Exhibit 4.1

Execution Version

SIXTH SUPPLEMENTAL INDENTURE

among

CARRIZO OIL & GAS, INC.,

CCBM, INC.,

CHAMA PIPELINE HOLDING LLC

and

WELLS FARGO BANK, NATIONAL ASSOCIATION,

as Trustee

May 4, 2011

TABLE OF CONTENTS

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CARRIZO OIL & GAS, INC.

SIXTH SUPPLEMENTAL INDENTURE

SIXTH SUPPLEMENTAL INDENTURE, dated as of May 4, 2011 (the “Sixth Supplemental Indenture”), among CCBM, Inc., a Delaware limited liability company (“CCBM”), Chama Pipeline Holding LLC, a Delaware limited liability company (“Chama”), Carrizo Oil and Gas, Inc., a Texas corporation (the “Company”), and Wells Fargo Bank, National Association (the “Trustee”).

W I T N E S S E T H :

WHEREAS, the Company, certain of its Subsidiaries (including CCBM and Chama) and the Trustee heretofore executed and delivered an Indenture, dated as of May 28, 2008 (the “Original Indenture”), providing for the issuance from time to time of one or more series of the Company’s Securities;

WHEREAS, the Company issued $400,000,000 aggregate principal amount of 8.625% Senior Notes due 2018 pursuant to the Original Indenture, as supplemented by the Fourth Supplemental Indenture (the “Fourth Supplemental Indenture”) thereto between the Company and the Trustee dated November 2, 2010 (the Original Indenture, as supplemented by the First Supplemental Indenture thereto dated as of May 28, 2008, the Second Supplemental Indenture thereto dated as of May 14, 2009, the Third Supplemental Indenture thereto dated as of October 19, 2009 and the Fourth Supplemental Indenture, the “Indenture”);

WHEREAS, CCBM and Chama are parties to and Subsidiary Guarantors under the Indenture;

WHEREAS, Section 10.04 of the Indenture permits the release of any Subsidiary Guarantor as a party to the Indenture at such time as such Subsidiary Guarantor ceases both (i) to guarantee any other Indebtedness of the Company and any Indebtedness of any other Restricted Subsidiary (except as a result of payment under any such other guarantee) and (ii) to be an obligor with respect to any Indebtedness under any Credit Facility; and

WHEREAS, CCBM and Chama (i) no longer guarantee any other Indebtedness of the Company or any Indebtedness of any other Restricted Subsidiary and (ii) are no longer obligors with respect to any Indebtedness under any Credit Facility, CCBM, Chama and the Company propose, pursuant to Section 10.04 of the Indenture, to amend and supplement the Indenture to release CCBM and Chama as Subsidiary Guarantors thereunder;

NOW, THEREFORE:

In consideration of the premises provided for herein, CCBM, Chama, the Company and the Trustee mutually covenant and agree for the equal and proportionate benefit of all Holders of the Securities as follows:

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ARTICLE ONE

RELEASE OF SUBSIDIARY GUARANTORS

SECTION 101        Release of Subsidiary Guarantors.

Effective as of May 4, 2011, the parties agree that CCBM and Chama shall be released as parties to and as Subsidiary Guarantors under the Indenture and that CCBM and Chama shall have no further obligations or liabilities under the Indenture.

ARTICLE TWO

MISCELLANEOUS PROVISIONS

SECTION 201        Integral Part.

This Sixth Supplemental Indenture constitutes an integral part of the Indenture.

SECTION 202        General Definitions.

For all purposes of this Sixth Supplemental Indenture:

(a) capitalized terms used herein without definition shall have the meanings specified in the Indenture; and

(b) the terms “herein,” “hereof,” “hereunder” and other words of similar import refer to this Sixth Supplemental Indenture.

SECTION 203        Adoption, Ratification and Confirmation.

The Indenture, as supplemented and amended by this Sixth Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed.

SECTION 204        Counterparts.

This Sixth Supplemental Indenture may be executed in any number of counterparts, each of which when so executed shall be deemed an original; and all such counterparts shall together constitute but one and the same instrument.

SECTION 205        Governing Law.

THIS SIXTH SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

SECTION 206        The Trustee.

The Trustee shall not be responsible in any manner whatsoever for or in respect of

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the validity or sufficiency of this Sixth Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by CCBM, Chama and the Company.

[Remainder of Page Intentionally Left Blank]

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IN WITNESS WHEREOF, the parties hereto have caused this Sixth Supplemental Indenture to be duly executed as of the day and year first written above.

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