FORTIETH SUPPLEMENTAL INDENTURE

EXHIBIT 4.7.1(oo)

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

FORTIETH SUPPLEMENTAL
INDENTURE

Relating to the
Oglethorpe Power Corporation First Mortgage Bonds, Series 2007

Dated as of October 1, 2007

FIRST MORTGAGE OBLIGATIONS

NOTE TO THE CLERK OF THE SUPERIOR COURT AND TAX COMMISSIONER: BECAUSE THIS INSTRUMENT SECURES BONDS AND NOT A LONG TERM NOTE, THIS INSTRUMENT IS EXEMPT FROM THE INTANGIBLES RECORDING TAX PURSUANT TO GEORGIA ADMINISTRATIVE CODE §560-11-8-.14(d).

         THIS FORTIETH SUPPLEMENTAL INDENTURE , dated as of October 1, 2007, 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, 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;

         WHEREAS, the Company has heretofore executed and delivered to the Trustee thirty-nine Supplemental Indentures, and the Original Indenture and the thirty-nine Supplemental Indentures have been recorded as set forth on Schedule 1 ;

         WHEREAS, the Board of Directors of the Company has established a new series of Additional Obligations to be designated the First Mortgage Bonds, Series 2007, due January 1, 2031 in the principal amount of Five Hundred Million Dollars ($500,000,000) (the "Series 2007 Bonds") and the Company has complied or will comply with all provisions required to issue Additional Obligations provided for in the Original Indenture;

         WHEREAS, the Company desires to execute and deliver this Fortieth Supplemental Indenture, in accordance with the provisions of the Original Indenture, for the purpose of providing for the creation and designation of the Series 2007 Bonds as Additional Obligations and specifying the form and provisions thereof (the Original Indenture, as heretofore, hereby and hereafter supplemented and modified, being herein sometimes called the "Indenture");

         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 Series 2007 Bonds, to make the Series 2007 Bonds 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 Series 2007 Bonds, in accordance with its terms, have been done and taken; and the execution and delivery of this Fortieth Supplemental Indenture has been in all respects duly authorized by the Company;

         NOW, THEREFORE, THIS FORTIETH 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 Series 2007 Bonds, 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 Series 2007 Bonds 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, 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 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,

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(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 FORTIETH 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 Series 2007 Bonds 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

DEFINITIONS

Section 1.1     Definitions.

        All words and phrases defined in Article I of the Original Indenture shall have the same meaning in this Fortieth Supplemental Indenture, except as otherwise appears herein, in this Article I or unless the context clearly requires otherwise. In addition, the following terms have the following meaning in this Fortieth Supplemental Indenture unless the context clearly requires otherwise.

        " Closing Date " means October 3, 2007.

        " Interest Payment Date " means January 1 and July 1 of each year, commencing on January 1, 2008.

        " Record Date " means the 15th day (whether or not a Business Day) of the calendar month immediately preceding an Interest Payment Date.

        " Securities Depository " means The Depository Trust Company and its successors and assigns or any other securities depository selected by the Company which agrees to follow the procedures required to be followed by such securities depository in connection with the Series 2007 Bonds.

ARTICLE II

THE SERIES 2007 BONDS AND CERTAIN PROVISIONS RELATING THERETO

Section 2.1     Terms of the Series 2007 Bonds.

        There shall be established a series of Additional Obligations known as and entitled the "First Mortgage Bonds, Series 2007" (hereinafter referred to as the "Series 2007 Bonds").

        The aggregate principal amount of the Series 2007 Bonds which may be authenticated and delivered and Outstanding at any one time is limited to Five Hundred Million Dollars ($500,000,000). The Series 2007 Bonds shall consist of $500,000,000 principal amount of bonds, due January 1, 2031.

        The Series 2007 Bonds shall bear interest from their date of issuance, payable semi-annually on January 1 and July 1 of each year, commencing on January 1, 2008, at the rate of 6.191%. The principal and the Redemption Price of, and interest on, the Series 2007 Bonds shall be paid to the Person in whose name that Obligation (or one or more Predecessor Obligations) is registered at the

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close of business on the Record Date applicable to such Interest Payment Date or Redemption Date. Interest on the Series 2007 Bonds shall be computed on the basis of a 360-day year of twelve 30-day months. The Series 2007 Bonds shall be dated the date of authentication.

        The Series 2007 Bonds shall be issued as fully registered global bonds without coupons and in denominations of $100,000 or any integral multiple of $1,000 in excess thereof. The Series 2007 Bonds shall be registered in the name of Cede & Co., as nominee of the Securities Depository, pursuant to the Securities Depository's Book-Entry System. Purchases of beneficial interests in the Series 2007 Bonds shall be made in book-entry form, without certificates. If at any time the Book-Entry System is discontinued for the Series 2007 Bonds, the Series 2007 Bonds shall be exchangeable for other fully registered certificated Series 2007 Bonds of like tenor and of an equal aggregate principal amount, in authorized denominations. The Trustee may impose a charge sufficient to reimburse the Company or the Trustee for any tax, fee or other governmental charge required to be paid with respect to such exchange or any transfer of a Series 2007 Bond. The cost, if any, of preparing each new Series 2007 Bond issued upon such exchange or transfer, and any other expenses of the Company or the Trustee incurred in connection therewith, shall be paid by the person requesting such exchange or transfer.

        Interest on the Series 2007 Bonds shall be payable by check mailed to the registered owners thereof. However, interest on the Series 2007 Bonds shall be paid to any owner of $1,000,000 or more in aggregate principal amount of the Series 2007 Bonds by wire transfer to a wire transfer address within the continental United States upon the written request of such owner received by the Trustee not less than five days prior to the Record Date. As long as the Series 2007 Bonds are registered in the name of Cede & Co., as nominee of the Securities Depository, such payments shall be made directly to the Securities Depository.

Section 2.2     Sinking Fund Redemption.

        (a)   The Series 2007 Bonds will be redeemed, on a pro rata basis, in multiples of $100,000, through the operation of a mandatory sinking fund, commencing on January 1, 2024, and continuing on January 1 in each year afterwards to, and including, January 1, 2030, upon not less than 30 nor more than 60 days' notice mailed to each Holder of Series 2007 Bonds being redeemed at the Holder's registered address, except as otherwise required by the procedures of the Securities Depository. The sinking fund redemption price will be equal to 100% of the principal amount of the Series 2007 Bonds being redeemed plus accrued interest to the Redemption Date, including interest due on an Interest Payment Date that is on, or prior to, the Redemption Date. The principal amount of the Series 2007 Bonds being redeemed and the Redemption Dates, as well as the principal amount payable on the maturity date, are set forth below.

• • ---

    (1)

    The final maturity date of the Series 2007 Bonds.

        (b)   The Series 2007 Bonds that the Company acquires and surrenders for cancellation or redemption (other than by means of sinking fund redemptions) will be credited against future sinking

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fund payments for such Series 2007 Bonds and the principal payment to be made on the maturity date of such Series 2007 Bonds, in proportion to the respective amounts of those sinking fund and principal payments, subject to authorized denominations.

Section 2.3     Make Whole Redemption.

        (a)   The Company may redeem the Series 2007 Bonds, in whole or in part, on any date prior to their maturity, at its option. The Company must give at least 30 days, but not more than 60 days, prior notice of redemption mailed to the registered address of each Holder of Series 2007 Bonds being redeemed except as otherwise required by the procedures of the Securities Depository. The Redemption Price for the Series 2007 Bonds will be equal to the greater of:

• •

  100% of the principal amount of the Series 2007 Bonds being redeemed plus interest accrued through the Redemption Date; and
  
  

  •

  the sum of the present values of the remaining principal and interest payments on the Series 2007 Bonds being redeemed, discounted on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at a rate equal to the sum of (1) the yield to maturity of the U.S. Treasury security having a life equal to the remaining average life of the maturity of Series 2007 Bonds being redeemed and trading in the secondary market at the price closest to par, and (2) 20 basis points.

        (b)   If there is no U.S. Treasury security having a life equal to the remaining average life of the Series 2007 Bonds being redeemed, the discount rate will be calculated using a yield to maturity determined on a straight-line basis (rounding to the nearest calendar month, if necessary) from the average yield to maturity of two U.S. Treasury securities having lives most closely corresponding to the remaining average life of the Series 2007 Bonds being redeemed and trading in the secondary market at the price closest to par.

        (c)   If less than all of the Outstanding Series 2007 Bonds are to be redeemed, the Series 2007 Bonds to be redeemed will be selected by the Trustee in any method it deems fair and appropriate and the portion of the Series 2007 Bonds not so redeemed will be in multiples of $100,000.

        (d)   If the Company gives notice of the optional redemption of the Series 2007 Bonds but the Trustee does not have enough funds on deposit to pay the full Redemption Price of the Series 2007 Bonds to be redeemed, those Series 2007 Bonds will remain Outstanding as though no redemption notice had been given. The failure of the Trustee to have sufficient funds to effect the redemption will not constitute a payment or other default by the Company under the Indenture and the Company will not be liable to any Holder of those Series 2007 Bonds as a result of the failed redemption. If the Trustee has enough funds on deposit to effect a redemption at the time the Company gives notice of the redemption, then the Company is obligated to redeem the Series 2007 Bonds as provided in that notice.

Section 2.4     Form of the Series 2007 Bonds.     The Series 2007 Bonds and the Trustee's authentication certificate to be executed on the Series 2007 Bonds shall be substantially in the form of Exhibit A attached hereto, with such appropriate insertions, omissions, substitutions and other variations as are required or permitted in the Original Indenture.

Section 2.5     Use of Proceeds.     The Company expects the proceeds of this offering of the Series 2007 Bonds, net of the initial purchasers' discounts and offering expenses, including the premium to FSA (as defined below) to be $491,010,069.38. The Company will use the net proceeds of this offering to prepay a portion of the indebtedness outstanding under the Indenture owed to the Federal Financing Bank (the "FFB") and guaranteed by the United States of America, acting by and through the Administrator of the Rural Utilities Service, totaling approximately $454,000,000, and for other general purposes,

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including the payment of premiums associated with the prepayment of the FFB debt and offering expenses associated with the issuance of the Series 2007 Bonds.

Section 2.6     Financial Security Assurance Inc. Designated Credit Enhancer.     Financial Security Assurance Inc., a New York stock insurance company ("FSA"), or any successor thereto or assignee thereof, is hereby designated the Credit Enhancer with resp