FIFTH SUPPLEMENTAL INDENTURE

FIFTH SUPPLEMENTAL INDENTURE

FROM

WISCONSIN PUBLIC SERVICE CORPORATION

TO

U.S. BANK NATIONAL ASSOCIATION
(SUCCESSOR TO FIRSTAR BANK, NATIONAL ASSOCIATION AND
FIRSTAR BANK, MILWAUKEE, N.A., NATIONAL ASSOCIATION)

TRUSTEE

_________________

Dated as of December 1, 2006

SUPPLEMENTAL TO INDENTURE
Dated as of December 1, 1998

Senior Debt Securities

        This FIFTH SUPPLEMENTAL INDENTURE is made as of the 1 ^st day of December, 2006, by and between WISCONSIN PUBLIC SERVICE CORPORATION, a corporation duly organized and existing under the laws of the State of Wisconsin (the "Company"), and U.S. BANK NATIONAL ASSOCIATION (successor to Firstar Bank, National Association and Firstar Bank Milwaukee, N.A., National Association), a national banking association duly organized and existing under the laws of the United States, as trustee (the "Trustee").

RECITALS OF THE COMPANY:

        WITNESSETH: that

        The Company has heretofore executed and delivered its Indenture (hereinafter referred to as the "Indenture"), made as of December 1, 1998; and

        Section 3.1 of the Indenture provides that Securities may be issued from time to time in series pursuant to a supplemental indenture specifying the terms of each series of Securities; and

        The Company desires to establish a series of Securities to be designated "Senior Notes, 5.55% Series Due December 1, 2036 (the "Securities of the Series due 2036"); and

        Section 10.1 of the Indenture provides that the Company and the Trustee may enter into indentures supplemental thereto for the purposes, among others, of establishing the form or terms of Securities of any series and adding to the covenants of the Company; and

        The execution and delivery of this Fifth Supplemental Indenture (herein, this "Supplemental Indenture") has been duly authorized by a Board Resolution;

        NOW, THEREFORE, this Supplemental Indenture

        WITNESSETH, that, in order to set forth the terms and conditions upon which Securities of the Series due 2036 are, and are to be, authenticated, issued and delivered, and in consideration of the sum of one dollar duly paid to it by the Trustee at the execution of this Supplemental Indenture, the receipt whereof is hereby acknowledged, the Company covenants and agrees with the Trustee for the equal and proportionate benefit of the respective Holders from time to time of such Securities as follows:

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ARTICLE I
RELATION TO INDENTURE; DEFINITIONS

SECTION 1.1

        This Supplemental Indenture constitutes an integral part of the Indenture.

SECTION 1.2

        For all purposes of this Supplemental Indenture:

        (a)     Capitalized terms used but not otherwise defined herein shall have the respective meanings assigned to such terms in the Indenture;

        (b)     All references herein to Articles and Sections, unless otherwise specified, refer to the corresponding Articles and Sections of this Supplemental Indenture; and

        (c)     The terms "hereof," "herein," "hereby," "hereto," "hereunder," and "herewith" refer to this Supplemental Indenture.

ARTICLE II
THE SECURITIES

        There is hereby established a series of Securities pursuant to Section 3.01 of the Indenture as follows:

        (a)     The title of the Securities of the series hereby established is "Senior Notes, 5.55% Series Due December 1, 2036."

        (b)     The aggregate principal amount of the Securities of the Series due 2036 which may be authenticated and delivered under the Indenture (except for Securities authenticated and delivered upon registration of transfer of, or in exchange for, or in lieu of other Securities of such series pursuant to Sections 2.05, 3.04, 3.05, 3.06, 10.06 or 12.07) shall initially be limited to One Hundred and Twenty-Five Million Dollars ($125,000,000), subject to the right of the Company to reopen the Securities of the Series due 2036 for the issuance of additional Securities of the Series due 2036 on the terms and subject to the conditions specified below.

        (c)     The Company shall have the right to reopen the Securities of the Series due 2036 for the issuance of additional Securities of such series ("Additional Securities of the Series due 2036"). The issuance of any Additional Securities of the Series due 2036 shall constitute a further issuance of, and will be consolidated with, the Securities of the Series due 2036, so as to form a single series. The Additional Securities of the Series due 2036 shall be substantially in the form hereinafter recited, but may contain such changes as may be appropriate to reflect their date or dates of issuance. Where appropriate references to the Securities of the Series due 2036 in this Supplemental Indenture shall be deemed to include the Additional Securities of the Series due 2036.

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        (d)     The Securities of the Series due 2036 are to be issued in permanent global form without coupons. The beneficial owners of interests in such permanent Global Security or Securities may not exchange such interests for Securities of such series other than in the manner provided in Section 2.05 of the Indenture. The Depositary for the Securities of the Series due 2036 shall be The Depositary Trust Company.

        (e)     The Stated Maturity of the Securities of the Series due 2036 is December 1, 2036.

        (f)     The Securities of the Series due 2036 shall bear interest at the rate of 5.55% per annum, and such interest shall accrue from December 1, 2006 (or from the most recent Interest Payment Date to which interest on the Securities of the Series due 2036 has been paid or provided for). The Interest Payment Dates for the Securities of the Series due 2036 shall be June 1 and December 1 in each year commencing June 1, 2007, and the Regular Record Date for the interest payable on any Interest Payment Date shall be the fifteenth day (whether or not a Business Day) preceding such Interest Payment Date.

        (g)     Principal of and interest on the Securities of the Series due 2036 shall be payable in U.S. Dollars at the Corporate Trust Office of the Trustee.

        (h)     The Securities of the Series due 2036 are subject to redemption in whole at any time or in part from time to time at the option and direction of the Company at a Redemption Price equal to the greater of (i) 100% of the principal amount of the Securities of the Series due 2036 to be redeemed or (ii) the sum of the present values of the remaining scheduled payments of principal and interest thereon (exclusive of interest accrued to the date of redemption), discounted to the Redemption Date on a semi-annual basis (assuming a 360 day year of twelve 30-day months) at the Treasury Rate as hereinafter defined, plus fifteen hundredths of one percent (0.15%) plus in each case accrued and unpaid interest to the Redemption Date. Such Redemption Date shall be set forth in an Officers’ Certificate delivered to the Trustee on or before the Redemption Date and upon which the Trustee may conclusively rely.

        For purposes of this paragraph (h):

        "Treasury Rate" means, with respect to any Redemption Date, the rate per annum equal to the semiannual equivalent yield to maturity or interpolated (on a day count basis) of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for such Redemption Date.

        "Comparable Treasury Issue" means the United States Treasury security or securities selected by an Independent Investment Banker as having an actual or interpolated maturity comparable to the remaining term of the Notes that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the Notes.

        "Independent Investment Banker" means one of the Reference Treasury Dealers appointed by the Trustee after consultation with the Company.

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        "Comparable Treasury Price" means, with respect to any Redemption Date, (i) the average of the Reference Treasury Dealer Quotations for the Redemption Date, after excluding the highest and lowest Reference Treasury Dealer Quotations for the Redemption Date, or (ii) if the Trustee obtains fewer than four Reference Treasury Dealer Quotations, the average of all the quotations which the Trustee obtains.

        "Reference Treasury Dealer Quotations" means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Trustee, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Trustee by such Reference Treasury Dealer at 3:30 p.m., New York time, on the third business day preceding such Redemption Date.

        "Reference Treasury Dealer" means any primary U.S. Government securities dealer in the United States (a "Primary Treasury Dealer") selected by the Company.

        (i)     The Securities of the Series due 2036 shall not be subject to any sinking fund and shall not be redeemable at the option of the Holders thereof.

        (j)     The Securities of the Series due 2036 shall initially be issued in whole in the form of one or more Global Securities. If individual securities of the Series due 2036 are issued under the conditions specified in Section 2.05 of the Indenture, individual certificates will be issued in denominations of $1,000 or any integral multiple thereof.

        (k)     The Related Series of Collateral Bonds being delivered to the Trustee in connection with the issuance of the Securities of the Series due 2036 is the Company’s First Mortgage Bonds, Collateral Series E.

        Such Securities of the Series due 2036 and Additional Securities of the Series due 2036, if any, shall be initially authenticated and delivered from time to time upon delivery to the Trustee of the documents required by Section 3.1 of the Indenture and the form of Securities for the Securities of the Series due 2036 and Additional Securities of the Series due 2036, if any, substantially in the form of Security attached hereto as Appendix I, which is incorporated herein by reference.

ARTICLE III
TRANSFER OF COLLATERAL BONDS

        The Company hereby issues, delivers and transfers to the Trustee in connection with the issuance of the Securities of the Series due 2036 One Hundred and Twenty-Five Million Dollars ($125,000,000) aggregate principal amount of a related issue of Collateral Bonds of the Company designated "First Mortgage Bonds, Collateral Series E" (each, a "Related Issue," as to the series of Securities it secures, and, the "Collateral Bonds"), which has been fully registered in the name of the Trustee in such capacity, to be held in trust for the benefit of the Holders from time to time of the Related Issue of Securities and, if such transfer does not constitute a sale of the Collateral Bonds to the Trustee, the Company hereby grants a perfected security interest in the Collateral Bonds for the benefit of such Holders, in each case as security for any and all obligations of the Company under the Indenture, this Supplemental Indenture and the Related Issue of Securities, including but not limited to (1) the full and prompt payment of the interest on, principal of, and premium, if any, on such Related Issue of Securities when and as the same shall become due and payable in accordance with the terms and provisions of the Indenture and this Supplemental Indenture and such Related Issue of Securities, either at the Stated Maturity thereof, upon acceleration of the maturity thereof or upon redemption, and (2) the full and prompt payment of any interest on such Related Issue of Securities when and as the same shall become due and payable in accordance with the terms and provisions of the Indenture and this Supplemental Indenture and such Related Issue of Securities. The Trustee shall enforce all of its rights under the First Mortgage Indenture as a holder of each Related Issue of Collateral Bonds transferred to it as provided in this Article III for the benefit of the Holders of the respective Related Issue of Securities and the proceeds of the enforcement of such rights shall be applied by the Trustee to satisfy the Company’s obligations under the Indenture, this Supplemental Indenture, and such Related Issue of Securities.

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        The Company shall make payments of the principal of, and premium or interest on each of the Collateral Bonds to the Trustee, which payments shall be applied by the Trustee to satisfaction of all obligations then due on the respective Related Issue of Securities.

        The Collateral Bonds shall not be sold or transferred by the Trustee until the earlier of the Release Date or the prior retirement of the Related Issue of Securities through redemption, repurchase or otherwise. Without limiting the generality of the foregoing, in no event shall the Collateral Bonds be sold or become the absolute property of any person in violation of the applicable provisions of Section 201.04(2) of the Wisconsin Statutes or any successor statutory provision. The "Release Date" shall be the date that all First Mortgage Bonds of the Company issued and outstanding under the First Mortgage Indenture, other than the Collateral Bonds, have been retired (at, before or after the maturity thereof) through payment, redemption or otherwise, provided that no Default or Event of Default has occurred and, at such time, is continuing under the Indenture.

        A copy of the form of Collateral Bond is attached hereto as Appendix II and its terms are hereby incorporated by reference herein.

ARTICLE IV
MISCELLANEOUS

SECTION 4.1

        The Trustee has accepted the amendment of the Indenture effected by this Supplemental Indenture and agrees to execute the trust created by the Indenture as hereby amended, but only upon the terms and conditions set forth in the Indenture, including the terms and provisions defining and limiting the liabilities and responsibilities of the Trustee, and without limiting the generality of the foregoing, the Trustee shall not be responsible in any manner whatsoever for or with respect of any of the recitals or statements contained herein, all of which recitals or statements are made solely by the Company, or for or with respect to (a) the validity or sufficiency of this Supplemental Indenture or any of the terms or provisions hereof, (b) the proper authorization hereof by the Company by corporate action or otherwise, and (c) the due execution hereof by the Company.

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SECTION 4.2

        This Supplemental Indenture shall be construed in connection with and as a part of the Indenture.

SECTION 4.3

        (a)     If any provision of this Supplemental Indenture conflicts with another provision of the Indenture required to be included in indentures qualified under the Trust Indenture Act of 1939, as amended (as enacted prior to the date of this Supplemental Indenture), by any of the provisions of Sections 310 to 317, inclusive, of said act, such required provision shall control.

        (b)     In case any one or more of the provisions contained in this Supplemental Indenture or in the Securities issued hereunder should be invalid, illegal, or unenforceable in any respect, the validity, legality and enforceability of the remaining provisions contained herein and therein shall not in any way be affected, impaired, prejudiced or disturbed thereby.

SECTION 4.4

        Whenever in this Supplemental Indenture either of the parties hereto is named or referred to, such name or reference shall be deemed to include the successors or assigns of such party, and all the covenants and agreements contained in this Supplemental Indenture by or on behalf of the Company or by or on behalf of the Trustee shall bind and inure to the benefit of the respective successors and assigns of such parties, whether so expressed or not.

SECTION 4.5

        (a)     This Supplemental Indenture may be simultaneously executed in several counterparts, and all such counterparts executed and delivered, each as an original, shall constitute but one and the same instrument.

        (b)     The descriptive headings of the several Articles of this Supplemental Indenture were formulated, used and inserted in this Supplemental Indenture for convenience only and shall not be deemed to affect the meaning or construction of any of the provisions hereof.

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        IN WITNESS WHEREOF, WISCONSIN PUBLIC SERVICE CORPORATION has caused this Supplemental Indenture to be executed by its Chairman, Chief Executive Officer, President, Vice Chairman or a Vice President, or any other officer selected by the Board of Directors, and its corporate seal to be hereunto affixed, duly attested by its Secretary or an Assistant Secretary, and U.S. BANK NATIONAL ASSOCIATION, as Trustee as aforesaid, has caused this Supplemental Indenture to be executed by one of its authorized signatories, as of December 1, 2006.

ATTEST:

/s/ Barth J. Wolf
      Barth J. Wolf
      Secretary

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APPENDIX I

$___________

CUSIP: No. 976843-[BE1]

        THIS SECURITY IS A GLOBAL SECURITY REGISTERED IN THE NAME OF THE DEPOSITARY (REFERRED TO HEREIN) OR A NOMINEE THEREOF AND UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR THE INDIVIDUAL SECURITIES REPRESENTED HEREBY, THIS GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITARY TO A NOMINEE OF THE DEPOSITARY OR BY A NOMINEE OF THE DEPOSITARY TO THE DEPOSITARY OR ANOTHER NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITARY.*

        UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY TRUST COMPANY, A NEW YORK CORPORATION (55 WATER STREET, NEW YORK, NEW YORK), TO THE TRUSTEE 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 THE DEPOSITARY TRUST COMPANY AND ANY PAYMENT IS MADE TO CEDE & CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.*

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WISCONSIN PUBLIC SERVICE CORPORATION
Senior Note, 5.55% Series Due December 1, 2036

        WISCONSIN PUBLIC SERVICE CORPORATION, a corporation duly organized and existing under the laws of Wisconsin (herein called the "Company," which term includes any successor corporation unde