Exhibit 10.6

TRANSITION AGREEMENT

This Transition Agreement dated as of June 10, 2013 (“Transition Agreement”) is
made by and between Contango Oil & Gas Company (the “Company”) and Marc Duncan
(the “Employee”).

RECITALS

WHEREAS, the Employee is currently employed as the Company’s Senior Vice
President — Engineering;

WHEREAS, the Employee is employed through a co-employment arrangement with
Insperity Holdings, Inc. (“Insperity”);

WHEREAS, the Company, Contango Acquisition, Inc. and Crimson Exploration Inc.
(“Crimson”), have entered into an agreement and Plan of Merger dated as of
April 29, 2013, pursuant to which a wholly owned subsidiary of the Company will
merge with and into Crimson, with Crimson surviving as a wholly owned subsidiary
of the Company (the “Merger”);

WHEREAS, the Company and the Employee have mutually agreed that Employee’s
employment with the Company and Insperity will terminate effective as of the
closing date of the Merger (the “Closing Date”);

NOW THEREFORE, in consideration of the mutual promises made herein, Employee and
the Company hereby agree as follows:

1. The Employee will continue to provide full-time services in his current
position as requested by the Company’s Chief Executive Officer through the
Closing Date. The Employee’s employment with the Company and Insperity will
terminate effective as of the Closing Date.

2. If the Employee continues in employment through the Closing Date and timely
executes and does not revoke the Separation and General Release Agreement
attached as Exhibit A, the Company will provide Employee with the following:

(a) Severance Payment. A cash severance payment in the amount of $250,000, which
is equal to one year of the Employee’s base salary. The severance payment will
be paid in a lump sum cash payment on the first payroll date in January of the
year following the year of the Employee’s termination date.

(b) Deferred Bonus. Any unpaid deferred bonus at the Employee’s termination date
(which will be $75,000 if the Closing Date occurs between June 30, 2013 and
June 30, 2014). The deferred bonus will be paid in a lump sum cash payment on
the first payroll date in January of the year following the year of the
Employee’s termination date.

3. All payments shall be subject to applicable income and employment withholding
taxes in accordance with the Company’s normal payroll practices.

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4. Without regard to whether the Employee signs the Separation and General
Release Agreement, upon his termination of employment, the Employee shall
receive any earned but unpaid salary through the termination date, any accrued
but unpaid vacation through the termination date, and any accrued vested
benefits in accordance with the applicable plan documents.

5. This Transition Agreement does not affect the right of the Company to
terminate the Employee’s employment, with or without Cause. Notwithstanding
anything in this Transition Agreement to the contrary, in the event of
termination for Cause, no payments shall be made under this Transition
Agreement, and this Transition Agreement shall terminate. For purposes of this
Transition Agreement, “Cause” means (i) commission of an act of dishonesty,
fraud, embezzlement or theft in the course of his employment with the Company;
(iii) engaging in conduct which causes, or is likely to cause, material damage
to the property or reputation of the Company; (iv) failure to perform
satisfactorily the material duties of the Employee’s position after receipt of a
written or verbal warning from the Company (other than by reason of death or
disability); (v) commission of a felony or a crime of moral turpitude;
(vi) failure to adhere to the Company’s policies; or (vii) disclosure of
confidential information of the Company to persons not entitled to receive such
information.

6. This Transition Agreement contains the entire understanding of the parties
with respect to the matters covered herein. This Agreement supersedes and
replaces all prior statements, representations, negotiations, promises or
agreements (written and oral) relating to the subject matters covered herein,
including, without limitation, the offer letter entered into by the parties
dated May 17, 2005, but excluding any proprietary information, inventions
assignment and confidentiality agreements between the Employee and the Company.

7. Section 409A. The payments under this Transition Agreement are intended to
comply with the requirements of Section 409A of the Internal Revenue Code, or to
be exempt from such requirements pursuant to the “short term deferral exception”
or the “separation pay exception” to Section 409A. If this Transition Agreement
is subject to the requirements of Section 409A, in no event will the timing of
the execution of the Agreement, directly or indirectly, result in the Employee
designating the calendar year of payment.

8. This Transition Agreement shall be governed by the laws of the state of
Texas.

WITNESS the following signatures:

 

CONTANGO OIL AND GAS COMPANY          Dated:     June 10, 2013                  
Signature:     /s/ Joseph J. Romano         Title:     President and Chief
Executive Officer           MARC DUNCAN             Dated:      June 10,
2013                   Signature:     /s/ Marc Duncan              

 

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Exhibit A

Separation and General Release Agreement

 

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