THIS FOURTH SUPPLEMENTAL INDENTURE, dated as of [ • ] is between SOUTHWESTERN PUBLIC SERVICE COMPANY, a New Mexico corporation (hereinafter called the “Issuer” or the “Company”), having its principal office at Tyler at Sixth Street, Amarillo, Texas 79101, and JPMORGAN CHASE BANK, N.A, as successor to THE CHASE MANHATTAN BANK, as Trustee (hereinafter called the “Trustee”), having its office at 4 New York Plaza, 15th Floor, New York, New York 10004.

Recitals of the Issuer

The Issuer and the Trustee have heretofore entered into an Indenture, dated as of February 1, 1999, a First Supplemental Indenture, dated as of March 1, 1999, a Second Supplemental Indenture dated as of October 1, 2001 and a Third Supplemental Indenture dated as of October 1, 2003 (such Indenture, as supplemented by the First Supplemental Indenture, the Second Supplemental Indenture, the Third Supplemental Indenture and this Supplemental Indenture, being hereinafter referred to as the “Indenture”), relating to the issuance at any time or from time to time of its Securities on terms to be specified at the time of issuance. Terms used and not otherwise defined herein shall (unless the context otherwise clearly requires) have the respective meanings given to them in the Indenture.

The Indenture provides in Article Two thereof that, prior to the issuance of Securities of any series, the form of such Securities and the terms applicable to such series shall be established in, or pursuant to, the authority granted in a resolution of the Board of Directors (delivered to the Trustee in the form of a Bond Resolution) or established in one or more indentures supplemental thereto.

The Issuer desires by this Supplemental Indenture, among other things, to establish the form of the Securities of a series, to be titled Series  [ • ] Senior Notes, [ • ] % due [ • ] of the Issuer, and to establish the terms applicable to such series, pursuant to Sections 2.01 and 10.01 of the Indenture. The Issuer has duly authorized the execution and delivery of this Supplemental Indenture.

Article Ten of the Indenture provides that the Issuer, when authorized by a resolution of its Board of Directors, and the Trustee may from time to time and at any time amend the Indenture without the consent of Securityholders for certain purposes enumerated in Section 10.01 thereof, including purposes set forth in subsection (4) of said Section 10.01.

The execution and delivery of this Supplemental Indenture by the parties hereto are in all respects authorized by the provisions of the Indenture. All things necessary have been done to make this Supplemental Indenture a valid agreement of the Issuer, in accordance with its terms.

NOW, THEREFORE, THIS FOURTH SUPPLEMENTAL INDENTURE WITNESSETH:

For and in consideration of the premises, it is mutually covenanted and agreed, as follows:

ARTICLE I.

ESTABLISHMENT OF SERIES [ • ] NOTES, [•]% DUE [•]

Section 1.01. The title of the series of the Securities established by this Supplemental Indenture shall be Series  [ • ] Senior Notes, [ • ] % due [ • ] of the Issuer (hereinafter called the “Series  [ • ] Notes”). The Series  [ • ] Notes shall be issued in registered form substantially in the form set forth in Exhibit A hereto (which is hereby incorporated herein and made a part hereof), subject to changes in the form thereof made by the Issuer and acceptable to the Trustee.

Section 1.02. The Series  [ • ] Notes shall be limited to $ [ • ] in aggregate principal amount.

Section 1.03. The Series  [ • ] Notes may be issued in whole or in part as one or more Global Securities and The Depository Trust Company, or a nominee thereof, shall be the Depository for such Global Security or Global Securities. The Depository for such Global Security or Global Securities representing Series  [ • ] Notes may surrender one or more Global Securities representing Series  [ • ] Notes in exchange in whole or in part for individual Series  [ • ] Notes on such terms as are acceptable to the Issuer and such Depository and otherwise subject to the terms of Section 2.12 of the Indenture.

Section 1.04. The Issuer hereby appoints, or confirms the appointment of, JPMorgan Chase Bank, N.A., as the initial Trustee, Transfer Agent and Paying Agent, subject to the provisions of the Indenture with respect to resignation, removal and succession, and subject, further, to the right of the Issuer to appoint additional agents (including Paying Agents).

Section 1.05. The terms of the Series  [ • ] Notes shall be as set forth in Exhibit A hereto, and shall include the payment and other terms reflected on the Series  [ • ] Notes as actually executed, authenticated and delivered under the Indenture.

ARTICLE II.

MISCELLANEOUS

Section 2.01. The recitals contained herein shall be taken as the statements of the Issuer, and the Trustee assumes no responsibility for the correctness of the same. The Trustee makes no representation as to the validity or sufficiency of this Supplemental Indenture.

Section 2.02. The Indenture, as supplemented by this Supplemental Indenture, is in all respects hereby adopted, ratified and confirmed.

Section 2.03. This Supplemental Indenture may be executed in any number of counterparts, and on separate counterparts, each of which shall be an original; but such counterparts shall together constitute but one and the same instrument.

Section 2.04. If any provision of this Supplemental Indenture limits, qualifies or conflicts with the duties imposed by any of Sections 310 to 317, inclusive, of the Trust Indenture

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Act of 1939, as amended by the Trust Indenture Reform Act of 1990, through operation of Section 318(c), such imposed duties shall control.

Section 2.05. The Article headings herein are for convenience only and shall not affect the interpretation hereof.

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IN WITNESS WHEREOF, the parties hereto have caused this Fourth Supplemental Indenture to be duly executed, and their respective corporate seals to be hereunto affixed and attested as of the [ • ] day of [ • ] , [ • ] .

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EXHIBIT A

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