THIRTY-SEVENTH SUPPLEMENTAL INDENTURE

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EXHIBIT 4.7.1(ll)

Upon recording, return to:
Ms. Shawne M. Keenan
Sutherland Asbill & Brennan LLP
999 Peachtree Street, N.E.
Atlanta, Georgia 30309-3996

PURSUANT TO § 44-14-35.1 OF OFFICIAL CODE OF GEORGIA ANNOTATED, THIS INSTRUMENT EMBRACES,
COVERS AND CONVEYS SECURITY TITLE TO AFTER-ACQUIRED PROPERTY OF THE GRANTOR

OGLETHORPE POWER CORPORATION
(AN ELECTRIC MEMBERSHIP CORPORATION),
GRANTOR,

to

U.S. BANK NATIONAL ASSOCIATION,
TRUSTEE

THIRTY-SEVENTH SUPPLEMENTAL
INDENTURE

Relating to the
Series 2006C-1 (Burke) Note
Series 2006C-2 (Burke) Note
Series 2006B (Monroe) Note

Dated as of October 1, 2006

FIRST MORTGAGE OBLIGATIONS

         THIS THIRTY-SEVENTH SUPPLEMENTAL INDENTURE , dated as of October 1, 2006, is between OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION) , formerly known as Oglethorpe Power Corporation (An Electric Membership Generation & Transmission Corporation), an electric membership corporation organized and existing under the laws of the State of Georgia, as Grantor (hereinafter called the "Company"), and U.S. BANK NATIONAL ASSOCIATION , a national banking association, as successor to SunTrust Bank, formerly known as SunTrust Bank, Atlanta, as Trustee (in such capacity, the "Trustee").

         WHEREAS, the Company has heretofore executed and delivered to the Trustee an Indenture, dated as of March 1, 1997 (hereinafter called the "Original Indenture") for the purpose of securing its Existing Obligations and providing for the authentication and delivery of Additional Obligations by the Trustee from time to time under the Original Indenture (capitalized terms used herein and not otherwise defined shall have the meanings assigned to them in the Original Indenture);

         WHEREAS, the Company has heretofore executed and delivered to the Trustee thirty-six Supplemental Indentures (the Original Indenture, as heretofore, hereby and hereafter supplemented and modified, being herein sometimes called the "Indenture"), and the Original Indenture and the thirty-six Supplemental Indentures have been recorded as set forth on Schedule 1 ;

Series 2006C-1 Burke Bonds

         WHEREAS, the Burke Authority has agreed to issue $50,000,000 in aggregate principal amount of Development Authority of Burke County Pollution Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 2006C-1 (the "Series 2006C-1 Burke Bonds"), and to loan the proceeds from the sale thereof to the Company pursuant to that certain Loan Agreement, dated as of October 1, 2006, relating thereto (the "Series 2006C-1 Burke Loan Agreement");

         WHEREAS, the Company's obligation to repay the loan of the proceeds of the Series 2006C-1 Burke Bonds is evidenced by that certain Series 2006C-1 (Burke) Note, dated the date of its authentication (the "Series 2006C-1 (Burke) Note"), from the Company to U.S. Bank National Association, as trustee (in such capacity, the "Series 2006C-1 Burke Trustee"), as assignee and pledgee of the Burke Authority pursuant to the Trust Indenture, dated as of October 1, 2006 (the "Series 2006C-1 Burke Indenture"), between the Burke Authority and the Series 2006C-1 Burke Trustee;

Series 2006C-2 Burke Bonds

         WHEREAS, the Burke Authority has agreed to issue $40,105,000 in aggregate principal amount of Development Authority of Burke County Pollution Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 2006C-2 (the "Series 2006C-2 Burke Bonds"; and together with the Series 2006C-1 Burke Bonds, the "Burke Bonds"), and to loan the proceeds from the sale thereof to the Company pursuant to that certain Loan Agreement, dated as of October 1, 2006, relating thereto (the "Series 2006C-2 Burke Loan Agreement");

         WHEREAS, the Company's obligation to repay the loan of the proceeds of the Series 2006C-2 Burke Bonds is evidenced by that certain Series 2006C-2 (Burke) Note, dated the date of its authentication (the "Series 2006C-2 (Burke) Note"), from the Company to U.S. Bank National Association, as trustee (in such capacity, the "Series 2006C-2 Burke Trustee"), as assignee and pledgee of the Burke Authority pursuant to the Trust Indenture, dated as of October 1, 2006 (the "Series 2006C-2 Burke Indenture"), between the Burke Authority and the Series 2006C-2 Burke Trustee;

         WHEREAS , the Company will use the proceeds from the sale of the Burke Bonds to refund the entire outstanding principal amount of the following series of bonds: (i) the Burke Authority's Pollution

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Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 1999A; (ii) the Burke Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 1999B; (iii) the Burke Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 2000; and the Burke Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series 2001, all to be redeemed on or before December 31, 2006;

Series 2006B Monroe Bonds

         WHEREAS, the Monroe Authority has agreed to issue $43,445,000 in aggregate principal amount of Development Authority of Monroe County Pollution Control Revenue Bonds (Oglethorpe Power Corporation Scherer Project), Series 2006B (the "Series 2006B Monroe Bonds"), and to loan the proceeds from the sale thereof to the Company pursuant to that certain Loan Agreement, dated as of October 1, 2006, relating thereto (the "Series 2006B Monroe Loan Agreement");

         WHEREAS, the Company's obligation to repay the loan of the proceeds of the Series 2006B Monroe Bonds is evidenced by that certain Series 2006B (Monroe) Note, dated the date of its authentication (the "Series 2006B (Monroe) Note"), from the Company to U.S. Bank National Association, as trustee (in such capacity, the "Series 2006B Monroe Trustee"), as assignee and pledgee of the Monroe Authority pursuant to the Trust Indenture, dated as of October 1, 2006 (the "Series 2006B Monroe Indenture"), between the Monroe Authority and the Series 2006B Monroe Trustee;

         WHEREAS , the Company will use the proceeds from the sale of the Series 2006B Monroe Bonds to refund the outstanding principal amount of the following series of bonds: (i) the Monroe Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Scherer Project), Series 1999A; (ii) the Monroe Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Scherer Project), Series 1999B; (iii) the Monroe Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Scherer Project), Series 2000; and (iv) the Monroe Authority's Pollution Control Revenue Bonds (Oglethorpe Power Corporation Scherer Project), Series 2001; all to be redeemed on or before December 31, 2006;

         WHEREAS, the Company desires to execute and deliver this Thirty-Seventh Supplemental Indenture, in accordance with the provisions of the Original Indenture, for the purpose of providing for the creation and designation of the Series 2006C-1 (Burke) Note, the Series 2006C-2 (Burke) Note and the Series 2006B (Monroe) Note (collectively, the "Notes") as Additional Obligations and specifying the form and provisions thereof;

         WHEREAS, Section 12.1 of the Original Indenture provides that, without the consent of the Holders of any of the Obligations, the Company, when authorized by a Board Resolution, and the Trustee, may enter into Supplemental Indentures for the purposes and subject to the conditions set forth in said Section 12.1, including to create additional series of Obligations under the Indenture and to make provisions for such additional series of Obligations; and

         WHEREAS, all acts and proceedings required by law and by the Articles of Incorporation and Bylaws of the Company necessary to secure under the Indenture the payment of the principal of (and premium, if any) and interest on the Notes, to make the Notes to be issued hereunder, when executed by the Company, authenticated and delivered by the Trustee and duly issued, the valid, binding and legal obligation of the Company, and to constitute the Indenture a valid and binding lien for the security of the Notes, in accordance with its terms, have been done and taken; and the execution and delivery of this Thirty-Seventh Supplemental Indenture has been in all respects duly authorized by the Company.

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         NOW, THEREFORE, THIS THIRTY-SEVENTH SUPPLEMENTAL INDENTURE WITNESSES , that, to secure the payment of the principal of (and premium, if any) and interest on the Outstanding Secured Obligations, including, when authenticated and delivered, the Notes, to confirm the lien of the Indenture upon the Trust Estate, including property purchased, constructed or otherwise acquired by the Company since the date of execution of the Original Indenture, to secure performance of the covenants therein and herein contained, to declare the terms and conditions on which the Notes are secured, and in consideration of the premises thereof and hereof, the Company by these presents does grant, bargain, sell, alienate, remise, release, convey, assign, transfer, mortgage, hypothecate, pledge, set over and confirm to the Trustee, and its successors and assigns in the trust created thereby and hereby, in trust, all property, rights, privileges and franchises (other than Excepted Property or Excludable Property) of the Company, whether now owned or hereafter acquired, of the character described in the Granting Clauses of the Original Indenture, wherever located, including all such property, rights, privileges and franchises acquired since the date of execution of the Original Indenture, including, without limitation, all property described in Exhibit A attached hereto, subject to all exceptions, reservations and matters of the character referred to in the Indenture, and does grant a security interest therein for the purposes expressed herein and in the Original Indenture subject in all cases to Sections 5.2 and 11.2 B of the Original Indenture and to the rights of the Company under the Original Indenture, including the rights set forth in Article V thereof; but expressly excepting and excluding from the lien and operation of the Indenture all properties of the character specifically excepted as "Excepted Property" or "Excludable Property" in the Original Indenture to the extent contemplated thereby.

         PROVIDED, HOWEVER , that if, upon the occurrence of an Event of Default, the Trustee, or any separate trustee or co-trustee appointed under Section 9.14 of the Original Indenture or any receiver appointed pursuant to statutory provision or order of court, shall have entered into possession of all or substantially all of the Trust Estate, all the Excepted Property described or referred to in Paragraphs A through H, inclusive, of "Excepted Property" in the Original Indenture then owned or thereafter acquired by the Company, shall immediately, and, in the case of any Excepted Property described or referred to in Paragraphs I, J, L, N and P of "Excepted Property" in the Original Indenture (excluding the property described in Section 2 of Exhibit B in the Original Indenture), upon demand of the Trustee or such other trustee or receiver, become subject to the lien of the Indenture to the extent permitted by law, and the Trustee or such other trustee or receiver may, to the extent permitted by law, at the same time likewise take possession thereof, and whenever all Events of Default shall have been cured and the possession of all or substantially all of the Trust Estate shall have been restored to the Company, such Excepted Property shall again be excepted and excluded from the lien of the Indenture to the extent and otherwise as hereinabove set forth and as set forth in the Indenture.

        The Company may, however, pursuant to the Granting Clause Third of the Original Indenture, subject to the lien of the Indenture any Excepted Property or Excludable Property, whereupon the same shall cease to be Excepted Property or Excludable Property.

         TO HAVE AND TO HOLD all such property, rights, privileges and franchises hereby and hereafter (by a Supplemental Indenture or otherwise) granted, bargained, sold, alienated, remised, released, conveyed, assigned, transferred, mortgaged, hypothecated, pledged, set over or confirmed as aforesaid, or intended, agreed or covenanted so to be, together with all the tenements, hereditaments and appurtenances thereto appertaining (said properties, rights, privileges and franchises, including any cash and securities hereafter deposited or required to be deposited with the Trustee (other than any such cash which is specifically stated in the Indenture not to be deemed part of the Trust Estate) being part of the Trust Estate), unto the Trustee, and its successors and assigns in the trust herein created by the Indenture, forever.

         SUBJECT, HOWEVER , to (i) Permitted Exceptions and (ii) to the extent permitted by Section 13.6 of the Original Indenture as to property hereafter acquired (a) any duly recorded or perfected prior

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mortgage or other lien that may exist thereon at the date of the acquisition thereof by the Company and (b) purchase money mortgages, other purchase money liens, chattel mortgages, conditional sales agreements or other title retention agreements created by the Company at the time of acquisition thereof.

         BUT IN TRUST, NEVERTHELESS , with power of sale, for the equal and proportionate benefit and security of the Holders from time to time of all the Outstanding Secured Obligations without any priority of any such Obligation over any other such Obligation and for the enforcement of the payment of such Obligations in accordance with their terms.

         UPON CONDITION that, until the happening of an Event of Default and subject to the provisions of Article V of the Original Indenture, and not in limitation of the rights elsewhere provided in the Original Indenture, including the rights set forth in Article V of the Original Indenture, the Company shall be permitted to (i) possess and use the Trust Estate, except cash, securities, Designated Qualifying Securities and other personal property deposited, or required to be deposited, with the Trustee, (ii) explore for, mine, extract, separate and dispose of coal, ore, gas, oil and other minerals, and harvest standing timber, and (iii) receive and use the rents, issues, profits, revenues and other income, products and proceeds of the Trust Estate.

         THE INDENTURE, INCLUDING THIS THIRTY-SEVENTH SUPPLEMENTAL INDENTURE, is intended to operate and is to be construed as a deed passing title to the Trust Estate and is made under the provisions of the laws of the State of Georgia relating to deeds to secure debt, and not as a mortgage or deed of trust, and is given to secure the Outstanding Secured Obligations. Should the indebtedness secured by the Indenture be paid according to the tenor and effect thereof when the same shall become due and payable and should the Company perform all covenants contained in the Indenture in a timely manner, then the Indenture shall be canceled and surrendered.

         AND IT IS HEREBY COVENANTED AND DECLARED that the Notes are to be authenticated and delivered and the Trust Estate is to be held and applied by the Trustee, subject to the covenants, conditions and trusts set forth herein and in the Indenture, and the Company does hereby covenant and agree to and with the Trustee, for the equal and proportionate benefit of all Holders of the Outstanding Secured Obligations, as follows:

ARTICLE I

THE NOTES AND CERTAIN PROVISIONS RELATING THERETO

Section 1.1    Authorization and Terms of the Notes.     

         A.     The Series 2006C-1 (Burke) Note     

        There shall be created and established an Additional Obligation in the form of a promissory note known as and entitled the "Series 2006C-1 (Burke) Note" (hereinafter referred to as the "Series 2006C-1 (Burke) Note"), the form, terms and conditions of which shall be substantially as set forth in or prescribed pursuant to this Section and Section 1.2 hereof. The aggregate principal amount of the Series 2006C-1 (Burke) Note which shall be authenticated and delivered and Outstanding at any one time is limited to $50,000,000.

        The Series 2006C-1 (Burke) Note shall be dated the date of its authentication. The Series 2006C-1 (Burke) Note shall mature on January 1, 2037 and shall bear interest from the date of its authentication to the date of its maturity at rates calculated as provided for in the form of note prescribed pursuant to Section 1.2 hereof. The Series 2006C-1 (Burke) Note shall be authenticated and delivered to, and made payable to, U.S. Bank National Association, as trustee, in its capacity as the Series 2006C-1 Burke Trustee.

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        All payments made on the Series 2006C-1 (Burke) Note shall be made to the Series 2006C-1 Burke Trustee at its principal office in Atlanta, Georgia in lawful money of the United States of America which will be immediately available on the date payment is due.

         B.     The Series 2006C-2 (Burke) Note     

        There shall be created and established an Additional Obligation in the form of a promissory note known as and entitled the "Series 2006C-2 (Burke) Note" (hereinafter referred to as the "Series 2006C-2 (Burke) Note"), the form, terms and conditions of which shall be substantially as set forth in or prescribed pursuant to this Section and Section 1.2 hereof. The aggregate principal amount of the Series 2006C-2 (Burke) Note which shall be authenticated and delivered and Outstanding at any one time is limited to $40,105,000.

        The Series 2006C-2 (Burke) Note shall be dated the date of its authentication. The Series 2006C-2 (Burke) Note shall mature on January 1, 2037 and shall bear interest from the date of its authentication to the date of its maturity at rates calculated as provided for in the form of note prescribed pursuant to Section 1.2 hereof. The Series 2006C-2 (Burke) Note shall be authenticated and delivered to, and made payable to, U.S. Bank National Association, as trustee, in its capacity as the Series 2006C-2 Burke Trustee.

        All payments made on the Series 2006C-2 (Burke) Note shall be made to the Series 2006C-2 Burke Trustee at its principal office in Atlanta, Georgia in lawful money of the United States of America which will be immediately available on the date payment is due.

         C.     The Series 2006B (Monroe) Note     

        There shall be created and established an Additional Obligation in the form of a promissory note known as and entitled the "Series 2006B (Monroe) Note" (hereinafter referred to as the "Series 2006B (Monroe) Note"), the form, terms and conditions of which shall be substantially as set forth in or prescribed pursuant to this Section and Section 1.2 hereof. The aggregate principal amount of the Series 2006B (Monroe) Note which shall be authenticated and delivered and Outstanding at any one time is limited to $43,445,000.

        The Series 2006