as of the date first
above written.

 
 
CIMAREX ENERGY CO.
 
 
By:
 

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Paul Korus
Chief Financial Officer
 
 
BANK ONE, NA,
Individually, as LC Issuer and as Administrative Agent
 
 
By:
 

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J. Scott Fowler
Director, Capital Markets          

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BANK OF AMERICA, N.A., a Lender
 
 
By:
 

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Name:
Title:
 
 
BANK OF OKLAHOMA, N.A., a Lender
 
 
By:
 

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Name:
Title:
 
 
COMERICA BANK—TEXAS, a Lender
 
 
By:
 

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Name:
Title:
 
 
NATEXIS BANQUES POPULAIRES, a Lender
 
 
By:
 

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Name:
Title:
 
 
ROYAL BANK OF CANADA, a Lender
 
 
By:
 

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Name:
Title:
 
 
UNION BANK OF CALIFORNIA, N.A., a Lender
 
 
By:
 

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Name:
Title:
 
 
U.S. BANK NATIONAL ASSOCIATION, a Lender
 
 
By:
 

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Name:
Title:          

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WACHOVIA BANK, NATIONAL ASSOCIATION, a Lender
 
 
By:
 

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Name:
Title:
 
 
WELLS FARGO BANK, N.A., a Lender
 
 
By:
 

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Name:
Title:

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        First Amendment

CONSENT AND AGREEMENT

        Each undersigned Guarantor hereby (i) consents to the provisions of this
Amendment and the transactions contemplated herein, (ii) ratifies and confirms
the Subsidiary Guaranty dated as of October 2, 2002 made by it for the benefit
of Administrative Agent and Lenders executed pursuant to the Credit Agreement
and the other Loan Documents to which such Guarantor is a party, (iii) agrees
that all of its respective obligations and covenants thereunder shall remain
unimpaired by the execution and delivery of this Amendment and the other
documents and instruments executed in connection herewith, and (iv) agrees that
the Guaranty and such other Loan Documents shall remain in full force and
effect.

 
 
KEY PRODUCTION COMPANY, INC.
 
 
By:
 

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Paul Korus
Vice President, Chief Financial Officer & Treasurer
 
 
BROCK GAS SYSTEMS AND EQUIPMENT, INC.
 
 
By:
 

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Paul Korus
Vice President, Chief Financial Officer & Treasurer
 
 
COLUMBUS ENERGY CORP.
 
 
By:
 

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Paul Korus
Vice President, Chief Financial Officer & Treasurer
 
 
CIMAREX ENERGY SERVICES, INC.
 
 
By:
 

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Paul Korus
Vice President, Chief Financial Officer & Treasurer

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