FIFTY-SEVENTH SUPPLEMENTAL INDENTURE TO INDENTURE

Exhibit 4.1

FIFTY-SEVENTH SUPPLEMENTAL
INDENTURE

TO

INDENTURE DATED SEPTEMBER 1, 1939

DUKE ENERGY INDIANA, INC .
(FORMERLY NAMED EACH OF “PSI ENERGY, INC.” AND “PUBLIC SERVICE COMPANY OF INDIANA, INC.” AND
SUCCESSOR BY CONSOLIDATION TO PUBLIC SERVICE COMPANY OF INDIANA)

TO

LASALLE BANK NATIONAL ASSOCIATION
AS TRUSTEE
( FORMERLY NAMED “LASALLE NATIONAL BANK” AND THE
SUCCESSOR TRUSTEE TO THE FIRST NATIONAL BANK OF CHICAGO)

DATED AS OF AUGUST 21, 2008

CREATING FIRST MORTGAGE BONDS, SERIES LLL, 6.35%, DUE AUGUST 15, 2038

AND

OTHERWISE SUPPLEMENTING AND AMENDING THE INDENTURE

TABLE OF CONTENTS

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      Fifty-Seventh Supplemental Indenture dated as of the twenty-first day of August, 2008, made and entered into by and between Duke Energy Indiana, Inc. (hereinafter commonly referred to as the “Company”), a corporation organized and existing under the laws of the State of Indiana, formerly named each of PSI Energy, Inc. and Public Service Company of Indiana, Inc., and the successor by consolidation to Public Service Company of Indiana, an Indiana corporation, party of the first part, and LaSalle Bank National Association , a national banking association organized and existing under the laws of the United States and having its office or place of business in the City of Chicago, State of Illinois, formerly named LaSalle National Bank, and the successor trustee to The First National Bank of Chicago (hereinafter commonly referred to as the “Trustee”), party of the second part,

      Witnesseth:

      Whereas , Public Service Company of Indiana (hereinafter commonly referred to as the “Initial Mortgagor”), prior to its consolidation with certain other corporations to form the Company, executed and delivered to the Trustee a certain indenture of mortgage or deed of trust (hereinafter called the “original Indenture” when referred to as existing prior to any amendment thereto, and the “Indenture” when referred to as heretofore, now or hereafter amended), dated September 1, 1939, and a First Supplemental Indenture thereto, dated as of March 1, 1941, to secure the bonds of the Initial Mortgagor, its successors and assigns, issued from time to time under the Indenture in series for the purposes of and subject to the limitations specified in the Indenture; and

      Whereas , the Company on September 6, 1941, became, through a consolidation, the successor of the Initial Mortgagor (and four other companies) and succeeded to all the rights and became liable for all the obligations of the Initial Mortgagor (and such other companies); and

      Whereas , after said consolidation, the Company executed and delivered a Second Supplemental Indenture, dated as of November 1, 1941, to the original Indenture for the purposes, among others, of (i) the making by the Company of an agreement of assumption and adoption by it of the Indenture, (ii) the assumption by the Company of the bonds (and interest and premium, if any, thereon) issued or to be issued under the Indenture, and of all terms, covenants and conditions binding upon it under the Indenture, and the agreeing by the Company to pay, perform and fulfill the same, and (iii) the conveying to the Trustee upon the trusts declared in the Indenture, but subject to any outstanding liens and encumbrances, all the property which the Company then owned or which it might thereafter acquire, except property of a character similar to the property of the Initial Mortgagor which is excluded from the lien of the Indenture; and

      Whereas , all conditions have been met and all acts and things necessary have been done and performed to make the Indenture the valid and binding agreement of the Company and to substitute the Company for the Initial Mortgagor under the Indenture, and to vest the Company with each and every right and power of the Initial Mortgagor, including the right and power to issue bonds thereunder; and

      Whereas , the Company has subsequently executed and delivered, for purposes authorized under the Indenture, a Third Supplemental Indenture dated as of March 1, 1942, a Fourth Supplemental Indenture dated as of May 1, 1943, a Fifth Supplemental Indenture dated as of August 1, 1944, a Sixth Supplemental Indenture dated as of September 1, 1945, a Seventh Supplemental Indenture dated as of November 1, 1947, an Eighth Supplemental Indenture dated as of January 1, 1949, a Ninth Supplemental Indenture dated as of May 1, 1950, a Tenth Supplemental Indenture dated as of July 1, 1952, an Eleventh Supplemental Indenture dated as of January 1, 1954, a Twelfth Supplemental Indenture dated as of October 1, 1957, a Thirteenth Supplemental Indenture dated as of February 1, 1959, a Fourteenth Supplemental Indenture dated as of July 15, 1960, a Fifteenth Supplemental Indenture dated as of June 15, 1964, a Sixteenth Supplemental Indenture dated as of January 1, 1969, a Seventeenth Supplemental Indenture dated as of March 1, 1970, an Eighteenth Supplemental Indenture dated as of January 1, 1971, a Nineteenth Supplemental Indenture dated as of January 1, 1972, a Twentieth Supplemental Indenture dated as of February 1, 1974, a Twenty-First Supplemental Indenture dated as of August 1, 1974, a Twenty-Second Supplemental Indenture dated as of August 1, 1975, a Twenty-Third Supplemental Indenture dated as of January 1, 1977, a Twenty-Fourth Supplemental Indenture dated as of October 1, 1977, a Twenty-Fifth Supplemental Indenture dated as of September 1, 1978, a Twenty-Sixth Supplemental Indenture dated as of September 1, 1978, a Twenty-Seventh Supplemental Indenture dated as of March 1, 1979, a Twenty-Eighth Supplemental Indenture dated as of May 1, 1979, a Twenty-Ninth Supplemental Indenture dated as of March 1, 1980, a Thirtieth Supplemental Indenture dated as of August 1, 1980, a Thirty-First Supplemental Indenture dated as of February 1, 1981, a Thirty-Second Supplemental Indenture dated as of August 1, 1981, a Thirty-Third Supplemental Indenture dated as of December 1, 1981, a Thirty-Fourth Supplemental Indenture dated as of December 1, 1982, a Thirty-Fifth Supplemental Indenture dated as of March 30, 1984, a Thirty-Sixth Supplemental Indenture dated as of November 15, 1984, a Thirty-Seventh Supplemental Indenture dated as of August 15, 1985, a Thirty-Eighth Supplemental Indenture dated as of October 1, 1986, a Thirty-Ninth Supplemental Indenture dated as of March 15, 1987, a Fortieth Supplemental Indenture dated as of June 1, 1987, a Forty-First Supplemental Indenture dated as of June 15, 1988, a Forty-Second Supplemental Indenture dated as of August 1, 1988, a Forty-Third Supplemental Indenture dated as of September 15, 1989, a Forty-Fourth Supplemental Indenture dated as of March 15, 1990, a Forty-Fifth Supplemental Indenture dated as of March 15, 1990, a Forty-Sixth Supplemental Indenture dated as of June 1, 1990, a Forty-Seventh Supplemental Indenture dated as of July 15, 1991, a Forty-Eighth Supplemental Indenture dated as of July 15, 1992, a Forty-Ninth Supplemental Indenture dated as of February 15, 1993, a Fiftieth Supplemental Indenture dated as of February 15, 1993, a Fifty-First Supplemental Indenture dated as of February 1, 1994, a Fifty-Second Supplemental Indenture dated as of April 30, 1999, a Fifty-Third Supplemental Indenture dated as of June 15, 2001, a Fifty-Fourth Supplemental Indenture dated as of September 1, 2002, a Fifty-Fifth Supplemental Indenture dated as of February 15, 2003, and a Fifty-Sixth Supplemental Indenture dated as of December 1, 2004, each supplementing and amending the Indenture; and

      Whereas , the Thirty-Fifth Supplemental Indenture authorized and appointed LaSalle Bank National Association, a national banking association duly organized and existing under the law of the United States of America with its principal office in Chicago, Illinois and formerly named LaSalle National Bank, as Successor Trustee to The First National Bank of Chicago, which appointment was accepted, and all trust powers under the Indenture were thereby transferred from The First National Bank of Chicago to LaSalle Bank National Association; and

      Whereas , the Forty-Sixth Supplemental Indenture amended the Indenture to reflect a change in the name of the Company from Public Service Company of Indiana, Inc. to PSI Energy, Inc. effective as of April 20, 1990; and

      Whereas , as of August 21, 2008, the only bonds that have been heretofore issued under the Indenture which are now outstanding are $7,500,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series VV, Due July 15, 2026” and $70,000,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series WW, Due August 15, 2027” and $124,665,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series BBB, 8%, Due July 15, 2009” (such bonds being hereinafter referred to as the “Bonds of Series BBB”) and $53,055,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series CCC, 8.85%, Due January 15, 2022” and $38,000,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series DDD, 8.31%, Due September 1, 2032” and $23,000,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series FFF, Due March 1, 2031” and $24,600,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series GGG, Due March 1, 2019” and $35,000,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series HHH, Due April 1, 2022” and $77,125,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series III, Due December 1, 2039” and $77,125,000 aggregate principal amount of “PSI Energy, Inc. First Mortgage Bonds, Series JJJ, Due December 1, 2039”; and

      Whereas , in accordance with the provisions of Section 1 of Article XVIII of the Indenture, the Board of Directors has authorized the execution and delivery by the Company of a Fifty-Seventh Supplemental Indenture, substantially in the form of this Fifty-Seventh Supplemental Indenture, for the purpose of reflecting a change in the name of the Company from PSI Energy, Inc. to Duke Energy Indiana, Inc., for the purpose of creating a fifty-sixth series of bonds to be issued under the Indenture, to be known as “Duke Energy Indiana, Inc. First Mortgage Bonds, Series LLL, 6.35%, Due August 15, 2038” (such bonds being hereinafter referred to as the “Bonds of Series LLL”), and prescribing the form and substance of the Bonds of Series LLL and the terms, provisions and characteristics thereof, and for the purpose of adding to the covenants and agreements of the Company for the protection of the bondholders and of the trust estate, of providing the terms and conditions for the redemption of the Bonds of Series LLL, of adding certain other covenants and undertakings with respect to the Bonds of Series LLL and of making such changes in the Indenture as are deemed necessary or desirable and as are permitted by the Indenture; and

      Whereas , all conditions and requirements necessary to make this Fifty-Seventh Supplemental Indenture a valid, binding and legal instrument have been done, performed and fulfilled and the execution and delivery hereof have been in all respects duly authorized:

      Now, Therefore , in consideration of the premises, and of the acceptance and purchase of the Bonds of Series LLL by the holders and registered owners thereof, and of the sum of One Dollar ($1.00) duly paid by the Trustee to the Company, the receipt whereof is hereby acknowledged, and in accordance with and subject to the terms and provisions of the Indenture, the Company and the Trustee, respectively, have entered into, executed and delivered this Fifty-Seventh Supplemental Indenture for the uses and purposes hereinafter expressed, that is to say:

ARTICLE I.

First Mortgage Bonds, Series LLL, 6.35%, Due August 15, 2038

      Section 1 . There are hereby created a fifty-sixth series of bonds to be issued under and secured by the Indenture, to be designated as “Duke Energy Indiana, Inc. First Mortgage Bonds, Series LLL, 6.35%, Due August 15, 2038” (such series being the Bonds of Series LLL hereinbefore referred to).

      Section 2 . The following provisions shall apply to the Bonds of Series LLL.

     (a) The Bonds of Series LLL shall be issued in fully registered form only. However, except as provided elsewhere in this Section, the registered owner of all of the Bonds of Series LLL initially shall be The Depository Trust Company (“DTC”) or its nominee, and such Bonds of Series LLL initially shall be registered in the name of DTC or its nominee. Payment of the principal of or interest on Bonds of Series LLL registered in the name of DTC or its nominee shall be made in the manner specified in DTC’s rules and by-laws. DTC (and any successor securities depository) and its (or their) participating institutions (collectively “Participants”) shall maintain a book-entry registration and transfer system with respect to ownership of beneficial interests in the Bonds of Series LLL (the “Book-Entry System”).

     (b) The Bonds of Series LLL, initially shall be issued in the form of one or more authenticated, fully registered bonds for such series (each a “Global Security”) which (i) need not be in the form of a lithographed or engraved certificate, but may be typewritten or printed on ordinary paper or such paper as the Trustee may reasonably request, (ii) shall represent and be denominated in an amount equal to 100% of the aggregate principal amount of the Bonds of Series LLL issued under this Supplemental Indenture, (iii) shall be executed by the Company and authenticated by the Trustee in accordance with the provisions of the Indenture, (iv) shall be registered in the name of DTC or its nominee, and delivered to DTC or its nominee or a custodian therefor, and (v) shall contain the following legend on the face thereof:

Unless this certificate is presented by an authorized representative of The Depository Trust Company, a New York corporation (“DTC”), to issuer or its agent for registration of transfer, exchange or payment, and any certificate issued is registered in the name of Cede & Co. or in such other name as is requested by an authorized representative of DTC (and any payment is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered holder hereof, Cede & Co., has an interest herein.

Unless and until it is exchanged in whole or in part for Bonds of Series LLL in definitive certificated form, each Global Security representing the Bonds of Series LLL may not be transferred except as a whole by DTC to a nominee of DTC or by a nominee of DTC to DTC or another nominee of DTC or by DTC or any such nominee to a successor securities depository or a nominee of any such successor securities depository.

     (c) The Trustee and the Company may treat Cede & Co. or its nominee, or any successor securities depository or nominee thereof (collectively, the “Depository”) as the sole and exclusive owner of the Bonds of Series LLL, registered in its name for the purposes of payment of the principal or redemption price of or interest on the Bonds of Series LLL, giving any notice permitted or required to be given to holders of the Bonds of Series LLL, under the Indenture or this Supplemental Indenture, registering the transfer of the Bonds of Series LLL, obtaining any consent or other action to be taken by holders of the Bonds of Series LLL, and for all other purposes whatsoever and neither the Trustee nor the Company shall be affected by any notice to the contrary. Neither the Company nor the Trustee nor any registrar nor any paying agent shall have any responsibility or obligation to any Participant, any person claiming a beneficial ownership interest in the Bonds of Series LLL under or through the Depository or any Participant, or any other person which is not shown on the registration books as being a holder of the Bonds of Series LLL with respect to (i) the accuracy of any records maintained by the Depository or any Participant; (ii) the payment by the Depository to any Participant of any amount in respect of the principal or redemption price of or interest on the Bonds of Series LLL; (iii) the payment by any Participant to any owner of a beneficial ownership interest in the Bonds of Series LLL, in respect of the principal of or interest on the Bonds of Series LLL or (iv) any consent or other action taken by the Depository as owner of the Bonds of Series LLL. The Trustee shall pay all principal of and interest on the Bonds of Series LLL only to or upon the order of the registered holder or holders of the Bonds of Series LLL, as shown on the registration books, and all such payments shall be valid and effective to fully satisfy and discharge the Company’s obligations with respect to the principal or redemption price of and interest on the Bonds of Series LLL, to the extent of the sum or sums so

paid. No person other than a holder of the Bonds of Series LLL, as shown on the registration books of DTC, shall receive an authenticated Bond evidencing the obligation of the Company to make payment of the principal of and interest on the Bonds of Series LLL, pursuant to the Indenture and this Supplemental Indenture. Upon delivery by DTC to the Trustee of written notice to the effect that DTC has determined to substitute a new nominee for Cede & Co, and subject to the provisions of the Indenture and this Supplemental Indenture, the word “Cede & Co.”, as used in this Supplemental Indenture, shall refer to each new nominee of DTC.

     (d) In the event that after the occurrence of an event of default that has not been cured or waived, holders of a majority in aggregate principal amount of the beneficial interests in the Bonds of Series LLL, as reflected in the books and records of the Depository, notify the Trustee, through the Depository or any Participant, that the continuation of the Book-Entry System is no longer in the best interests of such holders of beneficial interests in the Bonds of such Series, then the Trustee shall notify the Depository and the Company, and the Depository will notify the Participants of the availability through the Depository of definitive certificated Bonds of such Series. In such event, the Company shall execute, and the Trustee, upon receipt of a written order of the Company, signed by its President or a Vice President and by its Treasurer, Assistant Treasurer, Secretary or Assistant Secretary (an “Issuer Order”), for the authentication and delivery of definitive certificated Bonds of Series LLL, will authenticate and deliver Bonds of such Series in definitive certificated form, in any authorized denominations, all pursuant to the provisions of the Indenture, to the person or persons specified to the Trustee in writing by the Depository in the aggregate principal amount of the applicable Global Security or Securities and in exchange for such Global Security or Securities.

     (e) If at any time the Depository notifies the Company that it is unwilling or unable to continue as Depository for the Bonds of Series LLL, or if at any time the Depository shall no longer be registered as a clearing agency in good standing under the Securities Exchange Act of 1934, as amended, or other applicable statute or regulation, the Company may appoint a successor Depository with respect to the Bonds of such Series. If a successor Depository for the Bonds of such Series is not appointed by the Company within 90 days after the Company receives such notice or becomes aware of such condition, the Company will execute, and the Trustee, upon receipt of an Issuer Order for the authentication and delivery of definitive certificated Bonds of Series LLL, will authenticate and deliver Bonds of such Series in definitive certificated form, in any authorized denominations, all pursuant to the provisions of the Indenture, to the person or persons specified to the Trustee in writing by the Depository in the aggregate principal amount of the applicable Global Security or Securities and in exchange for such Global Security or Securities.

     (f) The Company may at any time and in its sole discretion determine that the Bonds of Series LLL shall no longer be represented by a Global Security or Securities. In such event the Company will execute, and the Trustee, upon receipt of an Issuer Order for the authentication and delivery of definitive certificated Bonds of such Series, will authenticate and deliver Bonds of Series