Document:

<PAGE>

                                                                EXHIBIT 4.7.1(k)

                                                      UPON RECORDING, RETURN TO:
                                                            MS. SHAWNE M. KEENAN
                                                 SUTHERLAND ASBILL & BRENNAN LLP
                                                      999 PEACHTREE STREET, N.E.
                                                     ATLANTA, GEORGIA 30309-3996

   PURSUANT TO SECTION 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

                             SUNTRUST BANK, ATLANTA,
                                     TRUSTEE

                               TENTH SUPPLEMENTAL
                                    INDENTURE

                                 Relating to the
                             Series 1999 Lease Notes

                          Dated as of December 1, 1999

                           FIRST MORTGAGE OBLIGATIONS

================================================================================
================================================================================

<PAGE>

        THIS TENTH SUPPLEMENTAL INDENTURE, dated as of December 1, 1999, is
between OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION), an
electric membership corporation organized and existing under the laws of the
State of Georgia, as Grantor (hereinafter called the "Company"), and SUNTRUST
BANK, ATLANTA, a banking corporation organized and existing under the laws of
the State of Georgia, 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 entered into a Participation Agreement, dated
as of December 29, 1999 (the "Participation Agreement"), among itself, First
Security Bank, National Association, a national banking organization, as Owner
Trustee, Pitney Bowes Credit Corporation, a Delaware corporation, as Trustor,
Black Diamond Energy, Inc., a Georgia corporation, as Seller, and CoBank, ACB,
as Lender, pursuant to which the parties are engaging in a transaction involving
the lease by the Owner Trustee of certain open top hopper railcars to the
Company (capitalized terms used herein and not otherwise defined herein shall
have the meanings ascribed to them in the Original Indenture as provided in
Section 2.1 hereof, or if not defined in the Original Indenture, shall have the
meanings ascribed to them in the Glossary attached as Exhibit B to the
Participation Agreement, except, in cases where the context clearly indicates
otherwise);

        WHEREAS, pursuant to Section 3.2(b) of the Participation Agreement, the
Company is required to issue Series 1999 Lease Notes at each closing to support
certain of the Company's obligations under the Lease to pay Casualty Loss Value
and Make Whole Premium Amount upon an Event of Default under the Lease;

        WHEREAS, the Company desires to execute and deliver this Tenth
Supplemental Indenture, in accordance with the provisions of the Original
Indenture, for the purpose of providing for the creation and designation of the
Series 1999 Lease Notes as Additional Obligations and specifying the form and
provisions of the Series 1999 Lease Notes (the Original Indenture, as
heretofore, hereby and hereafter supplemented and modified, being herein
sometimes called the "Indenture");

        WHEREAS, the Series 1999 Lease Notes are to be authenticated and
delivered pursuant to Section 4.3 of the Original Indenture upon the basis of
retirement of Obligations;

        WHEREAS, Section 12.1 of the Original Indenture provides that, without
the consent of the Holders of any of the Obligations at the time Outstanding,
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; 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

<PAGE>

premium, if any) and interest on the Series 1999 Lease Notes, to make the Series
1999 Lease Notes to be issued hereunder, when executed by the Company,
authenticated and delivered by the Trustee and duly issued, the valid, binding
and legal obligations of the Company, and to constitute the Indenture a valid
and binding lien for the security of the Series 1999 Lease Notes, in accordance
with its terms, have been done and taken; and the execution and delivery of this
Tenth Supplemental Indenture has been in all respects duly authorized;

        NOW, THEREFORE, THIS TENTH 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 issued, the Series 1999
Lease 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 Series 1999 Lease 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 of the character described in the Granting Clauses of the
Original Indenture, 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 Original
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.

                                        2

<PAGE>

        TO HAVE AND TO HOLD all such property, rights, privileges and franchises
hereby and hereafter (by 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, 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, (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 TENTH 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 existing 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 herein contained in a timely manner, then the Indenture
shall be canceled and surrendered.

        AND IT IS HEREBY COVENANTED AND DECLARED that the Series 1999 Lease
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 Original 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:

                                        3

<PAGE>

                                    ARTICLE I

                         THE SERIES 1999 LEASE NOTES AND
                       CERTAIN PROVISIONS RELATING THERETO

        SECTION 1.1   AUTHORIZATION AND TERMS OF THE SERIES 1999 LEASE NOTE.

        There shall be created and established a series of Additional Obligation
in the form of promissory notes known as and entitled the "Series 1999 Lease
Notes" (hereinafter referred to as the "Series 1999 Lease Notes"), the form,
terms and conditions of which shall be substantially as set forth in this
Section and Section 1.2.

        The Series 1999 Lease Notes shall be issuable in fully registered form
without coupons and in denominations necessary to issue Series 1999 Lease Notes
in the principal amounts required pursuant to Section 3 of the Participation
Agreement; PROVIDED that the aggregate principal amount payable at any one time
under the Series 1999 Lease Notes shall not exceed $13,500,000. Each Series 1999
Lease Note shall be dated the date of its authentication.

        For purposes of (i) receiving payment upon any Series 1999 Series Lease
Note, whether when due pursuant to the terms thereof or if the principal of all
Obligations is declared immediately due and payable following an Event of
Default as provided in Section 8.1 of the Indenture, or (ii) computing the
principal amount of Obligations held by any Holder of such Series 1999 Lease
Note in giving any request, demand, authorization, direction, notice, consent,
waiver or other action provided by the Indenture to be given or taken by
Holders, the principal amount of such Series 1999 Lease Note shall be the actual
Secured Amount then due and payable on the Series 1999 Lease Note at such time.
For the purposes of serving as the basis for authenticating and delivering
Additional Obligations under Section 4.3 of the Original Indenture the principal
amount of any Series 1999 Lease Note shall be the highest Secured Amount set
forth on Annex A to such Series 1999 Lease Note.

        Except in the event that the principal of the Series 1999 Lease Notes
shall not be paid when due or shall be declared due and payable in the manner
and with the effect provided in Section 8.2 of the Original Indenture, the
Series 1999 Lease Notes shall not bear interest. In the event that the principal
of the Series 1999 Lease Notes shall not be paid when due or shall be declared
due and payable in the manner and with the effect provided in Section 8.2 of the
Original Indenture, the Series 1999 Lease Notes shall bear interest on the
principal amount thereof from the date due or the date of such declaration, as
the case may be, at the Overdue Rate. Any such interest shall be payable
concurrently with the payment of the principal of such Series 1999 Lease Notes.

        Each Series 1999 Lease Note shall expire and be deemed to have been
cancelled upon the earlier of (i) the expiration or early termination of the
Lease with respect to all Units listed on the applicable Lease Supplement and
(x) if and to the extent required pursuant thereto, the return of such Units to
the Lessor pursuant to the terms and provisions of the Lease and (y) the making
of all payments required to be made by the Company in connection with the
expiration or early termination of the Lease with respect to such Units, and
(ii) payment of all amounts then due and payable on this Series 1999 Lease Note
following the Secured Amount becoming due and payable thereunder.

                                        4

<PAGE>

        All payments made on the Series 1999 Lease Notes shall be made in lawful
money of the United States of America to such address as the Holder thereof
shall direct, from time to time, by written notice to the Company and the
Trustee.

        SECTION 1.2   FORM OF THE SERIES 1999 LEASE NOTES.

        The Series 1999 Lease Notes, including the Trustee's authentication
certificate to be executed on such Notes, 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. The Series 1999A Lease Notes shall be numbered from 1 consecutively
upwards in order of issuance hereunder or shall have such other designation and
numbers as the Company may determine.

        SECTION 1.3 DESIGNATION OF AMBAC ASSURANCE CORPORATION AS CREDIT
ENHANCER FOR THE SERIES 1999 LEASE NOTES.

        In accordance with the provisions of the Original Indenture, Ambac
Assurance Corporation is hereby designated as the "Credit Enhancer" for the
Series 1999 Lease Notes, as such term is defined in Section 1.1 of the Original
Indenture.

                                   ARTICLE II

                                  MISCELLANEOUS

        SECTION 2.1 This Tenth Supplemental Indenture is executed and shall be
construed as an indenture supplemental to the Original Indenture, and shall form
a part thereof, and the Indenture, as heretofore supplemented and as hereby
supplemented and modified, is hereby confirmed. Except to the extent
inconsistent with the express terms hereof, all of the provisions, terms,
covenants and conditions of the Indenture shall be applicable to the Series 1999
Lease Notes to the same extent as if specifically set forth herein. All
references herein to Sections, definitions or other provisions of the Original
Indenture shall be to such Sections, definitions and other provisions as they
may be amended or modified from time to time pursuant to the Indenture. All
capitalized terms used in this Tenth Supplemental Indenture and not otherwise
defined herein shall have the same meanings ascribed to them in the Original
Indenture, or if not defined in the Original Indenture, the meanings ascribed to
them in the Glossary attached as Exhibit B to the Participation Agreement,
except, in cases where the context clearly indicates otherwise.

        SECTION 2.2 All recitals in this Tenth Supplemental Indenture are made
by the Company only and not by the Trustee; and all of the provisions contained
in the Original Indenture, in respect of the rights, privileges, immunities,
powers and duties of the Trustee shall be applicable in respect hereof as fully
and with like effect as if set forth herein in full.

        SECTION 2.3 Whenever in this Tenth Supplemental Indenture any of the
parties hereto is named or referred to, this shall, subject to the provisions of
Articles IX and XI of the Original Indenture, be deemed to include the
successors and assigns of such party, and all the covenants and Agreements in
this Tenth Supplemental Indenture contained by or on behalf of the Company, or
by or on behalf of

                                        5

<PAGE>

the Trustee shall, subject as aforesaid, bind and inure to the respective
benefits of the respective successors and assigns of such parties, whether so
expressed or not.

        SECTION 2.4 Nothing in this Tenth Supplemental Indenture, expressed or
implied, is intended, or shall be construed, to confer upon, or to give to, any
person, firm or corporation, other than the parties hereto and the Holders of
the Outstanding Secured Obligations, any right, remedy or claim under or by
reason of this Tenth Supplemental Indenture or any covenant, condition,
stipulation, promise or agreement hereof, and all the covenants, conditions,
stipulations, promises and agreements in this Tenth Supplemental Indenture
contained by or on behalf of the Company shall be for the sole and exclusive
benefit of the parties hereto, and of the Holders of Outstanding Secured
Obligations.

        SECTION 2.5 This Tenth Supplemental Indenture may be executed in several
counterparts, each of such counterparts shall for all purposes be deemed to be
an original, and all such counterparts, or as many of them as the Company and
the Trustee shall preserve undestroyed, shall together constitute but one and
the same instrument.

        SECTION 2.6 To the extent permitted by applicable law, this Tenth
Supplemental Indenture shall be deemed to be a Security Agreement and Financing
Statement whereby the Company grants to the Trustee a security interest in all
of the Trust Estate that is personal property or fixtures under the Uniform
Commercial Code, as adopted or hereafter adopted in one or more of the states in
which any part of the properties of the Company are situated. The mailing
address of the Company,

as debtor is:                2100 East Exchange Place
                             P.0. Box 1349
                             Tucker, Georgia 30085-1349,

and the mailing address of the Trustees, as secured party is:

                             SunTrust Bank, Atlanta
                             25 Park Place
                             Atlanta, Georgia 30303-2900

                                  [Signatures on Next Page.]

                                        6

<PAGE>

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

COMPANY:                              OGLETHORPE POWER
                                      CORPORATION (AN ELECTRIC MEMBERSHIP
                                      CORPORATION), an electric membership
                                      corporation organized under the laws
                                      of the State of Georgia

2100 East Exchange Place
P.O. Box 1349
Tucker, Georgia 30085-1349

                                      By: /s/ THOMAS A. SMITH
                                          -----------------------------------
                                          Thomas A. Smith
                                          President and Chief Executive Officer

Signed, sealed and delivered          Attest: /s/ PATRICIA N. NASH
by the Company in the presence of          ----------------------------------
                                           Patricia N. Nash
                                           Secretary

/s/ LYNN H. LESTER
----------------------------------
Witness

/s/ MELONEY A. CHENENEY
----------------------------------
Notary Public

(Notarial Seal)

My commission expires:   OCTOBER 20, 2000
                      -----------------------

                       [Signatures Continued on Next Page]

                                        7

<PAGE>

                   [Signatures Continued from Previous Page.]

TRUSTEE:                            SUNTRUST BANK, ATLANTA,
                                    a banking corporation organized and existing
                                    under the laws of the State of Georgia

Signed, sealed and delivered
by the trustee in the               By: /s/ BARTON A. DONALDSON
presence of:                            ----------------------------------
                                        Barton A. Donaldson
                                        Vice President

/s/ CADA T. KILGORE
--------------------------------
Witness

/s/ TERESA R. TURNER
--------------------------------
Notary Public

(Notarial Seal)                                    [BANK SEAL]

My commission expires:       APRIL 3, 2001
                       ----------------------

                                        8

<PAGE>

                                    EXHIBIT A

                        [Form of Series 1999 Lease Note]

Financial Guaranty Insurance Policy No. [ ] (the "Policy") with respect to
payments due for principal of and interest on this note has been issued by Ambac
Assurance Corporation ("Ambac Assurance"). All payments required to be made
under the Policy shall be made in accordance with the provisions thereof. The
owner of this note acknowledges and consents to the subrogation rights of Ambac
Assurance as more fully set forth in the Policy.

    THIS SERIES 1999 LEASE NOTE HAS NOT BEEN AND WILL NOT BE REGISTERED UNDER
      THE SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD, OFFERED
             FOR SALE OR OTHERWISE TRANSFERRED WITHOUT REGISTRATION
                UNDER SUCH ACT OR IN RELIANCE UPON AN APPLICABLE
                   EXEMPTION FROM REGISTRATION UNDER SUCH ACT.

                          OGLETHORPE POWER CORPORATION
                      (AN ELECTRIC MEMBERSHIP CORPORATION)

                             SERIES 1999 LEASE NOTE

No.                                                                        DATE:

     OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION) (the
"Company"), an electric membership corporation organized and existing under the
laws of the State of Georgia, for value received hereby promises to pay to
[_______________] or its registered assigns, as principal due and payable
hereunder an amount equal to the [Casualty Loss Value] [Make Whole Premium
Amount] payable under Section [18.1.][18.2.] of the Equipment Lease Agreement,
dated as of December 29, 1999 (the "Lease"), between the Company and First
Security Bank, National Association, a national banking association, not in its
individual capacity, but solely as trustee under the Owner Trust Agreement,
dated as of December 29, 1999, with Pitney Bowes Credit Corporation (in such
capacity, the "Owner Trustee") for [the Loan Certificates relating to] the Units
listed on Schedule 1 to Lease Supplement No. [__] thereto [(the "Casualty Loss
Value")][(the "Make Whole Premium Amount")]; PROVIDED, HOWEVER, in no event
shall the principal amount payable hereunder (the "Secured Amount") exceed the
amount set forth on Annex A hereto for the date [Casualty Loss Value][the Make
Whole Premium Amount] becomes due and payable under Section [18.1][18.2] of the
Lease. The Secured Amount shall be due and payable at any time after [the
earlier of (i) the date Lender transfers the Loan Certificates to Trustor or
Lessor pursuant to Section 2.13 of the Loan Agreement or (ii) the date] the
Casualty Loss Value becomes due and payable pursuant to Section 18.1. of the
Lease [or is declared due and payable pursuant to the clause (ix) of Section
18.1.(b)] of the Lease, unless[, in either case,] payment of [Casualty Loss
Value][the Make Whole Premium Amount] is made in full under the Lease prior to
such time. In the event the Secured Amount becomes payable as provided in the
foregoing sentence, the Secured Amount shall bear interest at the Overdue Rate
(as

                                       A-1

<PAGE>

defined in or pursuant to the Lease) from the date when payable to the date of
payment by the Company hereunder or under the Lease.

        For purposes of (i) receiving payment upon this Series 1999 Lease Note,
whether at when due pursuant to the preceding paragraph or if the principal of
all Obligations is declared immediately due and payable following an Event of
Default as provided in Section 8.1 of the Indenture, or (ii) computing the
principal amount of Obligations held by any Holder of this Series 1999 Lease
Note in giving any request, demand, authorization, direction, notice, consent,
waiver or other action provided by the Indenture to be given or taken by
Holders, the principal amount of this Series 1999 Lease Note shall be the actual
Secured Amount then due and payable on this Series 1999 Lease Note at such time.
For the purposes of serving as the basis for authenticating and delivering
Additional Obligations under Section 4.3 of the Original Indenture the principal
amount of this Series 1999 Lease Note shall be $[______] [fill in the highest
amount set forth on Annex A].

        Except in the event that the principal of this Series 1999 Lease Note
shall not be paid when due or shall be declared due and payable in the manner
and with the effect provided in Section 8.2 of the Indenture, this Series 1999
Lease Note shall not bear interest. In the event that the principal of this
Series 1999 Lease Note shall not be paid when due or shall be declared due and
payable in the manner and with the effect provided in Section 8.2 of the
Original Indenture, this Series 1999 Lease Note shall bear interest on the
principal amount thereof from the date due or the date of such declaration, as
the case may be, at the Overdue Rate. Any such interest shall be payable
concurrently with the payment of the principal of this Series 1999 Lease Note.

        This Series 1999 Lease Note is a duly authorized obligation of the
Company issued under and equally and ratably secured by the Indenture, dated as
of March 1, 1997 (the "Original Indenture"), between the Company, as grantor,
and SunTrust Bank, Atlanta, as trustee (in such capacity, the "Indenture
Trustee"), as supplemented by the First Supplemental Indenture, dated as of
October 1, 1997, the Second Supplemental Indenture, dated as of January 1, 1998,
the Third Supplemental Indenture, dated as of January 1, 1998, the Fourth
Supplemental Indenture, dated as of March 1, 1998, the Fifth Supplemental
Indenture, dated as of April 1, 1998, the Sixth Supplemental Indenture, dated as
of January 1, 1999, the Seventh Supplemental Indenture, dated as of January 1,
1999, the Eighth Supplemental Indenture, dated as of November 1, 1999, the Ninth
Supplemental Indenture, dated as of November 1, 1999, and the Tenth Supplemental
Indenture, dated as of December 1, 1999 (the "Tenth Supplemental Indenture")
between the Company and the Indenture Trustee (the Original Indenture, as
supplemented, the "Indenture"). Reference is hereby made to the Indenture for a
statement of the description of the properties thereby mortgaged, pledged and
assigned, the nature and extent of the security and the respective rights,
limitations of rights, duties and immunities thereunder of the Company, the
Indenture Trustee and the holder of this Series 1999 Lease Note and of the terms
upon which this Series 1999 Lease Note is authenticated and delivered. This
Series 1999 Lease Note is created by the Tenth Supplemental Indenture and
designated as the "Series 1999 Lease Note."

        All payments hereon are to be made in lawful money of the United States
of America to such address as the Holder of this Series 1999 Lease Note shall
direct, from time to time, by written notice to the Company and the Trustee.

                                       A-2

<PAGE>

        No recourse shall be had for the payments required hereby or for any
claim based herein or in the Lease or in the Indenture against any officer,
director or member, past, present or future, of the Company as such, either
directly or through the Company, or under any constitution provision, statute or
rule of law or by the enforcement of any assessment or by any legal or equitable
proceedings or otherwise.

        This Series 1999 Lease Note shall not be entitled to any benefit under
the Indenture and shall not become valid or obligatory for any purposes until
the Indenture Trustee shall have signed the form of authentication certificate
endorsed hereon.

        This Series 1999 Lease Note shall expire and be deemed to have been
cancelled upon the earlier of (i) the expiration or early termination of the
Lease with respect to all Units listed on Schedule 1 to the Lease Supplement No.
[___] dated as of [_____], between the Company and the Owner Trustee [identify
Lease Supplement] and (x) if and to the extent required pursuant thereto, the
return of such Units to the Owner Trustee pursuant to the terms and provisions
of the Lease and (y) the making of all payments required to be made by the
Company in connection with the expiration or early termination of the Lease with
respect to the Units, and (ii) payment of all amounts then due and payable on
this Series 1999 Lease Note following the Secured Amount becoming due and
payable hereunder.

        This Series 1999 Lease Note shall be governed by and construed in
accordance with the laws of the State of Georgia.

                                       A-3

<PAGE>

        IN WITNESS WHEREOF, the Company has caused this Series 1999 Lease Note
to be duly executed in its corporate name by its President and Chief executive
Officer and attested by its Secretary and its corporate seal to be hereunto
affixed.

Dated:

                                         OGLETHORPE POWER CORPORATION
                                           (AN ELECTRIC MEMBERSHIP
                                            CORPORATION)

                                         By:
                                            ------------------------------------
                                            Name:
                                            Title:

ATTEST:

----------------------------------
Name:
Title:

                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION

        This is one of the Obligations of the series designated therein referred
to in the within-mentioned Indenture.

                                         SUNTRUST BANK, ATLANTA,
                                         as Trustee

                                         By:
                                           -------------------------------------
                                                Authorized Signatory

                                       A-4

<PAGE>

                                     ANNEX A

                                 SECURED AMOUNT

               Period during which
               Casualty Loss Value
               becomes
               due and payable                     Secured Amount
               ----------------------              --------------

                                       A-5<PAGE>

                                                                EXHIBIT 4.7.1(l)

                                                      UPON RECORDING, RETURN TO:
                                                            MS. SHAWNE M. KEENAN
                                                 SUTHERLAND ASBILL & BRENNAN LLP
                                                      999 PEACHTREE STREET, N.E.
                                                     ATLANTA, GEORGIA 30309-3996

   PURSUANT TO SECTION 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

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================================================================================

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

                                       to

                                 SUNTRUST BANK,
                                     TRUSTEE

                              ELEVENTH SUPPLEMENTAL
                                    INDENTURE

                                 Relating to the
                            Series 1999A (Burke) Note

                           Dated as of January 1, 2000

                           FIRST MORTGAGE OBLIGATIONS

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================================================================================

<PAGE>

     THIS ELEVENTH SUPPLEMENTAL INDENTURE, dated as of January 1, 2000, is
between OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION), an
electric membership corporation organized and existing under the laws of the
State of Georgia, as Grantor (hereinafter called the "Company"), and SUNTRUST
BANK, formerly known as SunTrust Bank, Atlanta, a banking corporation organized
and existing under the laws of the State of Georgia, 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
shall have the meanings ascribed to them in the Original Indenture as provided
in Section 2.1 hereof);

     WHEREAS, the Development Authority of Burke County (the "Burke Authority")
issued $199,690,000 in aggregate principal amount of Development Authority of
Burke County Adjustable Tender Pollution Control Revenue Bonds (Oglethorpe Power
Corporation Vogtle Project), Series 1993A (the "Series 1993A Bonds"), of which
$2,595,000 in principal amount is subject to mandatory sinking fund redemption
on January 1, 2000 (the "1993A Sinking Fund Maturities");

     WHEREAS, the Burke Authority loaned the proceeds from the sale of the
Series 1993A Bonds to the Company, with such loan being evidenced by that
certain Series 1993A Note, dated as of December 1, 1992 (the "Series 1993A
Note"), from the Company to SunTrust Bank, formerly known as Trust Company Bank,
as trustee (in such capacity, the "Series 1993A Trustee"), as assignee and
pledgee of the Burke Authority pursuant to the Trust Indenture, dated as of
December 1, 1992 (the "Series 1993A Indenture"), between the Burke Authority and
the Series 1993A Trustee;

     WHEREAS, the Burke Authority issued $155,610,000 in aggregate principal
amount of Development Authority of Burke County Pollution Control Revenue Bonds
(Oglethorpe Power Corporation Vogtle Project), Series 1993B (the "Series 1993B
Bonds"), of which $7,770,000 in aggregate principal amount matures on January 1,
2000 (the "1993B Maturities");

     WHEREAS, the Burke Authority loaned the proceeds from the sale of the
Series 1993B Bonds to the Company, with such loan being evidenced by that
certain Series 1993B Note, dated as of September 1, 1993 (the "Series 1993B
Note"), from the Company to SunTrust Bank, formerly known as Trust Company Bank,
as trustee (in such capacity, the "Series 1993B Trustee"), as assignee and
pledgee of the Burke Authority pursuant to the Trust Indenture, dated as of
September 1, 1993 (the "Series 1993B Indenture"), between the Burke Authority
and the Series 1993B Trustee;

<PAGE>

     WHEREAS, the Burke Authority issued $122,740,000 in aggregate principal
amount of Development Authority of Burke County Adjustable Tender Pollution
Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series
1994A (the "Series 1994A Bonds"), of which $2,240,000 in aggregate principal
amount is subject to mandatory sinking fund redemption on January 1, 2000 (the
"1994A Sinking Fund Maturities");

     WHEREAS, the Burke Authority loaned the proceeds from the sale of the
Series 1994A Bonds to the Company, with such loan being evidenced by that
certain Series 1994A Note, dated as of December 1, 1992 (the "Series 1994A
Note"), from the Company to SunTrust Bank, formerly known as Trust Company Bank,
as trustee (in such capacity, the "Series 1994A Trustee"), as assignee and
pledgee of the Burke Authority pursuant to the Trust Indenture, dated as of
December 1, 1992 (the "Series 1994A Indenture"), between the Burke Authority and
the Series 1994A Trustee;

     WHEREAS, the Burke Authority issued $13,720,000 in aggregate principal
amount of Development Authority of Burke County Pollution Control Revenue Bonds
(Oglethorpe Power Corporation Vogtle Project), Series 1994B (the "Series 1994B
Bonds"; the Series 1993A Bonds, the Series 1993B Bonds, the Series 1994A Bonds
and the Series 1994B Bonds, collectively, the "Outstanding Bonds"), of which
$1,540,000 in aggregate principal amount matures on January 1, 2000 (the "1994B
Maturities"; the 1993A Sinking Fund Maturities, the 1993B Maturities, the 1994A
Sinking Fund Maturities and the 1994B Maturities, collectively, the "2000
Maturities");

     WHEREAS, the Burke Authority loaned the proceeds from the sale of the
Series 1994B Bonds to the Company, with such loan being evidenced by that
certain Series 1994B Note, dated as of September 1, 1994 (the "Series 1994B
Note"; the Series 1993A Note, the Series 1993B Note, the Series 1994A Note and
the Series 1994B Note, collectively, the "Outstanding Notes"), from the Company
to SunTrust Bank, formerly known as Trust Company Bank, as trustee (in such
capacity, the "Series 1994B Trustee"), as assignee and pledgee of the Burke
Authority pursuant to the Trust Indenture, dated as of September 1, 1994 (the
"Series 1994B Indenture"), between the Burke Authority and the Series 1994B
Trustee;

     WHEREAS, on November 17, 1999, the Burke Authority issued $14,145,000 in
aggregate principal amount of Development Authority of Burke County Pollution
Control Revenue Bonds (Oglethorpe Power Corporation Vogtle Project), Series
1999A (the "Series 1999A (Burke) Bonds"), the proceeds from the sale of which
were loaned to the Company pursuant to that certain Loan Agreement, dated as of
November 1, 1999 (the "Series 1999A (Burke) Loan Agreement"), between the Burke
Authority and the Company to refund the 2000 Maturities and to make the related
payments due on the Outstanding Notes;

     WHEREAS, the Company's obligation to repay the loan of the proceeds of the
Series 1999A (Burke) Bonds is evidenced by that certain Series 1999A (Burke)
Note, dated November 17, 1999 (the "Unsecured Note"), from the Company to
SunTrust Bank, formerly known as SunTrust Bank, Atlanta, as trustee (in such
capacity, the "Series 1999A (Burke) Trustee"), as assignee and pledgee

                                       2
<PAGE>

of the Burke Authority pursuant to the Trust Indenture, dated as of November 1,
1999 (the "Series 1999A (Burke) Indenture"), between the Burke Authority and the
Series 1999A (Burke) Trustee;

     WHEREAS, as permitted by Section 4.9 of the Series 1999A (Burke) Loan
Agreement, the Company desires to deliver to the Series 1999A (Burke) Trustee a
promissory note secured under the Indenture (as hereinafter defined) in
substitution for the Unsecured Note;

     WHEREAS, the Company desires to execute and deliver this Eleventh
Supplemental Indenture, in accordance with the provisions of the Original
Indenture, for the purpose of providing for the creation and designation of that
certain Series 1999A (Burke) Note, dated the date of its authentication (the
"Series 1999A (Burke) Note"), from the Company to the Series 1999A (Burke)
Trustee, as assignee and pledgee of the Burke Authority pursuant to the Series
1999A (Burke) Indenture, as an Additional Obligation 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, pursuant to Section 4.9 of the Series 1999A (Burke) Loan
Agreement, upon the authentication of the Series 1999A (Burke) Note by the
Trustee, the Series 1999A (Burke) Note will be delivered to the Series 1999A
(Burke) Trustee in substitution for the Unsecured Note;

     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;
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
1999A (Burke) Note, to make the Series 1999A (Burke) Note 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 1999A (Burke) Note, in accordance with its terms, have been done and
taken; and the execution and delivery of this Eleventh Supplemental Indenture
has been in all respects duly authorized by the Company;

     NOW, THEREFORE, THIS ELEVENTH 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 issued, the Series 1999A
(Burke) Note, 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 1999A (Burke) Note is 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

                                       3
<PAGE>

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 of the character described in the Granting
Clauses of the Original Indenture, 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 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, forever.

                                       4
<PAGE>

     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, (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 ELEVENTH 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 existing 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 therein contained in a timely manner, then the Indenture shall be
canceled and surrendered.

     AND IT IS HEREBY COVENANTED AND DECLARED that the Series 1999A (Burke) Note
is 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
olders of the Outstanding Secured Obligations, as follows:

                                       5
<PAGE>

                                    ARTICLE I

                        THE SERIES 1999A (BURKE) NOTE AND
                       CERTAIN PROVISIONS RELATING THERETO

      SECTION 1.1 AUTHORIZATION AND TERMS OF THE SERIES 1999A (BURKE) NOTE.

     There shall be created and established an Additional Obligation in the form
of a promissory note known as and entitled the "Series 1999A (Burke) Note"
(hereinafter referred to as the "Series 1999A (Burke) Note"), the form, terms
and conditions of which shall be substantially as set forth in this Section and
Section 1.2. The aggregate principal face amount of the Series 1999A (Burke)
Note which shall be authenticated and delivered and Outstanding at any one time
is limited to $14,145,000.

     The Series 1999A (Burke) Note shall be dated the date of its
authentication. The Series 1999A (Burke) Note shall mature on January 1, 2020
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 by
Section 1.2. The Series 1999A (Burke) Note shall be authenticated and delivered
to, and made payable to, SunTrust Bank, Atlanta, as trustee, in its capacity as
the Series 1999A (Burke) Trustee.

     All payments made on the Series 1999A (Burke) Note shall be made to the
Series 1999A (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.

     SECTION 1.2 FORM OF THE SERIES 1999A (BURKE) NOTE.

     The Series 1999A (Burke) Note, including the Trustee's authentication
certificate to be executed on such Series 1999A (Burke) Note shall be
substantially in the form of EXHIBIT B attached hereto, with such appropriate
insertions, omissions, substitutions and other variations as are required or
permitted in the Original Indenture.

     SECTION 1.3 SUBSTITUTION OF THE SERIES 1999A (BURKE) NOTE FOR THE UNSECURED
NOTE.

     Upon its authentication, the Series 1999A (Burke) Note shall be delivered
to the Series 1999A (Burke) Trustee in substitution for the Unsecured Note in
accordance with Section 4.9 of the Series 1999A (Burke) Loan Agreement.
Thereafter, the Series 1999A (Burke) Note shall evidence the loan theretofore
evidenced by the Unsecured Note.

                                       6
<PAGE>

                                   ARTICLE II

                                  MISCELLANEOUS

     SECTION 2.1 This Eleventh Supplemental Indenture is executed and shall be
construed as an indenture supplemental to the Original Indenture, and shall form
a part thereof, and the Original Indenture, as heretofore supplemented and as
hereby supplemented and modified, is hereby confirmed. Except to the extent
inconsistent with the express terms hereof, all of the provisions, terms,
covenants and conditions of the Indenture shall be applicable to the Series
1999A (Burke) Note to the same extent as if specifically set forth herein. All
references herein to Sections, definitions or other provisions of the Original
Indenture shall be to such Sections, definitions and other provisions as they
may be amended or modified from time to time pursuant to the Indenture. All
capitalized terms used in this Eleventh Supplemental Indenture shall have the
same meanings ascribed to them in the Original Indenture, except in cases where
the context clearly indicates otherwise.

     SECTION 2.2 All recitals in this Eleventh Supplemental Indenture are made
by the Company only and not by the Trustee; and all of the provisions contained
in the Original Indenture, in respect of the rights, privileges, immunities,
powers and duties of the Trustee shall be applicable in respect hereof as fully
and with like effect as if set forth herein in full.

     SECTION 2.3 Whenever in this Eleventh Supplemental Indenture any of the
parties hereto is named or referred to, this shall, subject to the provisions of
Articles IX and XI of the Original Indenture, be deemed to include the
successors and assigns of such party, and all the covenants and agreements in
this Eleventh Supplemental Indenture contained by or on behalf of the Company,
or by or on behalf of the Trustee shall, subject as aforesaid, bind and inure to
the respective benefits of the respective successors and assigns of such
parties, whether so expressed or not.

     SECTION 2.4 Nothing in this Eleventh Supplemental Indenture, expressed or
implied, is intended, or shall be construed, to confer upon, or to give to, any
person, firm or corporation, other than the parties hereto and the Holders of
the Outstanding Secured Obligations, any right, remedy or claim under or by
reason of this Eleventh Supplemental Indenture or any covenant, condition,
stipulation, promise or agreement hereof, and all the covenants, conditions,
stipulations, promises and agreements in this Eleventh Supplemental Indenture
contained by or on behalf of the Company shall be for the sole and exclusive
benefit of the parties hereto, and of the Holders of Outstanding Secured
Obligations.

     SECTION 2.5 This Eleventh Supplemental Indenture may be executed in several
counterparts, each of such counterparts shall for all purposes be deemed to be
an original, and all such counterparts, or as many of them as the Company and
the Trustee shall preserve undestroyed, shall together constitute but one and
the same instrument.

                                       7
<PAGE>

     SECTION 2.6 To the extent permitted by applicable law, this Eleventh
Supplemental Indenture shall be deemed to be a Security Agreement and Financing
Statement whereby the Company grants to the Trustee a security interest in all
of the Trust Estate that is personal property or fixtures under the Uniform
Commercial Code, as adopted or hereafter adopted in one or more of the states in
which any part of the properties of the Company are situated. The mailing
address of the Company,

as debtor is:                       2100 East Exchange Place
                                    P. O. Box 1349
                                    Tucker, Georgia 30085-1349,

and the mailing address of the Trustee, as secured party, is:

                                    SunTrust Bank
                                    25 Park Place
                                    Atlanta, Georgia 30303-2900

                           [Signatures on Next Page.]

                                       8
<PAGE>

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

COMPANY:                            OGLETHORPE POWER
                                    CORPORATION (AN ELECTRIC MEMBERSHIP
                                    CORPORATION), an electric membership
                                    corporation organized under the laws
                                    of the State of Georgia

2100 East Exchange Place
P. O. Box 1349
Tucker, Georgia 30085-1349

                                    By: /S/ THOMAS A. SMITH
                                    ----------------------------
                                        Thomas A. Smith
                                        President and Chief Executive Officer

Signed, sealed and delivered        Attest: /S/ PATRICIA N. NASH
by the Company in the presence of:  ----------------------------
                                        Patricia N. Nash
                                        Secretary

 /S/ LYNN H. LESTER
---------------------------
Witness

 /S/ THOMAS J. BRENDIAR
---------------------------
Notary Public                        [CORPORATE SEAL]

(Notarial Seal)

My commission expires:   NOVEMBER 14, 2000
                      --------------------------------

                      [Signatures Continued on Next Page.]

<PAGE>

                   [Signatures Continued from Previous Page.]

TRUSTEE:                        SUNTRUST BANK,
                                a banking corporation organized and existing
                                under the laws of the State of Georgia

                                By: /S/ BARTON A. DONALDSON
                                    -----------------------
Signed, sealed and delivered        Barton A. Donaldson
by the Trustee in the               Vice President
presence of:

                                By: /S/ BRIAN E. WOMBLE
                                ---------------------------------------------
 /S/ GEORGE T. HOGAN                Brian E. Womble
--------------------                Assistant Vice President
Witness

 /S/ TERESA R. TURNER
---------------------
Notary Public                      [BANK SEAL]

(Notarial Seal)

My commission expires:      APRIL 3, 2001
                      ----------------------------

<PAGE>

                               EXHIBIT A

     All property of the Company in the Counties of Appling, Ben Hill, Burke,
Carroll, Clarke, Cobb, DeKalb, Floyd, Fulton, Heard, Jackson, Monroe, and
Toombs, State of Georgia, including, without limitation, the properties more
specifically described below:

    No additional properties to be specifically described.

                                      A-1
<PAGE>

                                    EXHIBIT B

                       [Form of Series 1999A (Burke) Note]

THIS NOTE IS NON-TRANSFERABLE EXCEPT AS MAY BE REQUIRED TO EFFECT ANY TRANSFER
TO ANY SUCCESSOR TRUSTEE UNDER THE TRUST INDENTURE, DATED AS OF NOVEMBER 1,
1999, BETWEEN THE DEVELOPMENT AUTHORITY OF BURKE COUNTY AND SUNTRUST BANK,
ATLANTA, AS TRUSTEE.

                          OGLETHORPE POWER CORPORATION
                      (AN ELECTRIC MEMBERSHIP CORPORATION)

                           SERIES 1999A (BURKE) NOTE      DATE: January __, 2000

                                (VOGTLE PROJECT)

         OGLETHORPE POWER CORPORATION (AN ELECTRIC MEMBERSHIP CORPORATION)
("Oglethorpe"), an electric membership corporation organized and existing
under the laws of the State of Georgia, for value received and in
consideration of the agreement of the Development Authority of Burke County
(the "Burke Authority") to issue $14,145,000 in aggregate principal amount of
Development Authority of Burke County Pollution Control Revenue Bonds
(Oglethorpe Power Corporation Vogtle Project), Series 1999A (the "Series
1999A (Burke) Bonds"), hereby promises to pay to SunTrust Bank, formerly
known as SunTrust Bank, Atlanta (the "Series 1999A (Burke) Trustee"), as
assignee and pledgee of the Burke Authority, acting pursuant to the Trust
Indenture, dated as of November 1, 1999, from the Burke Authority to the
Series 1999A (Burke) Trustee (the "Series 1999A Indenture"), or its successor
in trust, the principal sum of $14,145,000, together with interest and
prepayment premium (if any) thereon as follows:

     (a) on or before each Interest Payment Date (as defined in the Series 1999A
Indenture), a sum which will equal the interest on the Series 1999A (Burke)
Bonds which will become due on such Interest Payment Date on the Series 1999A
(Burke) Bonds; and

     (b) on or before January 1, 2020, a sum which will equal the principal
amount of the Series 1999A (Burke) Bonds which will become due on January 1,
2020; and

     (c) on or before any redemption date for the Series 1999A (Burke) Bonds, a
sum equal to the principal of, redemption premium (if any) and interest on, the
Series 1999A (Burke) Bonds which are to be redeemed on such date.

                                      B-1
<PAGE>

     This Series 1999A (Burke) Note is issued in substitution for and supersedes
and replaces that certain Series 1999A (Burke) Note, dated November 17, 1999, by
Oglethorpe to the Series 1999A (Burke) Trustee which was executed and delivered
contemporaneously with the initial issuance of the Series 1999A (Burke) Bonds.
This Series 1999A (Burke) Note evidences the Loan (as defined in the Agreement
hereinafter referred to) of the Burke Authority to Oglethorpe and the obligation
to repay the same and shall be governed by and shall be payable in accordance
with the terms, conditions and provisions of the Loan Agreement, dated November
1, 1999 (the "Agreement"), between the Burke Authority and Oglethorpe, pursuant
to which the Burke Authority has agreed to loan to Oglethorpe the proceeds from
the sale of the Series 1999A (Burke) Bonds.

     This Series 1999A (Burke) Note is a duly authorized obligation of
Oglethorpe issued under and equally and ratably secured by the Indenture, dated
as of March 1, 1997 (the "Original Indenture"), as heretofore supplemented and
as supplemented by the Eleventh Supplemental Indenture, dated as of January 1,
2000 (the "Eleventh Supplemental Indenture"), and the Twelfth Supplemental
Indenture, dated as of January 1, 2000 (the "Twelfth Supplemental Indenture"),
between Oglethorpe, as grantor, and SunTrust Bank, formerly known as SunTrust
Bank, Atlanta, as trustee (in such capacity, the "Indenture Trustee"), (the
Original Indenture, as supplemented, the " Indenture"). Reference is hereby made
to the Indenture for a statement of the description of the properties thereby
mortgaged, pledged and assigned, the nature and extent of the security and the
respective rights, limitations of rights, duties and immunities thereunder of
Oglethorpe, the Indenture Trustee and the holder of this Series 1999A (Burke)
Note and of the terms upon which this Series 1999A (Burke) Note is authenticated
and delivered. This Series 1999A (Burke) Note is created by the Eleventh
Supplemental Indenture and designated as the "Series 1999A (Burke) Note."

     All payments hereon are to be made to the Series 1999A (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 day payment is due. As set
forth in Section 4.6 of the Agreement, the obligation of Oglethorpe to make the
payments required hereunder shall be absolute and unconditional.

     Oglethorpe shall be entitled to certain credits against payments required
to be made hereunder as provided in Section 4.3 of the Agreement.

     This Series 1999A (Burke) Note may be prepaid upon the terms and conditions
set forth in Article VIII of the Agreement.

     If the Series 1999A (Burke) Trustee shall accelerate payment of the Series
1999A (Burke) Bonds, all payments on this Series 1999A (Burke) Note shall be
declared due and payable in the manner and with the effect provided in the
Agreement. The Agreement provides that, under certain conditions, such
declaration shall be rescinded by the Series 1999A (Burke) Trustee.

     No recourse shall be had for the payments required hereby or for any claim
based herein or in the Agreement or in the Indenture against any officer,
director or member, past, present or future,

                                      B-2
<PAGE>

of Oglethorpe as such, either directly or through Oglethorpe, or under any
constitution provision, statute or rule of law or by the enforcement of any
assessment or by any legal or equitable proceedings or otherwise.

     This Series 1999A (Burke) Note shall not be entitled to any benefit under
the Indenture and shall not become valid or obligatory for any purposes until
the Indenture Trustee shall have signed the form of authentication certificate
endorsed hereon.

     This Series 1999A (Burke) Note shall be governed by and construed in
accordance with the laws of the State of Georgia.

                                      B-3
<PAGE>

     IN WITNESS WHEREOF, Oglethorpe has caused this Series 1999A (Burke) Note to
be executed in its corporate name by its President and Chief Executive Officer
and attested by its Secretary and its corporate seal to be hereunto affixed.

                                  OGLETHORPE POWER CORPORATION
                                  (AN ELECTRIC MEMBERSHIP
                                  CORPORATION)

                                  By:
                                     ----------------------------------
                                     Thomas A. Smith
                                     President and Chief Executive Officer

(SEAL)

Attest:

-------------------------------
Patricia N. Nash
Secretary

                                      B-4
<PAGE>

                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION

     This is one of the Obligations of the series designated therein referred to
in the within mentioned Indenture.

                                      SUNTRUST BANK, as Trustee

                                      By:
                                        ----------------------------------
                                         Authorized Signatory

                                      B-5

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