Exhibit 10.1

FIFTEENTH SUPPLEMENTAL INDENTURE

THIS FIFTEENTH SUPPLEMENTAL INDENTURE, dated as of April 3, 2006 (the “Fifteenth
Supplemental Indenture”), among Duke Energy Corporation, a North Carolina
corporation (“Duke Energy”), Duke Energy Holding Corp., a Delaware corporation
(formerly named Deer Holding Corp.) (“Duke Holdco”) and JPMorgan Chase Bank,
N.A. (formerly known as The Chase Manhattan Bank), a national banking
association, as trustee under the Indenture referred to below (the “Trustee”).

W I T N E S S E T H

WHEREAS, Duke Energy has heretofore entered into the Senior Indenture, dated as
of September 1, 1998 (the “Original Indenture”), with the Trustee, as
supplemented to the date hereof (as so supplemented, the “Indenture”);

WHEREAS, Duke Energy currently has issued and Outstanding the notes of the
series listed on Schedule A hereto (collectively, the “Notes”) under the
Indenture;

WHEREAS, on May 3, 2005, Duke Energy incorporated Duke Holdco as a direct,
wholly-owned subsidiary of Duke Energy, and Duke Holdco incorporated Deer
Acquisition Corp., a North Carolina corporation (“Merger Sub A”), and Cougar
Acquisition Corp., a Delaware corporation (“Merger Sub B”), each as a direct,
wholly-owned subsidiary of Duke Holdco;

WHEREAS, Duke Energy entered into the Agreement and Plan of Merger, dated as of
May 8, 2005, as amended (the “Merger Agreement”), by and among Duke Energy,
Cinergy Corp., a Delaware corporation (“Cinergy”), Duke Holdco, Merger Sub A and
Merger Sub B, providing for the consummation of the business combination
contemplated therein;

WHEREAS, pursuant to the terms of the Merger Agreement, Merger Sub A shall merge
with and into Duke Energy (the “Duke Energy Merger”), in accordance with the
North Carolina Business Corporation Act (“NCBCA”), whereby Duke Energy shall be
the surviving corporation in the Duke Energy Merger and shall continue its
existence under the laws of the State of North Carolina and shall succeed to and
assume all the rights and obligations of Merger Sub A in accordance with the
NCBCA and, as a result of the Duke Energy Merger, shall be a direct,
wholly-owned subsidiary of Duke Holdco;

WHEREAS, following effectiveness of the Duke Energy Merger, Duke Energy shall
convert its form of organization into a limited liability company pursuant to a
plan of conversion adopted pursuant to Section 55-11A-11 of the NCBCA and
Section 57C-9A-02 of the North Carolina Limited Liability Company Act and shall
be renamed Duke Power Company LLC, all of whose membership or other equity
interests shall be held by Duke Holdco (the “Duke Energy Conversion” and,
together with the Duke Energy Merger, the “Duke Energy Reorganization”);

WHEREAS, Duke Energy is currently the direct owner of 100% of the issued and
outstanding equity interests of Duke Capital LLC, a Delaware limited liability
company (“Duke Capital”);

WHEREAS, following effectiveness of the Duke Energy Reorganization, Duke Energy
shall distribute to Duke Holdco all the issued and outstanding equity interests
of Duke Capital (the “Duke Capital Distribution”) and, as a result, each of Duke
Energy and Duke Capital shall be a direct, wholly-owned subsidiary of Duke
Holdco;

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WHEREAS, in connection with the Duke Capital Distribution, Duke Holdco desires
to fully and unconditionally guarantee the payment obligations of Duke Energy
with respect to the Notes as long as the Notes remain Outstanding;

WHEREAS, Section 901(9) of the Original Indenture provides, among other things,
that Duke Energy, when authorized by a Board Resolution, and the Trustee, at any
time and from time to time, may enter into an indenture supplemental to the
Original Indenture for the purpose of making any provisions with respect to
matters arising under the Indenture, provided that such action does not
adversely affect the interests of the Holders of Securities of any series in any
material respect;

WHEREAS, the execution of the Fifteenth Supplemental Indenture is authorized and
permitted by Section 901 of the Original Indenture and all conditions precedent
provided for in the Indenture relating to the execution of the Fifteenth
Supplemental Indenture have been complied with; and

WHEREAS, this Fifteenth Supplemental Indenture is being executed prior to the
closing of the transactions contemplated by the Merger Agreement, including the
Duke Energy Merger and the Duke Energy Reorganization, and shall be effective
simultaneously with the Duke Capital Distribution.

NOW, THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, Duke
Energy, Duke Holdco and the Trustee mutually covenant and agree for the equal
and ratable benefit of the Holders from time to time of the Notes (the
“Holders”) as follows:

SECTION 101. Capitalized Terms. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Original Indenture.

SECTION 102. Guarantee. Duke Holdco does hereby fully and unconditionally
guarantee for the benefit of the Holders and the Trustee (the “Guarantee”)
(a) the due and punctual payment of the principal of, premium, if any, and
interest on, all the Notes, whether at Stated Maturity, by declaration of
acceleration, call for redemption or otherwise, the due and punctual payment of
interest on overdue principal of, premium, if any, and interest on all the
Notes, if any, if lawful, and the due and punctual performance of all other
obligations of Duke Energy to the Holders or the Trustee in accordance with the
terms of the Indenture, and (b) in case of any extension of time of payment or
renewal of any Notes or any such other obligations, that the same will be
promptly paid in full when due or performed in accordance with the terms of the
extension or renewal, whether at stated maturity, by acceleration or otherwise.

In case of the failure of Duke Energy to punctually make any such principal,
premium, if any, or interest payment, Duke Holdco hereby agrees to cause any
such payment to be made promptly when and as the same shall become due and
payable, whether at Stated Maturity, by declaration of acceleration, call for
redemption or otherwise, and as if such payment were made by Duke Energy.

Duke Holdco hereby agrees that its obligations under the Guarantee shall be as
if it were principal debtor and not merely surety, and shall be absolute and
unconditional, irrespective of, and shall be unaffected by, any invalidity,
irregularity or unenforceability of any Note of any series or the Indenture, any
failure to enforce the provisions of any Note of any series or this Indenture,
or any waiver, modification or indulgence granted to Duke Energy with respect
thereto, by the Holder of any Note of any series or the Trustee, or any other
circumstance which may otherwise constitute a legal or equitable discharge of a
surety or guarantor; provided, however, that, notwithstanding the foregoing, no
such waiver, modification or indulgence shall, without the consent of Duke
Holdco, increase the principal amount of a Note or the interest rate thereon or
increase any premium payable upon redemption thereof. Duke Holdco hereby waives
diligence, presentment, demand of payment, filing of claims with a court in

 

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the event of a merger or bankruptcy of Duke Energy, any right to require a
proceeding first against Duke Energy, protest or notice with respect to any Note
or the indebtedness evidenced thereby or with respect to any sinking fund
payment required pursuant to the terms of a Note issued under the Indenture and
all demands whatsoever, and covenants that the Guarantee will not be discharged
with respect to any Note except by payment in full of the principal of (and
premium, if any) and interest on such Note. The Guarantee shall constitute a
guarantee of payment and not of collection and shall not be impaired by the
failure to endorse evidence of the Guarantee on any Note.

Duke Holdco shall be subrogated to all rights of the Holder of a Note against
Duke Energy in respect of any amounts paid to such Holder by Duke Holdco
pursuant to the provisions of the Guarantee; provided, however, that Duke Holdco
shall not be entitled to enforce, or to receive any payments arising out of or
based upon, such right of subrogation until the principal of (and premium, if
any) and interest on all Notes of the relevant series shall have been paid in
full.

SECTION 103. Limitation on Liens. Duke Holdco will not, while any of the Notes
remains Outstanding, create or suffer to be created or to exist, any mortgage,
lien, pledge, security interest or other encumbrance of any kind upon any
property of Duke Holdco, whether now owned or hereafter acquired, to secure any
indebtedness for borrowed money of Duke Holdco, unless it shall make effective
provisions whereby the Notes then Outstanding shall be secured by such mortgage,
lien, pledge, security interest or other encumbrance equally and ratably with
any and all indebtedness for borrowed money thereby secured so long as any such
indebtedness shall be so secured; provided, however, that nothing in this
Section shall be construed to prevent Duke Holdco from creating, or from
suffering to be created or to exist, any mortgages, liens, pledges, security
interests or other encumbrances, or any agreements, with respect to:

(1) purchase money mortgages, or other purchase money liens, pledges, security
interests or encumbrances of any kind upon property hereafter acquired by Duke
Holdco, or mortgages, liens, pledges, security interests or other encumbrances
of any kind existing on any property at the time of the acquisition thereof
(including mortgages, liens, pledges, security interests or other encumbrances
which exist on any property of a Person which is consolidated with or merged
with or into Duke Holdco or which transfers or leases all or substantially all
of its properties to Duke Holdco), or conditional sales agreements or other
title retention agreements and leases in the nature of title retention
agreements with respect to any property hereafter acquired; provided, however,
that no such mortgage, lien, pledge, security interest or other encumbrance
shall extend to or cover any other property of Duke Holdco;

(2) mortgages, liens, pledges, security interests or other encumbrances of any
kind upon any property of Duke Holdco existing as of the date of the Fifteenth
Supplemental Indenture; liens for taxes or assessments or other governmental
charges or levies; pledges or deposits to secure obligations under worker’s
compensation laws, unemployment insurance and other social security legislation,
including liens of judgments thereunder which are not currently dischargeable;
pledges or deposits to secure performance in connection with bids, tenders,
contracts (other than contracts for the payment of money) or leases to which
Duke Holdco is a party; pledges or deposits to secure public or statutory
obligations of Duke Holdco; builders’, materialmen’s, mechanics’, carriers’,
warehousemen’s, workers’, repairmen’s, operators’, landlords’ or other like
liens in the ordinary course of business, or deposits to obtain the release of
such liens; pledges or deposits to secure, or in lieu of, surety, stay, appeal,
indemnity, customs, performance or return-of-money bonds; other pledges or
deposits for similar purposes in the ordinary course of business; liens created
by or resulting from any litigation or proceeding which at the time is being
contested in good faith by appropriate proceedings; liens incurred in connection
with the issuance of bankers’ acceptances and lines of credit, bankers’ liens or
rights of offset and any security given in the ordinary course of business to
banks or others to secure any indebtedness payable on demand or maturing within
12 months of the date that such indebtedness is originally incurred; liens
incurred in connection with repurchase, swap or other similar agreements
(including, without limitation, commodity price,

 

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currency exchange and interest rate protection agreements); leases made, or
existing on property acquired, in the ordinary course of business; liens
securing industrial revenue or pollution control bonds; liens, pledges, security
interests or other encumbrances on any property arising in connection with any
defeasance, covenant defeasance or in-substance defeasance of indebtedness of
Duke Holdco, including its guarantee obligations in respect of the Notes; liens
created in connection with, and created to secure, a non-recourse obligation;
zoning restrictions, easements, licenses, rights-of-way, restrictions on the use
of property or minor irregularities in title thereto, which do not, in the
opinion of Duke Holdco, materially impair the use of such property in the
operation of the business of Duke Holdco or the value of such property for the
purpose of such business;

(3) First and Refunding Mortgage Bonds of the Corporation issued or to be issued
from time to time under the First and Refunding Mortgage dated as of December 1,
1927 from the Corporation to the trustee named therein, as supplemented and
amended and as to be supplemented and amended;

(4) indebtedness which may be issued by Duke Holdco in connection with a
consolidation or merger of Duke Holdco with or into any other Person (which may
be an Affiliate of Duke Holdco) in exchange for or otherwise in substitution for
secured indebtedness of such Persons (“Third Party Debt”) which by its terms
(i) is secured by a mortgage on all or a portion of the property of such Person,
(ii) prohibits secured indebtedness from being incurred by such Person, unless
the Third Party Debt shall be secured equally and ratably with such secured
indebtedness or (iii) prohibits secured indebtedness from being incurred by such
Person;

(5) indebtedness of any Person which is required to be assumed by Duke Holdco in
connection with a consolidation or merger of such Person, with respect to which
any property of Duke Holdco is subjected to a mortgage, lien, pledge, security
interest or other encumbrance;

(6) mortgages, liens, pledges, security interests or other encumbrances of any
kind upon any property acquired, constructed, developed, or improved by Duke
Holdco (whether alone or in association with others) after the date of this
Fifteenth Supplemental Indenture which are created prior to, at the time of, or
within 18 months after such acquisition (or in the case of property constructed,
developed or improved, after the completion of such construction, development or
improvement and commencement of full commercial operation of such property,
whichever is later) to secure or provide for the payment of any part of the
purchase price or cost thereof; provided that in the case of such construction,
development or improvement the mortgages, liens, pledges, security interests or
other encumbrances shall not apply to any property theretofore owned by Duke
Holdco other than theretofore unimproved real property;

(7) Mortgages, liens, pledges, security interests or other encumbrances
permitted to be incurred by Duke Energy and Cinergy and their respective
subsidiaries pursuant to their respective debt instruments outstanding on the
date hereof;

(8) the replacement, extension or renewal (or successive replacements,
extensions or renewals), as a whole or in part, of any mortgage, lien, pledge,
security interest or other encumbrance, or of any agreement, referred to above
in clauses (1) through (7) inclusive, or the replacement, extension or renewal
(not exceeding the principal amount of indebtedness secured thereby together
with any premium, interest, fee or expense payable in connection with any such
replacement, extension or renewal) of the indebtedness secured thereby; provided
that such replacement, extension or renewal is limited to all or a part of the
same property that secured the mortgage, lien, pledge, security interest or
other encumbrance replaced, extended or renewed (plus improvements thereon or
additions or accessions thereto); or

(9) any other mortgage, lien, pledge, security interest or other encumbrance not
excepted by the foregoing clauses (1) through (8); provided that immediately
after the creation or assumption of such mortgage, lien, pledge, security
interest or other encumbrance, the aggregate principal amount of indebtedness
for borrowed money of Duke Holdco secured by all mortgages, liens, pledges,
security

 

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interests and other encumbrances created or assumed under the provisions of this
clause (9) shall not exceed an amount equal to 10% of common stockholders’
equity of Duke Holdco as shown on its consolidated balance sheet for the
accounting period occurring immediately prior to the creation or assumption of
such mortgage, lien, pledge, security interest or other encumbrance.

This Section 103 shall be for the sole benefit of the Notes and not for the
benefit of any future series of Securities Outstanding under the Indenture
unless Duke Holdco agrees otherwise.

SECTION 104. Duke Holdco May Consolidate, Etc., on Certain Terms. (1) Nothing
contained in the Indenture, this Fifteenth Supplemental Indenture or in any of
the Notes shall prevent any consolidation or merger of Duke Holdco with or into
any other Person or Persons (whether or not affiliated with Duke Holdco), or
successive consolidations or mergers in which Duke Holdco or its successor or
successors shall be a party or parties, or shall prevent any conveyance or
transfer of the properties and assets of Duke Holdco as an entirety or
substantially as an entirety to any other Person (whether or not affiliated with
Duke Holdco) lawfully entitled to acquire the same; provided, however, and Duke
Holdco hereby covenants and agrees, that upon any such consolidation, merger,
conveyance or transfer, (i) the obligations of Duke Holdco as set forth in
Section 102 herein shall be expressly assumed, by a supplemental indenture, in
form reasonably satisfactory to the Trustee, executed and delivered to the
Trustee by the Person (if other than Duke Holdco) formed by such consolidation,
or into which Duke Holdco shall have been merged, or by the Person which shall
have acquired such properties and assets and (ii) Duke Holdco shall deliver to
the Trustee an Officers’ Certificate and an Opinion of Counsel, each stating
that such consolidation, merger, conveyance or transfer and, if a supplemental
indenture is required in connection with such transaction, such supplemental
indenture, comply with this Section and that all conditions precedent herein
provided for relating to such transaction have been complied with.

Solely for the purpose of clause (ii) of this Section 104(1), the term
“Corporation,” appearing in the definition of the term “Officers’ Certificate”
in Section 101 of the Original Indenture, shall be changed to “Duke Holdco.”

(2) Upon any consolidation of Duke Holdco with, or merger of Duke Holdco into,
any other Person or any conveyance or transfer of the properties and assets of
Duke Holdco as an entirety or substantially as an entirety in accordance with
this Section, the successor Person formed by such consolidation or into which
Duke Holdco is merged or to which such conveyance or transfer is made shall
succeed to, and be substituted for, and may exercise every right and power of,
Duke Holdco under this Fifteenth Supplemental Indenture and the Indenture with
the same effect as if such successor Person had been named as Duke Holdco
herein, and thereafter the predecessor Person shall be relieved of all
obligations and covenants under this Fifteenth Supplemental Indenture, the
Indenture and the Notes.

This Section 104 shall be for the sole benefit of the Notes and not for the
benefit of any future series of Securities Outstanding under the Indenture
unless Duke Holdco agrees otherwise.

SECTION 105. Miscellaneous Amendments.

(1) Section 102 of the Original Indenture is hereby amended by adding the
following definition:

“Duke Holdco” means Duke Energy Holding Corp., a Delaware corporation (formerly
named Deer Holding Corp.).

(2) Section 105 of the Original Indenture is hereby amended by deleting “or”
after clause (1) thereof, by deleting the period after clause (2) thereof and
inserting “, or” in its place and by adding the following clause (3):

 

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“(3) Duke Holdco by the Trustee or by any Holder shall be sufficient for every
purpose hereunder (unless otherwise herein expressly provided) if in writing and
mailed, first-class postage prepaid, to Duke Holdco addressed to it at 526 South
Church Street, Charlotte, North Carolina 28202, Attention: Treasurer, or at any
other address previously furnished in writing to the Trustee by Duke Holdco.”;

(3) Section 501(4) of the Original Indenture is hereby amended to read as
follows:

“(4) default in the performance, or breach, of any covenant of the Corporation
or Duke Holdco in this Indenture (other than a covenant a default in whose
performance or whose breach is elsewhere in this Section specifically dealt with
or which has expressly been included in this Indenture solely for the benefit of
series of Securities other than that series), and continuance of such default or
breach for a period of 90 days after there has been given, by registered or
certified mail, to the Corporation or Duke Holdco, as the case may be, by the
Trustee or to the Corporation or Duke Holdco, as the case may be, and the
Trustee by the Holders of at least 33% in principal amount of the Outstanding
Securities of that series a written notice specifying such default or breach and
requiring it to be remedied and stating that such notice is a “Notice of
Default” hereunder, unless the Trustee, or the Trustee and the Holders of a
principal amount of Securities of such series not less than the principal amount
of Securities the Holders of which gave such notice, as the case may be, shall
agree in writing to an extension of such period prior to its expiration;
provided, however, that the Trustee, or the Trustee and the Holders of such
principal amount of Securities of such series, as the case may be, shall be
deemed to have agreed to an extension of such period if corrective action is
initiated by the Corporation or Duke Holdco, as the case may be, within such
period and is being diligently pursued; or” and

(4) Section 704 of the Original Indenture is hereby amended to read as follows:

The Corporation, or Duke Holdco (if the Corporation’s obligation to file
separate reports to the Commission pursuant to the Trust Indenture Act or
Section 13 or Section 15(d) of the Exchange Act shall be terminated or expressly
assumed by Duke Holdco), shall file with the Trustee and the Commission, and
transmit to Holders, such information, documents and other reports, and such
summaries thereof, as may be required pursuant to the Trust Indenture Act at the
times and in the manner provided pursuant to such Act; provided that any such
information, documents or reports required to be filed with the Commission
pursuant to Section 13 or Section 15(d) of the Exchange Act shall be filed with
the Trustee within 15 days after the same is so required to be filed with the
Commission.

(5) Section 901(1) of the Original Indenture is hereby amended to read as
follows:

“(1) to evidence the succession of another person to the Corporation or Duke
Holdco, as the case may be, and the assumption by any such successor of the
covenants of, respectively, the Corporation or Duke Holdco herein and in the
Securities; or”.

This Section 105 shall be for the sole benefit of the Notes and not for the
benefit of any future series of Securities Outstanding under the Indenture
unless Duke Holdco agrees otherwise.

SECTION 106. No Recourse Against Others. No past, present or future director,
officer, employee, incorporator, stockholder, partner or agent of Duke Holdco
shall have any liability for any obligations of Duke Energy or Duke Holdco under
the Notes, the Guarantee, the Indenture or the Fifteenth Supplemental Indenture
or for any claim based on, in respect of, or by reason of, such obligations or
their creation.

 

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SECTION 107. Provisions Binding on Successors. All the covenants, stipulations,
premises and agreements made in the Fifteenth Supplemental Indenture by Duke
Energy and Duke Holdco shall bind their respective successors and assigns
whether so expressed or not.

SECTION 108. New York Contract. THIS FIFTEENTH SUPPLEMENTAL INDENTURE AND THE
GUARANTEE SHALL BE DEEMED TO BE A CONTRACT MADE UNDER THE LAWS OF THE STATE OF
NEW YORK AND FOR ALL PURPOSES SHALL BE CONSTRUED IN ACCORDANCE WITH THE LAWS OF
SAID STATE.

SECTION 109. Execution and Counterparts. The Fifteenth Supplemental Indenture
may be executed in any number of counterparts, each of which when so executed
shall be deemed to be an original, but all such counterparts shall together
constitute but one and the same instrument.

SECTION 110. Effect of Headings. The Section headings herein are for convenience
only and shall not affect the construction hereof.

SECTION 111. The Trustee. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of the Fifteenth
Supplemental Indenture or for or in respect of the recitals contained herein,
all of which recitals are made solely by Duke Energy and Duke Holdco.

SECTION 112. Full Force and Effect. Except as expressly amended hereby, the
Indenture shall remain in full force and effect in accordance with the
provisions thereof on the date thereof.

SECTION 113. Effectiveness of the Fifteenth Supplemental Indenture. The
Fifteenth Supplemental Indenture shall be effective simultaneously with the Duke
Capital Distribution. Promptly following the occurrence of the Duke Capital
Distribution, Duke Energy shall provide notice thereof to the Trustee.

 

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IN WITNESS WHEREOF, the parties hereto have caused the Fifteenth Supplemental
Indenture to be duly executed, all as of the date first above written.

 

DUKE ENERGY CORPORATION By:  

 

Name:   David L. Hauser Title:   Group Vice President and   Chief Financial
Officer

 

Attest:

 

Name:

Title:

 

DUKE ENERGY HOLDING CORP. By:              

 

Name:   Robert T. Lucas III Title:   Assistant Secretary

 

Attest:

 

Name:

Title:

 

JPMORGAN CHASE BANK, N.A., as Trustee

By:

 

 

Name:

 

Title:

 

 

Attest:

 

Name:

Title:

 

Supplemental Indenture

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SCHEDULE A

Outstanding Notes

 

  •   $300,000,000 Series A 6% Senior Notes due 2028

 

  •   $200,000,000 Series B 5 3/8% Senior Notes due 2009

 

  •   $300,000,000 Series D 7 3/8% Senior Notes due 2010

 

  •   $750,000,000 6.25% Senior Notes due 2012

 

  •   $250,000,000 6.60% Insured Quarterly Senior Notes due 2022

 

  •   $350,000,000 6.45% Senior Notes due 2032

 

  •   $110,000,000 4.611% Senior Notes due 2007

 

  •   $400,000,000 5.625% Senior Notes due 2012

 

  •   $742,000,000 1 3/4% Convertible Senior Notes due 2023

 

  •   $300,000,000 4.20% Senior Notes due 2008