Document:

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                                                                 EXHIBIT 4(b)(3)

                             PUBLIC SERVICE COMPANY
                                   OF COLORADO

                                       TO

                      U.S. BANK TRUST NATIONAL ASSOCIATION,

                                                               AS TRUSTEE

                              ---------------------

                          SUPPLEMENTAL INDENTURE NO. 12

                            Dated as of March 1, 2003

                          Supplemental to the Indenture
                           dated as of October 1, 1993

                              ---------------------

                  Establishing the Securities of Series No. 11,
             designated First Collateral Trust Bonds, Series No. 11

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         SUPPLEMENTAL INDENTURE NO. 12, dated as of March 1, 2003, between
PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and existing
under the laws of the State of Colorado (hereinafter sometimes called the
"Company"), and U.S. BANK TRUST NATIONAL ASSOCIATION (FORMERLY FIRST TRUST OF
NEW YORK, NATIONAL ASSOCIATION), a national banking association, as successor
trustee (hereinafter sometimes called the "Trustee") to Morgan Guaranty Trust
Company of New York under the Indenture, dated as of October 1, 1993
(hereinafter called the "Original Indenture"), as previously supplemented and as
further supplemented by this Supplemental Indenture No. 12. The Original
Indenture and any and all indentures and all other instruments supplemental
thereto are hereinafter sometimes collectively called the "Indenture".

                             RECITALS OF THE COMPANY

         The Original Indenture was authorized, executed and delivered by the
Company to provide for the issuance from time to time of its Securities (such
term and all other capitalized terms used herein without definition having the
meanings assigned to them in the Original Indenture), to be issued in one or
more series as contemplated therein, and to provide security for the payment of
the principal of and premium, if any, and interest, if any, on the Securities.

         The Company has heretofore executed and delivered to the Trustee the
Supplemental Indentures referred to in Schedule A hereto for the purpose of
establishing a series of bonds and appointing the successor Trustee.

         The Company desires to establish a series of Securities to be
designated "First Collateral Trust Bonds, Series No. 11", such series of
Securities to be hereinafter sometimes called "Series No. 11".

         The Company has duly authorized the execution and delivery of this
Supplemental Indenture No. 12 to establish the Securities of Series No. 11 and
has duly authorized the issuance of such Securities; and all acts necessary to
make this Supplemental Indenture No. 12 a valid agreement of the Company, and to
make the Securities of Series No. 11 valid obligations of the Company, have been
performed.

                                GRANTING CLAUSES

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE NO. 12 WITNESSETH, that, in
consideration of the premises and of the purchase of the Securities by the
Holders thereof, and in order to secure the payment of the principal of and
premium, if any, and interest, if any, on all Securities from time to time
Outstanding and the performance of the covenants contained therein and in the
Indenture and to declare the terms and conditions on which such Securities are
secured, the Company hereby grants, bargains, sells, releases, conveys, assigns,
transfers, mortgages, pledges, sets over and confirms to the Trustee, and grants
to the Trustee a security interest in, the following:

                              GRANTING CLAUSE FIRST

                  All right, title and interest of the Company, as of the date
         of the execution and delivery of this Supplemental Indenture No. 12, in
         and to property (other than Excepted Property), real, personal and
         mixed and wherever situated, in any case used or to be used in or in
         connection with the Electric Utility Business (whether or not such use
         is the sole use of such property), including without limitation (a) all
         lands, easements, servitudes, licenses, permits, rights of way and
         other rights and interests in or relating to real property used or to
         be used in or in connection with the Electric Utility Business or
         relating to the occupancy or use of such real property, subject
         however, to the exceptions and exclusions set forth in clause (a) of
         Granting Clause First of the Original Indenture;

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         (b) all plants, generators, turbines, engines, boilers, fuel handling
         and transportation facilities, air and water pollution control and
         sewage and solid waste disposal facilities and other machinery and
         facilities for the generation of electric energy; (c) all switchyards,
         lines, towers, substations, transformers and other machinery and
         facilities for the transmission of electric energy; (d) all lines,
         poles, conduits, conductors, meters, regulators and other machinery and
         facilities for the distribution of electric energy; (e) all buildings,
         offices, warehouses and other structures used or to be used in or in
         connection with the Electric Utility Business; (f) all pipes, cables,
         insulators, ducts, tools, computers and other data processing and/or
         storage equipment and other equipment, apparatus and facilities used or
         to be used in or in connection with the Electric Utility Business; (g)
         any or all of the foregoing properties in the process of construction;
         and (h) all other property, of whatever kind and nature, ancillary to
         or otherwise used or to be used in conjunction with any or all of the
         foregoing or otherwise, directly or indirectly, in furtherance of the
         Electric Utility Business;

                             GRANTING CLAUSE SECOND

                  Subject to the applicable exceptions permitted by Section
         810(c), Section 1303 and Section 1305 of the Original Indenture, all
         property (other than Excepted Property) of the kind and nature
         described in Granting Clause First which may be hereafter acquired by
         the Company, it being the intention of the Company that all such
         property acquired by the Company after the date of the execution and
         delivery of this Supplemental Indenture No. 12 shall be as fully
         embraced within and subjected to the Lien hereof as if such property
         were owned by the Company as of the date of the execution and delivery
         of this Supplemental Indenture No. 12;

                             GRANTING CLAUSE FOURTH

                  All other property of whatever kind and nature subjected or
         required to be subjected to the Lien of the Indenture by any of the
         provisions thereof;

                                EXCEPTED PROPERTY

                  Expressly excepting and excluding, however, from the Lien and
         operation of the Indenture all Excepted Property of the Company,
         whether now owned or hereafter acquired;

         TO HAVE AND TO HOLD all such property, real, personal and mixed, unto
the Trustee, its successors in trust and their assigns forever;

         SUBJECT, HOWEVER, to (a) Liens existing at the date of the execution
and delivery of the Original Indenture (including, but not limited to, the Lien
of the PSCO 1939 Mortgage), (b) as to property acquired by the Company after the
date of the execution and delivery of the Original Indenture, Liens existing or
placed thereon at the time of the acquisition thereof (including, but not
limited to, the Lien of any Class A Mortgage and purchase money Liens), (c)
Retained Interests and (d) any other Permitted Liens, it being understood that,
with respect to any property which was at the date of execution and delivery of
the Original Indenture or thereafter became or hereafter becomes subject to the
Lien of any Class A Mortgage, the Lien of the Indenture shall at all times be
junior, subject and subordinate to the Lien of such Class A Mortgage;

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         IN TRUST, NEVERTHELESS, for the equal and proportionate benefit and
security of the Holders from time to time of all Outstanding Securities without
any priority of any such Security over any other such Security;

         PROVIDED, HOWEVER, that the right, title and interest of the Trustee in
and to the Mortgaged Property shall cease, terminate and become void in
accordance with, and subject to the conditions set forth in, Article Nine of the
Original Indenture, and if, thereafter, the principal of and premium, if any,
and interest, if any, on the Securities shall have been paid to the Holders
thereof, or shall have been paid to the Company pursuant to Section 603 of the
Original Indenture, then and in that case the Indenture shall terminate, and the
Trustee shall execute and deliver to the Company such instruments as the Company
shall require to evidence such termination; otherwise the Indenture, and the
estate and rights thereby granted shall be and remain in full force and effect;
and

         THE PARTIES HEREBY FURTHER COVENANT AND AGREE as follows:

                                   ARTICLE ONE

                           SECURITIES OF SERIES NO. 11

         There are hereby established the Securities of Series No. 11, which
shall have the terms and characteristics set forth below (the lettered
subdivisions set forth below corresponding to the lettered subdivisions of
Section 301 of the Original Indenture):

         (a) the title of the Securities of such series shall be "First
         Collateral Trust Bonds, Series No. 11"; provided, however, that, at any
         time after the PSCO 1939 Mortgage shall have been satisfied and
         discharged, the Company shall have the right, without any consent or
         other action by the Holders of such Securities, to change such title in
         such manner as shall be deemed by the Company to be appropriate to
         reflect such satisfaction and discharge, such change to be evidenced in
         an Officer's Certificate;

         (b) the Securities of Series No. 11 shall be initially authenticated
         and delivered in the aggregate principal amount of $250,000,000;

         (c) interest on the Securities of Series No. 11 shall be payable to the
         Persons in whose names such Securities are registered at the close of
         business on the Regular Record Date for such interest, except as
         otherwise expressly provided in the form of such Securities attached as
         Exhibit A hereto;

         (d) the principal of the Securities of Series No. 11 shall be payable
         on March 1, 2013, the Stated Maturity.

         (e) the Securities of Series No. 11 shall bear interest at a rate of
         4.875% per annum; interest shall accrue on the Securities of Series No.
         11 from March 14, 2003, or the most recent date to which interest has
         been paid or duly provided for; the Interest Payment Dates for such
         Securities shall be March 1 and September 1 in each year, commencing
         September 1, 2003, and the Regular Record Dates with respect to the
         Interest Payment Dates for such Securities shall be February 15 and
         August 15 in each year, respectively (whether or not a Business Day);

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         (f) the Corporate Trust Office of U.S. Bank Trust National Association
         in New York, New York shall be the place at which (i) the principal of,
         premium, if any, and interest, if any, on the Securities of Series No.
         11 shall be payable, (ii) registration of transfer of such Securities
         may be effected, (iii) exchanges of such Securities may be effected and
         (iv) notices and demands to or upon the Company in respect of such
         Securities and the Indenture may be served; and U.S. Bank Trust
         National Association shall be the Security Registrar for such
         Securities; provided, however, that the Company reserves the right to
         change, by one or more Officer's Certificates, any such place or the
         Security Registrar; and provided, further, that the Company reserves
         the right to designate, by one or more Officer's Certificates, its
         principal office in Denver, Colorado as any such place or itself as the
         Security Registrar;

         (g) the Securities of Series No. 11 shall be redeemable at the option
         of the Company at any time prior to maturity, in whole or in part, at a
         redemption price equal to the greater of (i) 100% of the principal
         amount thereof to be redeemed, or (ii) the sum of the present values of
         the remaining scheduled payments of principal and interest on such
         Securities to be redeemed, discounted to the Redemption Date on a
         semi-annual basis (assuming a 360-day year consisting of twelve 30-day
         months) at the Treasury Yield plus 20 basis points, plus in each case,
         accrued and unpaid interest to the Redemption Date. For purposes
         hereof, the following defined terms shall have the meaning ascribed to
         them:

                  "Treasury Yield" means, for any Redemption Date, the rate per
         annum equal to the semi-annual equivalent yield to maturity 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 the Redemption Date.

                  "Comparable Treasury Issue" means the United States Treasury
         security selected by an Independent Investment Banker as having a
         maturity comparable to the remaining term of the Securities of Series
         No. 11 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 Securities of Series No. 11.

                  "Comparable Treasury Price" means, for any Redemption Date,
         (i) the average of the bid and asked prices for the Comparable Treasury
         Issue (expressed in each case as a percentage of its principal amount)
         on the third Business Day preceding the Redemption Date, as set forth
         in the daily statistical release (or any successor release) published
         by the Federal Reserve Bank of New York and designated "Composite 3:30
         p.m. Quotations for U.S. Government Securities" or (ii) if that release
         (or any successor release) is not published or does not contain those
         prices on that Business Day, (A) 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 (B) if the Trustee obtains fewer than four Reference Treasury
         Dealer Quotations, the average of all of the Quotations.

                  "Independent Investment Banker" means Banc One Capital
         Markets, Inc. or its successor or, if such firm or its successor is
         unwilling or unable to select the Comparable Treasury Issue, one of the
         remaining Reference Treasury Dealers appointed by the Trustee after
         consultation with the Company.

                  "Reference Treasury Dealer" means (i) each of Banc One Capital
         Markets, Inc., UBS Warburg LLC and any other Primary Treasury Dealer
         designated by, and not affiliated with,

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         Bank One Capital Markets, Inc., UBS Warburg LLC and their respective
         successors, provided, however, that if either of the foregoing or any
         of their designees ceases to be a Primary Treasury Dealer, the Company
         will appoint another Primary Treasury Dealer as a substitute and (ii)
         any other Primary Treasury Dealer selected by the Company.

                  "Primary Treasury Dealer" means any primary U.S. Government
         securities dealer in the United States.

                  "Reference Treasury Dealer Quotations" means, for each
         Reference Treasury Dealer and any Redemption Date, the average, as
         determined by the Independent Investment Banker, 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
         Independent Investment Banker by the Reference Treasury Dealer at 5:00
         p.m. on the third Business Day preceding the Redemption Date.

         (h) not applicable;

         (i) not applicable;

         (j) not applicable;

         (k) not applicable;

         (l) not applicable;

         (m) not applicable;

         (n) not applicable;

         (o) any Securities of Series No. 11 which are presented to the Company
         and/or the Trustee for exchange pursuant to a Registered Exchange Offer
         in accordance with the terms thereof shall be exchanged for New
         Securities of equal principal amount upon surrender to the Company
         and/or the Trustee of the Securities of Series No. 11 to be exchanged;
         provided, however, that the Securities of Series No. 11 so surrendered
         for exchange shall be duly endorsed and accompanied by a letter of
         transmittal or written instrument of transfer in form satisfactory to
         the Company, duly executed by the registered holder thereof or its
         attorney who shall be duly authorized in writing to execute such
         document. Whenever any Securities of Series No. 11 are so surrendered
         for exchange, the Company shall execute, and the Trustee shall
         authenticate and deliver to and in the name of each registered holder
         that has properly tendered its Securities of Series No. 11 for
         exchange, the same aggregate principal amount of New Securities as the
         Securities of Series No. 11 that have been so surrendered. For purposes
         hereof, the following defined terms shall have the meaning ascribed to
         them:

                  "Registered Exchange Offer" means the proposed offer of the
         Company to issue and deliver to the Holders of the Securities of Series
         No. 11 that are not prohibited by any law or policy of the Commission
         from participating in such offer, in exchange for the Securities of
         Series No. 11, a like aggregate principal amount of the New Securities.

                  "New Securities" means debt securities of the Company
        identical in all material respects to the Securities of Series No. 11
        presented for exchange pursuant to the Registered Exchange

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         Offer (except that the transfer restrictions shall be modified or
         eliminated, as appropriate) and to be issued under the Indenture.

         (p) not applicable;

         (q) (i) the Securities of Series No. 11 (1) if issued to "qualified
             institutional buyers" (each a "QIB"), as defined in Rule 144A under
             the Securities Act of 1933, as amended (the "Securities Act") in
             reliance on Rule 144A under the Securities Act shall be issued in
             the form of one or more Rule 144A global bonds or (2) if issued in
             offshore transactions to non-U.S. persons in reliance on Regulation
             S under the Securities Act shall be issued in the form of one or
             more Regulation S global bonds, and, in the case of either (1) or
             (2) above, shall be deposited on behalf of the Holders of the
             Securities of Series No. 11 represented thereby with the Trustee,
             as custodian for the securities depositary, shall be registered in
             the name of the securities depositary or its nominee and the
             aggregate principal amount of Securities of Series No. 11 so issued
             may from time to time be increased or decreased by adjustments made
             on the records of the Trustee and the securities depositary or its
             nominee. For purposes hereof, (A) "Rule 144A global bonds" means
             one or more global bonds deposited with a custodian for, and
             registered in the name of a nominee of, a securities depository,
             interests in which will be held for the benefit of purchasers of
             bonds in transactions under Rule 144A, and (B) "Regulation S global
             bonds" means one or more global bonds deposited with a custodian
             for, and registered in the name of a nominee of, a securities
             depositary, interests in which will be held for the benefit of
             purchasers of the bonds in offshore transactions under Regulation
             S;

             (ii) except as provided in subparagraph (q)(v) hereof, the
             Securities of Series No. 11 are to be initially registered in the
             name of Cede & Co., as nominee for The Depository Trust Company
             (the "Depositary"). Subject to subparagraphs (o) and (q)(iii), (iv)
             and (v) hereof, such Securities shall not be transferable or
             exchangeable, nor shall any purported transfer be registered,
             except as follows:

                  (A) such Securities may be transferred in whole, and
                  appropriate registration of transfer effected, if such
                  transfer is by such nominee to the Depositary, or by the
                  Depositary to another nominee thereof, or by any nominee of
                  the Depositary to any other nominee thereof, or by the
                  Depositary or any nominee thereof to any successor securities
                  depositary or any nominee thereof; and

                  (B) such Securities may be exchanged for definitive Securities
                  registered in the respective names of the beneficial holders
                  thereof, and, subject to subparagraph (iii), (iv) and (v)
                  below, thereafter shall be transferable without restriction,
                  if:

                           (1) the Depositary, or any successor securities
                           depositary, shall have notified the Company and the
                           Trustee that it is unwilling or unable to continue to
                           act as securities depositary with respect to such
                           Securities or the Depositary has ceased to be a
                           clearing agency registered under the Securities
                           Exchange Act of 1934, as amended, and the Trustee
                           shall not have been notified by the Company within
                           ninety (90) days of the

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                           identity of a successor securities depositary with
                           respect to such Securities;

                           (2) the Company shall have delivered to the Trustee a
                           Company Order to the effect that such Securities
                           shall be so exchangeable on and after a date
                           specified therein; or

                           (3) (a) an Event of Default shall have occurred and
                           be continuing, (b) the Trustee shall have given
                           notice of such Event of Default pursuant to Section
                           1102 of the Original Indenture and (c) there shall
                           have been delivered to the Company and the Trustee an
                           Opinion of Counsel to the effect that the interests
                           of the beneficial owners of such Securities in
                           respect thereof will be materially impaired unless
                           such owners become Holders of definitive Securities.

         (iii)    all Securities of Series No. 11 and all beneficial
         interests in one or more Securities of Series No. 11, and all
         Securities issued upon registration of, transfer of, or in exchange
         for, any such Securities (other than New Securities or Securities sold
         pursuant to an effective registration statement under the Securities
         Act or Securities issued, directly or indirectly, upon registration of
         transfer of, or in exchange for, any such Securities), shall be
         restricted securities within the meaning of Rule 144 under the
         Securities Act (collectively, "Restricted Securities") and shall be
         subject to the restrictions on transfer provided in the legends set
         forth on the Restricted Securities. The registered Holder of each
         Restricted Security, by such registered Holder's acceptance thereof,
         agrees to be bound by such restrictions on transfer. All Restricted
         Securities shall bear on their faces the applicable legends limiting
         transferability set forth on the form of the Securities of Series
         No.11.

                  Each registered Holder of a beneficial interest in a global
         bond that is a Restricted Security will be deemed to have represented
         and agreed to offer, sell, pledge or otherwise transfer such beneficial
         interest only in accordance with the legend set forth on the face of
         the Restricted Securities.

                  Subject to the restrictions on transfer and exchange set forth
         herein and in the Indenture, the holder of any Securities issued
         hereunder may transfer or exchange such Securities in whole or in part
         by surrendering them at the Corporate Trust Office of the Trustee or
         its agent, together with (A), an executed instrument of assignment and
         transfer (in the case of a transfer) or a written request for exchange
         (in the case of exchange), and, in the case of Securities of Series No.
         11 that are Restricted Securities, a certificate substantially in the
         form of Exhibit B hereto, and (B) additional certifications and
         evidence that such transfer or exchange is in compliance with the
         Securities Act and the restrictions on transfer set forth in such bonds
         as may be required pursuant to the terms of this Supplemental Indenture
         No. 12.

         (iv)     the following provisions shall apply with respect to any
         proposed transfer of a Rule 144A global bond or a beneficial interest
         therein prior to (x) the date which is two years (or such shorter
         period of time as permitted by Rule 144(k) of the Securities Act) after
         the later of the original issue date of the Securities and the last
         date on which the Company or any "affiliate" (as defined in Rule 144
         under the Securities Act) of the Company was the owner of the Security
         (or any

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         predecessor of the Security) or (y) such later date, if any, as may be
         required by applicable law:

                  (A) a transfer of a Rule 144A global bond or a beneficial
                  interest therein to a QIB in accordance with Rule 144A shall
                  be made upon the representation of the transferee that it is
                  purchasing the Security for its own account or an account with
                  respect to which it exercises sole investment discretion and
                  that it and any such account is a QIB and is aware that the
                  sale to it is being made in reliance on Rule 144A and
                  acknowledges that it has received such information regarding
                  the Company as it has requested pursuant to Rule 144A or has
                  determined not to request such information and that it is
                  aware that the transferor is relying upon its foregoing
                  representations in order to claim the exemption from
                  registration provided by Rule 144A;

                  (B) a transfer of a Rule 144A global bond or a beneficial
                  interest therein in accordance with Regulation S shall be made
                  upon receipt by the Trustee or its agent of a certificate
                  substantially in the form set forth in Exhibit C annexed
                  hereto from the proposed transferor and, if requested by the
                  Company or the Trustee, the delivery of an opinion of counsel,
                  certifications and/or other information satisfactory to each
                  of them.

         (v) the following provisions shall apply with respect to any proposed
         transfer of a Regulation S global bond or a beneficial interest therein
         prior to (x) the date which is two years (or such shorter period of
         time as permitted by Rule 144(k) of the Securities Act) after the later
         of the original issue date of the Securities and the last date on which
         the Company or any "affiliate" (as defined in Rule 144 under the
         Securities Act) of the Company was the owner of the Security (or any
         predecessor of the Security) or (y) such later date, if any, as may be
         required by applicable law:

                  (A) a transfer of a Regulation S global bond or a beneficial
                  interest therein to a QIB in accordance with Rule 144A shall
                  be made upon the representation of the transferee that it is
                  purchasing the bond for its own account or an account with
                  respect to which it exercises sole investment discretion and
                  that it and any such account is a QIB and is aware that the
                  sale to it is being made in reliance on Rule 144A and
                  acknowledges that it has received such information regarding
                  the Company as it has requested pursuant to Rule 144A or has
                  determined not to request such information and that it is
                  aware that the transferor is relying upon its foregoing
                  representations in order to claim the exemption from
                  registration provided by Rule 144A;

                  (B) a transfer of a Regulation S global bond or a beneficial
                  interest therein in accordance with Regulation S shall be made
                  upon receipt by the Trustee or its agent of a certificate
                  substantially in the form set forth in Exhibit C annexed
                  hereto from the proposed transferor and, if requested by the
                  Company or the Trustee, the delivery of an opinion of counsel,
                  certifications and/or other information satisfactory to each
                  of them.

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                                    Prior to or on the expiration of the 40-day
                           "distribution compliance period" within the meaning
                           of Rule 903 of Regulation S under the Securities Act
                           ("Distribution Compliance Period"), beneficial
                           interests in a Regulation S global bond may only be
                           held through the operator of the Euroclear System
                           ("Euroclear") or Clearstream Banking, a societe
                           anonyme ("Clearstream") (as indirect participants in
                           the Depositary) or another agent member of Euroclear
                           or Clearstream acting for and on behalf of them,
                           unless exchanged for interests in the Rule 144A
                           global bond in accordance with the certification
                           requirements hereof.

                                    During the Distribution Compliance Period,
                           interests in the Regulation S global bond, if any,
                           may be exchanged for interests in the Rule 144A
                           global bond only in accordance with the certification
                           requirements described in clause (A) of this
                           subparagraph (q)(v).

         (r) not applicable;

         (s) no service charge shall be made for the registration of transfer or
         exchange of the Securities of Series No. 11; provided, however, that
         the Company may require payment of a sum sufficient to cover any tax or
         other governmental charge payable in connection with the exchange or
         transfer;

         (t) not applicable;

         (u) (i) If the Company shall have caused the Company's indebtedness in
             respect of any Securities of Series No. 11 to have been satisfied
             and discharged prior to the Maturity of such Securities, as
             provided in Section 901 of the Original Indenture, the Company
             shall, promptly after the date of such satisfaction and discharge,
             give a notice to each Person who was a Holder of any of such
             Securities on such date stating (A)(1) the aggregate principal
             amount of such Securities and (2) the aggregate amount of any money
             (other than amounts, if any, deposited in respect of accrued
             interest on such Securities) and the aggregate principal amount of,
             the rate or rates of interest on, and the aggregate fair market
             value of, any Eligible Obligations deposited pursuant to Section
             901 of the Original Indenture with respect to such Securities and
             (B) that the Company will provide (and the Company shall promptly
             so provide) to such Person, or any beneficial owner of such
             Securities holding through such Person (upon written request to the
             Company sent to an address specified in such notice), such other
             information as such Person or beneficial owner, as the case may be,
             reasonably may request in order to enable it to determine the
             federal income tax consequences to it resulting from the
             satisfaction and discharge of the Company's indebtedness in respect
             of such Securities. Thereafter, the Company shall, within
             forty-five (45) days after the end of each calendar year, give to
             each Person who at any time during such calendar year was a Holder
             of such Securities a notice containing (X) such information as may
             be necessary to enable such Person to report its income, gain or
             loss for federal income tax purposes with respect to such
             Securities or the assets held on deposit in respect thereof during
             such calendar year or the portion thereof during which such Person
             was a Holder of such Securities, as the case may be (such
             information to be set forth for such calendar year as a whole and
             for each month during such year) and (Y) a statement to the effect
             that the Company will provide (and the

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             Company shall promptly so provide) to such Person, or any
             beneficial owner of such Securities holding through such Person
             (upon written request to the Company sent to an address specified
             in such notice), such other information as such Person or
             beneficial owner, as the case may be, reasonably may request in
             order to enable it to determine its income, gain or loss for
             federal income tax purposes with respect to such Securities or such
             assets for such year or portion thereof, as the case may be. The
             obligation of the Company to provide or cause to be provided
             information for purposes of income tax reporting by any Person as
             described in the first two sentences of this paragraph shall be
             deemed to have been satisfied to the extent that the Company has
             provided or caused to be provided substantially comparable
             information pursuant to any requirements of the Internal Revenue
             Code of 1986, as amended from time to time (the "Code") and United
             States Treasury regulations thereunder.

             (ii) Notwithstanding the provisions of subparagraph (i) above, the
             Company shall not be required to give any notice specified in such
             subparagraph or to otherwise furnish any of the information
             contemplated therein if the Company shall have delivered to the
             Trustee an Opinion of Counsel to the effect that the Holders of
             such Securities will not recognize income, gain or loss for federal
             income tax purposes as a result of the satisfaction and discharge
             of the Company's indebtedness in respect of such Securities and
             such Holders will be subject to federal income taxation on the same
             amounts and in the same manner and at the same times as if such
             satisfaction and discharge had not occurred.

             (iii) Anything in this clause (u) to the contrary notwithstanding,
             the Company shall not be required to give any notice specified in
             subparagraph (i) or to otherwise furnish the information
             contemplated therein or to deliver any Opinion of Counsel
             contemplated by subparagraph (ii) if the Company shall have caused
             Securities of Series No. 11 to be deemed to have been paid for
             purposes of the Indenture, as provided in Section 901 of the
             Original Indenture, but shall not have effected the satisfaction
             and discharge of its indebtedness in respect of such Securities
             pursuant to such Section.

         (v) The Securities of Series No. 11 shall be substantially in the form
         attached hereto as Exhibit A and shall have such further terms as are
         set forth in such form.

                                   ARTICLE TWO

                            MISCELLANEOUS PROVISIONS

         This Supplemental Indenture No. 12 is a supplement to the Original
Indenture. As previously supplemented and further supplemented by this
Supplemental Indenture No. 12, the Original Indenture is in all respects
ratified, approved and confirmed, and the Original Indenture, all previous
supplements thereto and this Supplemental Indenture No. 12 shall together
constitute one and the same instrument.

                                       10
<PAGE>

                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture No. 12 to be duly executed as of the day and year first
above written.

                                  PUBLIC SERVICE COMPANY OF COLORADO

                                  By:      /S/ BENJAMIN G.S. FOWKE III
                                       -----------------------------------------

                                       Name:   Benjamin G. S. Fowke III
                                       Title:  Vice President and Treasurer

STATE OF MINNESOTA       )
                         ) ss.:
CITY OF MINNEAPOLIS      )

         On the 6th day of March, 2003, before me personally came Benjamin G. S.
Fowke III to me known, who, being by me duly sworn, did depose and say that he
is a Vice President and Treasurer of Public Service Company of Colorado, one of
the corporations described in and which executed the foregoing instrument; and
that he signed his name thereto by authority of the Board of Directors of said
corporation.

                                         /S/ ELLEN C. CHRISTOFFERSON
                                    --------------------------------------------
                                    Name: Ellen C. Christofferson
                                    Notary Public, State of Minnesota
               [SEAL]               Commission Expires:  January 31, 2005

                                       11
<PAGE>

                                    U.S. BANK TRUST NATIONAL ASSOCIATION,
                                                             Trustee

                                    By:          /S/ IGNAZIO TAMBURELLO
                                          --------------------------------------

                                          Name:      Ignazio Tamburello
                                          Title:     Assistant Vice President

STATE OF NEW YORK                 )
                                  ) ss.:
CITY AND COUNTY OF NEW YORK       )

         On the 6th day of March, 2003, before me personally came Ignazio
Tamburello, to me known, who, being by me duly sworn, did depose and say that he
is an Assistant Vice President of U.S. Bank Trust National Association, the
banking association described in and which executed the foregoing instrument;
and that he signed his name thereto by authority of the Board of Directors of
said banking association.

                                         /S/ ROUBA FAKIH
                                    --------------------------------------------
                                    Name:  Rouba Fakih
                                    Notary Public, State of New York

                                    Commission Expires: February 20, 2007

                                           [SEAL]

                                       12
<PAGE>

                                                                       EXHIBIT A

                                FORM OF SECURITY

                   (See legend at the end of this Security for
                  restrictions on transfer and change of form)

                       PUBLIC SERVICE COMPANY OF COLORADO
                   First Collateral Trust Bond, Series No. 11

        Original Interest Accrual Date          March 14, 2003
                        Interest Rate:          4.875%
                      Stated Maturity:          March 1, 2013
               Interest Payment Dates:          March 1 and September 1
                 Regular Record Dates:          February 15 and August 15

                    This Security is not a Discount Security
              within the meaning of the within-mentioned Indenture

                    -----------------------------------------

Principal Amount                                                 Registered No.
$                                                                CUSIP

         PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and
existing under the laws of the State of Colorado (herein called the "Company,"
which term includes any successor corporation under the Indenture referred to
below), for value received, hereby promises to pay to

, or registered assigns, the principal sum of

Dollars on the Stated Maturity specified above, and to pay interest thereon from
the Original Interest Accrual Date specified above or from the most recent
Interest Payment Date to which interest has been paid or duly provided for,
semi-annually in arrears on the Interest Payment Dates specified above in each
year, commencing September 1, 2003, and at Maturity, at the Interest Rate per
annum specified above, until the principal hereof is paid or duly provided for.
The interest so payable, and paid or duly provided for, on any Interest Payment
Date shall, as provided in such Indenture, be paid to the Person in whose name
this Security (or one or more Predecessor Securities) is registered at the close
of business on the Regular Record Date specified above (whether or not a
Business Day) next preceding such Interest Payment Date. Notwithstanding the
foregoing, interest payable at Maturity shall be paid to the Person to whom
principal shall be paid. Except as otherwise provided in said Indenture, any
such interest not so paid or duly provided for shall forthwith cease to be
payable to the Holder on such Regular Record Date and may either be paid to the
Person in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on a Special Record Date for the payment of
such Defaulted Interest to be fixed by the Trustee, notice of which shall be
given to Holders of Securities of this series not less

                                  EXHIBIT A-1
<PAGE>

than 15 days prior to such Special Record Date, or be paid in such other manner
as permitted by the Indenture.

         Payment of the principal of this Security and interest hereon at
Maturity shall be made upon presentation of this Security at the Corporate Trust
Office of U.S. Bank Trust National Association, in New York, New York or at such
other office or agency as may be designated for such purpose by the Company from
time to time. Payment of interest on this Security (other than interest at
Maturity) shall be made by check mailed to the address of the Person entitled
thereto as such address shall appear in the Security Register, except that if
such Person shall be a securities depositary, such payment may be made by such
other means in lieu of check as shall be agreed upon by the Company, the Trustee
and such Person. Payment of the principal of and interest on this Security, as
aforesaid, shall be made in such coin or currency of the United States of
America as at the time of payment shall be legal tender for the payment of
public and private debts.

         This Security is one of a duly authorized issue of securities of the
Company (herein called the "Securities"), issued and issuable in one or more
series under and equally secured by an Indenture, dated as of October 1, 1993
(such Indenture as originally executed and delivered and as supplemented or
amended from time to time thereafter, together with any constituent instruments
establishing the terms of particular Securities, being herein called the
"Indenture"), between the Company and U.S. Bank Trust National Association
(formerly First Trust of New York, National Association) as successor trustee
(herein called the "Trustee," which term includes any successor trustee under
the Indenture), to which Indenture and all indentures supplemental thereto
reference is hereby made for a description of the property mortgaged, pledged
and held in trust, the nature and extent of the security and the respective
rights, limitations of rights, duties and immunities of the Company, the Trustee
and the Holders of the Securities thereunder and of the terms and conditions
upon which the Securities are, and are to be, authenticated and delivered and
secured. The acceptance of this Security shall be deemed to constitute the
consent and agreement by the Holder hereof to all of the terms and provisions of
the Indenture. This Security is one of the series designated above.

         If any Interest Payment Date or the Stated Maturity shall not be a
Business Day (as hereinafter defined), payment of the amounts due on this
Security on such date may be made on the next succeeding Business Day; and, if
such payment is made or duly provided for on such Business Day, no interest
shall accrue on such amounts for the period from and after such Interest Payment
Date or Stated Maturity, as the case may be, to such Business Day.

         This Security shall be redeemable at the option of the Company at any
time prior to maturity, in whole or in part, at a redemption price equal to the
greater of (i) 100% of the principal amount hereof to be redeemed, or (ii) the
sum of the present values of the remaining scheduled payments of principal and
interest on this Security being redeemed, discounted to the Redemption Date on a
semi-annual basis (assuming a 360-day year consisting of twelve 30-day months)
at the Treasury Yield plus 20 basis points, plus in each case, accrued and
unpaid interest to the Redemption Date. For purposes hereof, the following
defined terms shall have the meaning ascribed to them:

         "Treasury Yield" means, for any Redemption Date, the rate per annum
equal to the semi-annual equivalent yield to maturity 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
the Redemption Date.

         "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity comparable to
the remaining term of the Securities

                                  EXHIBIT A-2
<PAGE>

of Series No. 11 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 Securities
of Series No. 11.

         "Comparable Treasury Price" means, for any Redemption Date, (i) the
average of the bid and asked prices for the Comparable Treasury Issue (expressed
in each case as a percentage of its principal amount) on the third Business Day
preceding the Redemption Date, as set forth in the daily statistical release (or
any successor release) published by the Federal Reserve Bank of New York and
designated "Composite 3:30 p.m. Quotations for U.S. Government Securities" or
(ii) if that release (or any successor release) is not published or does not
contain those prices on that Business Day, (A) 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 (B)
if the Trustee obtains fewer than four Reference Treasury Dealer Quotations, the
average of all of the Quotations.

         "Independent Investment Banker" means Banc One Capital Markets, Inc. or
its successor or, if such firm or its successor is unwilling or unable to select
the Comparable Treasury Issue, one of the remaining Reference Treasury Dealers
appointed by the Trustee after consultation with the Company.

         "Reference Treasury Dealer" means (i) each of Banc One Capital Markets,
Inc., UBS Warburg LLC and any other Primary Treasury Dealer designated by, and
not affiliated with, Banc One Capital Markets, Inc., UBS Warburg LLC and their
respective successors, provided, however, that if either of the foregoing or any
of their designees ceases to be a Primary Treasury Dealer, the Company will
appoint another Primary Treasury Dealer as a substitute and (ii) any other
Primary Treasury Dealer selected by the Company.

         "Primary Treasury Dealer" means any primary U.S. Government securities
dealer in the United States.

         "Reference Treasury Dealer Quotations" means, for each Reference
Treasury Dealer and any Redemption Date, the average, as determined by the
Independent Investment Banker, 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 Independent Investment Banker by the Reference Treasury
Dealer at 5:00 p.m. on the third Business Day preceding the Redemption Date.

         If an Event of Default shall occur and be continuing, the principal of
this Security may be declared due and payable in the manner and with the effect
provided in the Indenture.

         The Indenture permits, with certain exceptions as therein provided, the
Trustee to enter into one or more supplemental indentures for the purpose of
adding any provisions to, or changing in any manner or eliminating any of the
provisions of, the Indenture with the consent of the Holders of not less than a
majority in aggregate principal amount of the Securities of all series then
Outstanding under the Indenture, considered as one class; provided, however,
that if there shall be Securities of more than one series Outstanding under the
Indenture and if a proposed supplemental indenture shall directly affect the
rights of the Holders of Securities of one or more, but less than all, of such
series, then the consent only of the Holders of a majority in aggregate
principal amount of the Outstanding Securities of all series so directly
affected, considered as one class, shall be required; and provided, further,
that if the Securities of any series shall have been issued in more than one
Tranche and if the proposed supplemental indenture shall directly affect the
rights of the Holders of Securities of one or more, but less than all, of such
Tranches, then the consent only of the Holders of a majority in aggregate
principal amount of the Outstanding Securities of all Tranches so directly
affected, considered as one class, shall be required; and

                                  EXHIBIT A-3
<PAGE>

provided, further, that the Indenture permits the Trustee to enter into one or
more supplemental indentures for limited purposes without the consent of any
Holders of Securities. The Indenture also contains provisions permitting the
Holders of a majority in principal amount of the Securities then Outstanding, on
behalf of the Holders of all Securities, to waive compliance by the Company with
certain provisions of the Indenture and certain past defaults under the
Indenture and their consequences. Any such consent or waiver by the Holder of
this Security shall be conclusive and binding upon such Holder and upon all
future Holders of this Security and of any Security issued upon the registration
of transfer hereof or in exchange therefor or in lieu hereof, whether or not
notation of such consent or waiver is made upon this Security.

         As provided in the Indenture and subject to certain limitations therein
set forth, this Security or any portion of the principal amount hereof will be
deemed to have been paid for all purposes of the Indenture and to be no longer
Outstanding thereunder, and, at the election of the Company, the Company's
entire indebtedness in respect thereof will be satisfied and discharged, if
there has been irrevocably deposited with the Trustee or any Paying Agent (other
than the Company), in trust, money in an amount which will be sufficient and/or
Eligible Obligations, the principal of and interest on which when due, without
regard to any reinvestment thereof, will provide moneys which, together with
moneys so deposited, will be sufficient, to pay when due the principal of and
interest on this Security when due.

         As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office of U.S. Bank Trust National Association, in New York, New York or such
other office or agency as may be designated by the Company from time to time,
duly endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Company and the Security Registrar duly executed by, the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Securities of this series of authorized denominations and of like tenor
and aggregate principal amount, will be issued to the designated transferee or
transferees.

         The Securities of this series are issuable only as registered
Securities, without coupons, and in denominations of $1,000 and integral
multiples thereof. As provided in the Indenture and subject to certain
limitations therein set forth, Securities of this series are exchangeable for a
like aggregate principal amount of Securities of the same series, of any
authorized denominations, as requested by the Holder surrendering the same, and
of like tenor upon surrender of the Security or Securities to be exchanged at
the office of U.S. Bank Trust National Association, in New York, New York or
such other office or agency as may be designated by the Company from time to
time.

         Any Securities of this series which are presented to the Company and/or
the Trustee for exchange pursuant to a Registered Exchange Offer in accordance
with the terms thereof shall be exchanged for New Securities of equal principal
amount upon surrender to the Company and/or the Trustee of the Securities to be
exchanged; provided, however, that the Securities of this series so surrendered
for exchange shall be duly endorsed and accompanied by a letter of transmittal
or written instrument of transfer in form satisfactory to the Company, duly
executed by the registered holder thereof or its attorney who shall be duly
authorized in writing to execute such document. Whenever any Securities of this
series are so surrendered for exchange, the Company shall execute, and the
Trustee shall authenticate and deliver to and in the name of each registered
holder that has properly tendered its Securities for exchange, the same
aggregate principal amount of New Securities as the Securities of this series
that have been so surrendered. For purposes hereof, the following defined terms
shall have the meaning ascribed to them:

         "Registered Exchange Offer" means the proposed offer of the Company to
issue and deliver to the Holders of the Securities of this series that are not
prohibited by any law or policy of the Commission

                                  EXHIBIT A-4
<PAGE>

from participating in such offer, in exchange for the Securities of this series,
a like aggregate principal amount of the New Securities.

         "New Securities" means debt securities of the Company identical in all
material respects to the Securities of this series presented for exchange
pursuant to the Registered Exchange Offer (except that the transfer restrictions
shall be modified or eliminated, as appropriate) and to be issued under the
Indenture.

         No service charge shall be made for any such registration of transfer
or exchange, but the Company may require payment of a sum sufficient to cover
any tax or other governmental charge payable in connection therewith.

         Prior to due presentment of this Security for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name this Security is registered as the absolute owner
hereof for all purposes, whether or not this Security be overdue, and neither
the Company, the Trustee nor any such agent shall be affected by notice to the
contrary.

         The Indenture and the Securities shall be governed by and construed in
accordance with the laws of the State of New York.

         As used herein "Business Day" means any day, other than a Saturday or
Sunday, which is not a day on which banking institutions or trust companies in
The City of New York, New York or other city in which is located any office or
agency maintained for the payment of principal or interest on this Security, are
authorized or required by law, regulation or executive order to remain closed.
All other terms used in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.

         As provided in the Indenture, no recourse shall be had for the payment
of the principal of or interest on any Securities, or any part thereof, or for
any claim based thereon or otherwise in respect thereof, or of the indebtedness
represented thereby, or upon any obligation, covenant or agreement under the
Indenture, against, and no personal liability whatsoever shall attach to, or be
incurred by, any incorporator, shareholder, officer or director, as such, past,
present or future of the Company or of any predecessor or successor corporation
(either directly or through the Company or a predecessor or successor
corporation), whether by virtue of any constitutional provision, statute or rule
of law, or by the enforcement of any assessment or penalty or otherwise; it
being expressly agreed and understood that the Indenture and all the Securities
are solely corporate obligations and that any such personal liability is hereby
expressly waived and released as a condition of, and as part of the
consideration for, the execution of the Indenture and the issuance of the
Securities.

         Unless the certificate of authentication hereon has been executed by
the Trustee or an Authenticating Agent by manual signature, this Security shall
not be entitled to any benefit under the Indenture or be valid or obligatory for
any purpose.

                                  EXHIBIT A-5
<PAGE>

         IN WITNESS WHEREOF, the Company has caused this instrument to be duly
executed and its corporate seal to be hereunto affixed and attested.

                                    PUBLIC SERVICE COMPANY OF COLORADO

                                    By:
                                       -----------------------------------------
                                         [Title]

Attest:
       ---------------------------
             [Title]

                          CERTIFICATE OF AUTHENTICATION

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

Dated:
       ---------------------------

            U.S. BANK TRUST            OR              U.S. BANK TRUST
         NATIONAL ASSOCIATION,                      NATIONAL ASSOCIATION,
              as Trustee                                 as Trustee

By:                                            By:
       ---------------------------                ------------------------------
         Authorized Officer                        AS AUTHENTICATING AGENT

                                               By:
                                                  ------------------------------
                                                       Authorized Officer

         UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE COMPANY 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 OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

                                     ------

                                  EXHIBIT A-6
<PAGE>

                                 RESTRICTED NOTE

         [THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
         1933, AS AMENDED (THE "SECURITIES ACT"). THE HOLDER HEREOF, BY
         PURCHASING THIS SECURITY, AGREES FOR THE BENEFIT OF THE COMPANY THAT
         THIS SECURITY MAY NOT BE RESOLD, PLEDGED OR OTHERWISE TRANSFERRED OTHER
         THAN (A)(1) TO THE COMPANY, (2) IN A TRANSACTION ENTITLED TO AN
         EXEMPTION FROM REGISTRATION PROVIDED BY RULE 144 UNDER THE SECURITIES
         ACT, (3) SO LONG AS THIS SECURITY IS ELIGIBLE FOR RESALE PURSUANT TO
         RULE 144A UNDER THE SECURITIES ACT ("RULE 144A"), TO A PERSON WHOM THE
         SELLER REASONABLY BELIEVES IS A QUALIFIED INSTITUTIONAL BUYER WITHIN
         THE MEANING OF RULE 144A PURCHASING FOR ITS OWN ACCOUNT OR FOR THE
         ACCOUNT OF A QUALIFIED INSTITUTIONAL BUYER TO WHOM NOTICE IS GIVEN THAT
         THE RESALE, PLEDGE OR OTHER TRANSFER IS BEING MADE IN RELIANCE ON RULE
         144A, (4) OUTSIDE THE UNITED STATES IN A TRANSACTION MEETING THE
         REQUIREMENTS OF REGULATION S UNDER THE SECURITIES ACT, (5) IN
         ACCORDANCE WITH ANOTHER APPLICABLE EXEMPTION FROM THE REGISTRATION
         REQUIREMENTS OF THE SECURITIES ACT (AND BASED UPON AN OPINION OF
         COUNSEL ACCEPTABLE TO THE COMPANY) OR (6) PURSUANT TO A REGISTRATION
         STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE UNDER THE SECURITIES ACT
         AND (B) IN EACH CASE IN ACCORDANCE WITH APPLICABLE SECURITIES LAWS OF
         EACH STATE OF THE UNITED STATES. THE HOLDER HEREOF, BY PURCHASING THIS
         SECURITY, REPRESENTS AND AGREES FOR THE BENEFIT OF THE COMPANY THAT IT
         IS (1) A QUALIFIED INSTITUTIONAL BUYER WITHIN THE MEANING OF RULE 144A
         OR (2) A NON-U.S. PERSON OUTSIDE THE UNITED STATES WITHIN THE MEANING
         OF REGULATION S UNDER THE SECURITIES ACT.]

         [THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
         1933, AS AMENDED (THE "SECURITIES ACT"), AND ACCORDINGLY, MAY NOT BE
         OFFERED OR SOLD WITHIN THE UNITED STATES OR TO OR FOR THE ACCOUNT OR
         BENEFIT OF, U.S. PERSONS EXCEPT AS SET FORTH IN THE PRECEDING
         PARAGRAPH. BY ITS ACQUISITION HEREOF, THE HOLDER (1) REPRESENTS THAT IT
         IS NOT A U.S. PERSON AND IS ACQUIRING THIS SECURITY IN AN OFFSHORE
         TRANSACTION, (2) BY ITS ACCEPTANCE HEREOF AGREES TO OFFER, SELL OR
         OTHERWISE TRANSFER SUCH SECURITY, PRIOR TO THE DATE (THE RESALE
         RESTRICTION TERMINATION DATE) WHICH IS TWO YEARS AFTER THE LATER OF THE
         ORIGINAL ISSUE DATE HEREOF AND THE LAST DATE ON WHICH THE COMPANY OR
         ANY AFFILIATE OF THE COMPANY WAS THE OWNER OF THIS SECURITY (OR ANY
         PREDECESSOR OF SUCH SECURITY), ONLY AS SET FORTH IN THE PRECEDING
         PARAGRAPH, SUBJECT TO THE COMPANY'S AND THE TRUSTEE'S RIGHTS PRIOR TO
         ANY SUCH OFFER, SALE OR TRANSFER TO REQUIRE THE DELIVERY OF AN OPINION
         OF COUNSEL, CERTIFICATION AND/OR OTHER INFORMATION SATISFACTORY TO EACH
         OF THEM (FORMS OF WHICH MAY BE OBTAINED FROM THE COMPANY OR THE
         TRUSTEE) COMPLETED AND DELIVERED BY THE TRANSFEROR TO THE COMPANY AND
         THE TRUSTEE.](1)

                                  -------------

----------
(1) To be inserted only in Regulation S global bond.

                                  EXHIBIT A-7
<PAGE>

         FOR VALUE RECEIVED the undersigned hereby sells, assigns and transfers
unto

--------------------------------------------------------------------------------
     [please insert social security or other identifying number of assignee]

--------------------------------------------------------------------------------
            [please print or typewrite name and address of assignee]

--------------------------------------------------------------------------------

the within Security of PUBLIC SERVICE COMPANY OF COLORADO and does hereby
irrevocably constitute and appoint __________________________________ ,
Attorney, to transfer said Security on the books of the within-mentioned
Company, with full power of substitution in the premises.

Dated:
      ---------------------------

             ------------------------------------------------------

         Notice: The signature to this assignment must correspond with the name
         as written upon the face of the Security in every particular without
         alteration or enlargement or any change whatsoever.

                                  EXHIBIT A-8
<PAGE>

                                                                       EXHIBIT B

                        [Form of Transferor Certificate]

                CERTIFICATE TO PUBLIC SERVICE COMPANY OF COLORADO
        AND TRUSTEE FIRST COLLATERAL TRUST BONDS, SERIES NO. 11 DUE 2013

This is to certify that as of the date hereof with respect to U.S. $____________
principal amount of the above-captioned securities presented or
surrendered on the date hereof (the "Surrendered Bonds") for registration of
transfer or for exchange where the securities issuable upon such exchange are to
be registered in a name other than that of the undersigned holder (each such
transaction being a "transfer"), the undersigned holder of the Surrendered Bonds
represents and certifies for the benefit of Public Service Company of Colorado
and U.S. Bank Trust National Association, as Trustee, that the transfer of
Surrendered Bonds associated with such transfer complies with the restrictive
legend set forth on the face of the Surrendered Bonds for the reason checked
below:

[ ]      The Surrendered Bonds are being transferred to a person whom we
         reasonably believe is a "qualified institutional buyer" (as defined in
         Rule 144A under the Securities Act of 1933) (a "QIB") that purchases
         for its own account or for the account of a QIB to whom notice is given
         that the resale, pledge or transfer is being made in reliance on Rule
         144A under the Securities Act; or

[ ]      The transfer of the Surrendered Bonds complies with Rule 144 under the
         Securities Act;(1) or

[ ]      The transfer of the Surrendered Bonds complies with another applicable
         exemption from the registration requirements of the Securities Act.(1)

                                         [Name of holder]

                Dated:                  ,
                       -----------------  -------
         [To be dated the date of presentation or surrender]

----------
(1) These transfers may require an opinion of counsel.

                                  EXHIBIT B-1
<PAGE>

                                                                       EXHIBIT C

                   [Form of Regulation S Transfer Certificate]

                                                                          [date]
Public Service Company of Colorado
1225 17th Street
Denver, Colorado  80202
[Attention:                         ]
           -------------------------

U.S. Bank Trust National Association
100 Wall Street
New York, New York   10005
[Attention:                         ]
           -------------------------

Dear Ladies and Gentlemen:

         In connection with our proposed sale of $ aggregate principal amount of
4.875 % First Collateral Trust Bonds, Series No. 11 due 2013 (the "Bonds") of
Public Service Company of Colorado, a Colorado corporation (the "Company"), we
confirm that:

                  (a)      the offer of the Bonds was not made to a person in
                           the United States;

                  (b)      either (i) at the time the buy order was originated,
                           the transferee was outside the United States or we
                           and any person acting on our behalf reasonably
                           believed that the transferee was outside the United
                           States or (ii) the transaction was executed in, on or
                           through the facilities of a designated off-shore
                           securities market and neither we nor any person
                           acting on our behalf knows that the transaction has
                           been pre-arranged with a buyer in the United States;

                  (c)      no directed selling efforts have been made in the
                           United States in contravention of the requirements of
                           Rule 903(b) or Rule 904(b) of Regulation S, as
                           applicable; and

                  (d)      the transaction is not part of a plan or scheme to
                           evade the registration requirements of the Securities
                           Act.

                           In addition, if the sale is made during a
Distribution Compliance Period (within the meaning of Regulation S), we confirm
that, to the best of our knowledge after due inquiry, the purchaser is not a
U.S. Person (within the meaning of Regulation S).

                           Further, if the sale is made during a Distribution
Compliance Period and the provisions of Rule 903(a)(3) or Rule 904(b)(1) of
Regulation S are applicable thereto, we confirm that such sale has been made in
accordance with the applicable provisions of Rule 903(a)(3) or Rule 904(b)(1),
as the case may be.

                                   EXHIBIT C-1
<PAGE>

                           The Company and the Trustee are entitled to rely upon
this letter and are irrevocably authorized to produce this letter or a copy
hereof to any interested party in any administrative or legal proceedings or
official inquiry with respect to the matters covered hereby. Terms used in this
certificate have the meanings set forth in Regulation S.

                                         Very truly yours,
                                         (Name of Transferor]

                                         By:
                                            ---------------------------

      Date:
           ----------------------

                                   EXHIBIT C-2

<PAGE>

                                                                      SCHEDULE A

                             SUPPLEMENTAL INDENTURES

<Table>
<Caption>
         DATE OF                                                                                 PRINCIPAL
      SUPPLEMENTAL                                                       PRINCIPAL                 AMOUNT
        INDENTURE                     SERIES OF BONDS                  AMOUNT ISSUED            OUTSTANDING
        ---------                     ---------------                  -------------            -----------
<S>                                <C>                                 <C>                      <C>
November 1, 1993                        Series No. 1                    $134,500,000            $134,500,000
January 1, 1994                    Series No. 2 due 2001                $102,667,000                None
                                            and
                                   Series No. 2 due 2024                $110,000,000            $110,000,000
September 2, 1994                           None                            None                    None
(Appointment of
Successor Trustee)
May 1, 1996                             Series No. 3                    $125,000,000            $125,000,000
November 1, 1996                        Series No. 4                    $250,000,000            $175,000,000
February 1, 1997                        Series No. 5                    $150,000,000                None
April 1, 1998                           Series No. 6                    $250,000,000            $250,000,000
August 15, 2002                         Series No. 7                    $ 48,750,000            $ 48,750,000
September 1, 2002                       Series No. 8                    $600,000,000            $600,000,000
September 15, 2002                      Series No. 9                    $530,000,000            $530,000,000
</Table>

                                  SCHEDULE A-1<PAGE>
                                                                 EXHIBIT 4(b)(4)

                             PUBLIC SERVICE COMPANY
                                   OF COLORADO

                                       TO

                      U.S. BANK TRUST NATIONAL ASSOCIATION,

                                                                      AS TRUSTEE

                              ---------------------

                         SUPPLEMENTAL INDENTURE NO. [ ]

                          Dated as of [              ]
                                       --------------

                          Supplemental to the Indenture
                           dated as of October 1, 1993

                              ---------------------

                 Establishing the Securities of Series No. [ ],
             designated First Collateral Trust Bonds, Series No. [ ]

<PAGE>

         SUPPLEMENTAL INDENTURE NO. [ ], dated as of [______________], between
PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and existing
under the laws of the State of Colorado (hereinafter sometimes called the
"Company"), and U.S. BANK TRUST NATIONAL ASSOCIATION (FORMERLY FIRST TRUST OF
NEW YORK, NATIONAL ASSOCIATION), a national banking association, as successor
trustee (hereinafter sometimes called the "Trustee") to Morgan Guaranty Trust
Company of New York under the Indenture, dated as of October 1, 1993
(hereinafter called the "Original Indenture"), as previously supplemented and as
further supplemented by this Supplemental Indenture No. [ ]. The Original
Indenture and any and all indentures and all other instruments supplemental
thereto are hereinafter sometimes collectively called the "Indenture".

                             RECITALS OF THE COMPANY

         The Original Indenture was authorized, executed and delivered by the
Company to provide for the issuance from time to time of its Securities (such
term and all other capitalized terms used herein without definition having the
meanings assigned to them in the Original Indenture), to be issued in one or
more series as contemplated therein, and to provide security for the payment of
the principal of and premium, if any, and interest, if any, on the Securities.

         The Company has heretofore executed and delivered to the Trustee the
Supplemental Indentures referred to in Schedule A hereto for the purpose of
establishing a series of bonds and appointing the successor Trustee.

         The Company desires to establish a series of Securities to be
designated "First Collateral Trust Bonds, Series No. [ ]", such series of
Securities to be hereinafter sometimes called "Series No. [ ]".

         The Company has duly authorized the execution and delivery of this
Supplemental Indenture No. [ ] to establish the Securities of Series No. [ ] and
has duly authorized the issuance of such Securities; and all acts necessary to
make this Supplemental Indenture No. [ ] a valid agreement of the Company, and
to make the Securities of Series No. [ ] valid obligations of the Company, have
been performed.

                                GRANTING CLAUSES

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE NO. [ ] WITNESSETH, that,
in consideration of the premises and of the purchase of the Securities by the
Holders thereof, and in order to secure the payment of the principal of and
premium, if any, and interest, if any, on all Securities from time to time
Outstanding and the performance of the covenants contained therein and in the
Indenture and to declare the terms and conditions on which such Securities are
secured, the Company hereby grants, bargains, sells, releases, conveys, assigns,
transfers, mortgages, pledges, sets over and confirms to the Trustee, and grants
to the Trustee a security interest in, the following:

                              GRANTING CLAUSE FIRST

         All right, title and interest of the Company, as of the date of the
         execution and delivery of this Supplemental Indenture No. [ ], in and
         to property (other than Excepted Property), real, personal and mixed
         and wherever situated, in any case used or to be used in or in
         connection with the Electric Utility Business (whether or not such use
         is the sole use of such property), including without limitation (a) all
         lands, easements, servitudes, licenses, permits, rights of way and
         other rights and interests in or relating to real property used or to
         be used in or in connection with the Electric Utility Business or
         relating to the occupancy or use of such real property, subject
         however, to the exceptions and exclusions set forth in clause (a) of
         Granting Clause First of the Original Indenture; (b) all plants,

<PAGE>

         generators, turbines, engines, boilers, fuel handling and
         transportation facilities, air and water pollution control and sewage
         and solid waste disposal facilities and other machinery and facilities
         for the generation of electric energy; (c) all switchyards, lines,
         towers, substations, transformers and other machinery and facilities
         for the transmission of electric energy; (d) all lines, poles,
         conduits, conductors, meters, regulators and other machinery and
         facilities for the distribution of electric energy; (e) all buildings,
         offices, warehouses and other structures used or to be used in or in
         connection with the Electric Utility Business; (f) all pipes, cables,
         insulators, ducts, tools, computers and other data processing and/or
         storage equipment and other equipment, apparatus and facilities used or
         to be used in or in connection with the Electric Utility Business; (g)
         any or all of the foregoing properties in the process of construction;
         and (h) all other property, of whatever kind and nature, ancillary to
         or otherwise used or to be used in conjunction with any or all of the
         foregoing or otherwise, directly or indirectly, in furtherance of the
         Electric Utility Business;

                             GRANTING CLAUSE SECOND

         Subject to the applicable exceptions permitted by Section 810(c),
         Section 1303 and Section 1305 of the Original Indenture, all property
         (other than Excepted Property) of the kind and nature described in
         Granting Clause First which may be hereafter acquired by the Company,
         it being the intention of the Company that all such property acquired
         by the Company after the date of the execution and delivery of this
         Supplemental Indenture No. [ ] shall be as fully embraced within and
         subjected to the Lien hereof as if such property were owned by the
         Company as of the date of the execution and delivery of this
         Supplemental Indenture No. [ ];

                             GRANTING CLAUSE FOURTH

         All other property of whatever kind and nature subjected or required to
         be subjected to the Lien of the Indenture by any of the provisions
         thereof;

                                EXCEPTED PROPERTY

         Expressly excepting and excluding, however, from the Lien and operation
         of the Indenture all Excepted Property of the Company, whether now
         owned or hereafter acquired;

         TO HAVE AND TO HOLD all such property, real, personal and mixed, unto
the Trustee, its successors in trust and their assigns forever;

         SUBJECT, HOWEVER, to (a) Liens existing at the date of the execution
and delivery of the Original Indenture (including, but not limited to, the Lien
of the PSCO 1939 Mortgage), (b) as to property acquired by the Company after the
date of the execution and delivery of the Original Indenture, Liens existing or
placed thereon at the time of the acquisition thereof (including, but not
limited to, the Lien of any Class A Mortgage and purchase money Liens), (c)
Retained Interests and (d) any other Permitted Liens, it being understood that,
with respect to any property which was at the date of execution and delivery of
the Original Indenture or thereafter became or hereafter becomes subject to the
Lien of any Class A Mortgage, the Lien of the Indenture shall at all times be
junior, subject and subordinate to the Lien of such Class A Mortgage;

                                       2
<PAGE>

         IN TRUST, NEVERTHELESS, for the equal and proportionate benefit and
security of the Holders from time to time of all Outstanding Securities without
any priority of any such Security over any other such Security;

         PROVIDED, HOWEVER, that the right, title and interest of the Trustee in
and to the Mortgaged Property shall cease, terminate and become void in
accordance with, and subject to the conditions set forth in, Article Nine of the
Original Indenture, and if, thereafter, the principal of and premium, if any,
and interest, if any, on the Securities shall have been paid to the Holders
thereof, or shall have been paid to the Company pursuant to Section 603 of the
Original Indenture, then and in that case the Indenture shall terminate, and the
Trustee shall execute and deliver to the Company such instruments as the Company
shall require to evidence such termination; otherwise the Indenture, and the
estate and rights thereby granted shall be and remain in full force and effect;
and

         THE PARTIES HEREBY FURTHER COVENANT AND AGREE as follows:

                                   ARTICLE ONE

                          SECURITIES OF SERIES NO. [ ]

         There are hereby established the Securities of Series No. [ ], which
shall have the terms and characteristics set forth below (the lettered
subdivisions set forth below corresponding to the lettered subdivisions of
Section 301 of the Original Indenture):

         (a) the title of the Securities of such series shall be "First
         Collateral Trust Bonds, Series No. [ ]"; provided, however, that, at
         any time after the PSCO 1939 Mortgage shall have been satisfied and
         discharged, the Company shall have the right, without any consent or
         other action by the Holders of such Securities, to change such title in
         such manner as shall be deemed by the Company to be appropriate to
         reflect such satisfaction and discharge, such change to be evidenced in
         an Officer's Certificate;

         (b) the Securities of Series No. [ ] shall be initially authenticated
         and delivered in the aggregate principal amount of [up to]
         $[___________];

         (c) interest on the Securities of Series No. [ ] shall be payable to
         the Persons in whose names such Securities are registered at the close
         of business on the Regular Record Date for such interest, except as
         otherwise expressly provided in the form of such Securities attached as
         Exhibit A hereto;

         (d) the principal of the Securities of Series No. [ ] shall be payable
         on [ ], the Stated Maturity.

         (e) the Securities of Series No. [ ] shall bear interest at a rate of
         [ ]% per annum; interest shall accrue on the Securities of Series No.
         [ ] from [______________], or the most recent date to which interest
         has been paid or duly provided for; the Interest Payment Dates for such
         Securities shall be [ ] and [ ] in each year, commencing
         [______________], and the Regular Record Dates with respect to the
         Interest Payment Dates for such Securities shall be [ ] and [ ] in each
         year, respectively (whether or not a Business Day);

                                       3
<PAGE>

         (f) the Corporate Trust Office of U.S. Bank Trust National Association
         in New York, New York shall be the place at which (i) the principal
         of[, premium, if any,] and interest, if any, on the Securities of
         Series No. [ ] shall be payable, (ii) registration of transfer of such
         Securities may be effected, (iii) exchanges of such Securities may be
         effected and (iv) notices and demands to or upon the Company in respect
         of such Securities and the Indenture may be served; and U.S. Bank Trust
         National Association shall be the Security Registrar for such
         Securities; provided, however, that the Company reserves the right to
         change, by one or more Officer's Certificates, any such place or the
         Security Registrar; and provided, further, that the Company reserves
         the right to designate, by one or more Officer's Certificates, its
         principal office in Denver, Colorado as any such place or itself as the
         Security Registrar;

         (g) the Securities of Series No. [ ] [shall not be redeemable prior to
         [____________]. On and after that date, the Securities of Series No.
         [ ]]; [shall be redeemable in whole or in part, at the option of the
         Company, during the period, at [__________________].

         (h) not applicable;

         (i) not applicable;

         (j) not applicable;

         (k) not applicable;

         (l) not applicable;

         (m) not applicable;

         (n) not applicable;

         (o) not applicable;

         (p) not applicable;

         (q) the Securities of Series No. [ ] are to be initially registered in
         the name of Cede & Co., as nominee for The Depository Trust Company
         (the "Depositary"). Such Securities shall not be transferable or
         exchangeable, nor shall any purported transfer be registered, except as
         follows:

                  (i)      such Securities may be transferred in whole, and
                           appropriate registration of transfer effected, if
                           such transfer is by such nominee to the Depositary,
                           or by the Depositary to another nominee thereof, or
                           by any nominee of the Depositary to any other nominee
                           thereof, or by the Depositary or any nominee thereof
                           to any successor securities depositary or any nominee
                           thereof; and

                  (ii)     such Securities may be exchanged for definitive
                           Securities registered in the respective names of the
                           beneficial holders thereof, and thereafter shall be
                           transferable without restriction, if:

                           (A)      the Depositary, or any successor securities
                                    depositary, shall have notified the Company
                                    and the Trustee that it is unwilling or
                                    unable to continue to act as securities
                                    depositary with respect to such Securities
                                    or the Depository has ceased to be a
                                    clearing agency registered under the

                                       4
<PAGE>

                                    Securities Exchange Act of 1934, as amended,
                                    and the Trustee shall not have been notified
                                    by the Company within ninety (90) days of
                                    the identity of a successor securities
                                    depositary with respect to such Securities;

                           (B)      the Company shall have delivered to the
                                    Trustee a Company Order to the effect that
                                    such Securities shall be so exchangeable on
                                    and after a date specified therein; or

                           (C)      (1) an Event of Default shall have occurred
                                    and be continuing, (2) the Trustee shall
                                    have given notice of such Event of Default
                                    pursuant to Section 1102 of the Original
                                    Indenture and (3) there shall have been
                                    delivered to the Company and the Trustee an
                                    Opinion of Counsel to the effect that the
                                    interests of the beneficial owners of such
                                    Securities in respect thereof will be
                                    materially impaired unless such owners
                                    become Holders of definitive Securities.;

         (r) not applicable;

         (s) no service charge shall be made for the registration of transfer or
         exchange of the Securities of Series No. [ ]; provided, however, that
         the Company may require payment of a sum sufficient to cover any tax or
         other governmental charge payable in connection with the exchange or
         transfer;

         (t) not applicable;

         (u) (i) If the Company shall have caused the Company's indebtedness in
             respect of any Securities of Series No. [ ] to have been satisfied
             and discharged prior to the Maturity of such Securities, as
             provided in Section 901 of the Original Indenture, the Company
             shall, promptly after the date of such satisfaction and discharge,
             give a notice to each Person who was a Holder of any of such
             Securities on such date stating (A)(1) the aggregate principal
             amount of such Securities and (2) the aggregate amount of any money
             (other than amounts, if any, deposited in respect of accrued
             interest on such Securities) and the aggregate principal amount of,
             the rate or rates of interest on, and the aggregate fair market
             value of, any Eligible Obligations deposited pursuant to Section
             901 of the Original Indenture with respect to such Securities and
             (B) that the Company will provide (and the Company shall promptly
             so provide) to such Person, or any beneficial owner of such
             Securities holding through such Person (upon written request to the
             Company sent to an address specified in such notice), such other
             information as such Person or beneficial owner, as the case may be,
             reasonably may request in order to enable it to determine the
             federal income tax consequences to it resulting from the
             satisfaction and discharge of the Company's indebtedness in respect
             of such Securities. Thereafter, the Company shall, within
             forty-five (45) days after the end of each calendar year, give to
             each Person who at any time during such calendar year was a Holder
             of such Securities a notice containing (X) such information as may
             be necessary to enable such Person to report its income, gain or
             loss for federal income tax purposes with respect to such
             Securities or the assets held on deposit in respect thereof during
             such calendar year or the portion thereof during which such Person
             was a Holder of such Securities, as the case may be (such
             information to be set forth for such calendar year as a whole and
             for each month during such year) and (Y) a statement to the effect
             that the Company will provide (and the Company shall promptly so
             provide) to such Person, or any beneficial owner of

                                       5
<PAGE>

             such Securities holding through such Person (upon written request
             to the Company sent to an address specified in such notice), such
             other information as such Person or beneficial owner, as the case
             may be, reasonably may request in order to enable it to determine
             its income, gain or loss for federal income tax purposes with
             respect to such Securities or such assets for such year or portion
             thereof, as the case may be. The obligation of the Company to
             provide or cause to be provided information for purposes of income
             tax reporting by any Person as described in the first two sentences
             of this paragraph shall be deemed to have been satisfied to the
             extent that the Company has provided or caused to be provided
             substantially comparable information pursuant to any requirements
             of the Internal Revenue Code of 1986, as amended from time to time
             (the "Code") and United States Treasury regulations thereunder.

             (ii) Notwithstanding the provisions of subparagraph (i) above, the
             Company shall not be required to give any notice specified in such
             subparagraph or to otherwise furnish any of the information
             contemplated therein if the Company shall have delivered to the
             Trustee an Opinion of Counsel to the effect that the Holders of
             such Securities will not recognize income, gain or loss for federal
             income tax purposes as a result of the satisfaction and discharge
             of the Company's indebtedness in respect of such Securities and
             such Holders will be subject to federal income taxation on the same
             amounts and in the same manner and at the same times as if such
             satisfaction and discharge had not occurred.

             (iii) Anything in this clause (u) to the contrary notwithstanding,
             the Company shall not be required to give any notice specified in
             subparagraph (i) or to otherwise furnish the information
             contemplated therein or to deliver any Opinion of Counsel
             contemplated by subparagraph (ii) if the Company shall have caused
             Securities of Series No. [ ] to be deemed to have been paid for
             purposes of the Indenture, as provided in Section 901 of the
             Original Indenture, but shall not have effected the satisfaction
             and discharge of its indebtedness in respect of such Securities
             pursuant to such Section.

         (v) The Securities of Series No. [ ] shall be substantially in the form
         attached hereto as Exhibit A and shall have such further terms as are
         set forth in such form.

                                   ARTICLE TWO

                            MISCELLANEOUS PROVISIONS

         This Supplemental Indenture No. [ ] is a supplement to the Original
Indenture. As previously supplemented and further supplemented by this
Supplemental Indenture No. [ ], the Original Indenture is in all respects
ratified, approved and confirmed, and the Original Indenture, all previous
supplements thereto and this Supplemental Indenture No. [ ] shall together
constitute one and the same instrument.

                                       6
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture No. [ ] to be duly executed as of the day and year first above
written.

                                     PUBLIC SERVICE COMPANY OF COLORADO

                                     By:
                                            ------------------------------------

                                            Name:
                                            Title:

STATE OF [__________]       )
                            ) ss.:
COUNTY OF [__________]      )

         On the [_____] day of [________, ______], before me personally came
[__________] to me known, who, being by me duly sworn, did depose and say that
he is a [__________] of Public Service Company of Colorado, one of the
corporations described in and which executed the foregoing instrument; and that
he signed his name thereto by authority of the Board of Directors of said
corporation.

                                      ------------------------------------------
                                      Name:
                                      Notary Public, State of [          ]
                                                               ----------
                                      Commission Expires:

                                       7
<PAGE>

                                     U.S. BANK TRUST NATIONAL ASSOCIATION,
                                                            Trustee

                                     By:
                                        ----------------------------------------

                                        Name:
                                        Title:

STATE OF [__________]            )
                                 ) ss.:
COUNTY OF [__________]           )

         On the [_____] day of [__________, ____], before me personally came
[__________], to me known, who, being by me duly sworn, did depose and say that
he is an [__________] of U.S. Bank Trust National Association, the banking
association described in and which executed the foregoing instrument; and that
he signed his name thereto by authority of the Board of Directors of said
banking association.

                                      ------------------------------------------
                                      Name:
                                      Notary Public, State of [          ]
                                                               ----------
                                      Commission Expires:

                                       8
<PAGE>

                                                                       EXHIBIT A

                                FORM OF SECURITY

                   (See legend at the end of this Security for
                            restrictions on transfer)

                       PUBLIC SERVICE COMPANY OF COLORADO
                   First Collateral Trust Bond, Series No. [ ]

       Original Interest Accrual Date:           [                          ]
                                                  --------------------------
                        Interest Rate:           [                          ]
                                                  --------------------------
                      Stated Maturity:           [                          ]
                                                  --------------------------
               Interest Payment Dates:           [            ] and [       ]
                                                  -------------       ------
                 Regular Record Dates:           [            ] and [       ]
                                                  -------------       ------

                    This Security is not a Discount Security
              within the meaning of the within-mentioned Indenture

                    -----------------------------------------

Principal Amount                                                  Registered No.
$                                                                 CUSIP

         PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and
existing under the laws of the State of Colorado (herein called the "Company,"
which term includes any successor corporation under the Indenture referred to
below), for value received, hereby promises to pay to [_____
____________________________________________________], or registered assigns,
the principal sum of Dollars on the Stated Maturity specified above, and to pay
interest thereon from the Original Interest Accrual Date specified above or from
the most recent Interest Payment Date to which interest has been paid or duly
provided for, semi-annually in arrears on the Interest Payment Dates specified
above in each year, commencing [______________], and at Maturity, at the
Interest Rate per annum specified above, until the principal hereof is paid or
duly provided for. The interest so payable, and paid or duly provided for, on
any Interest Payment Date shall, as provided in such Indenture, be paid to the
Person in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on the Regular Record Date specified above
(whether or not a Business Day) next preceding such Interest Payment Date.
Notwithstanding the foregoing, interest payable at Maturity shall be paid to the
Person to whom principal shall be paid. Except as otherwise provided in said
Indenture, any such interest not so paid or duly provided for shall forthwith
cease to be payable to the Holder on such Regular Record Date and may either be
paid to the Person in whose name this Security (or one or more Predecessor
Securities) is registered at the close of business on a Special Record Date for
the payment of such Defaulted Interest to be fixed by the Trustee, notice of
which shall be given to Holders of Securities of this series not less than 15
days prior to such Special Record Date, or be paid in such other manner as
permitted by the Indenture.

                                      A-1
<PAGE>

         Payment of the principal of this Security and interest hereon at
Maturity shall be made upon presentation of this Security at the Corporate Trust
Office of U.S. Bank Trust National Association, in New York, New York or at such
other office or agency as may be designated for such purpose by the Company from
time to time. Payment of interest on this Security (other than interest at
Maturity) shall be made by check mailed to the address of the Person entitled
thereto as such address shall appear in the Security Register, except that if
such Person shall be a securities depositary, such payment may be made by such
other means in lieu of check as shall be agreed upon by the Company, the Trustee
and such Person. Payment of the principal of and interest on this Security, as
aforesaid, shall be made in such coin or currency of the United States of
America as at the time of payment shall be legal tender for the payment of
public and private debts.

         This Security is one of a duly authorized issue of securities of the
Company (herein called the "Securities"), issued and issuable in one or more
series under and equally secured by an Indenture, dated as of October 1, 1993
(such Indenture as originally executed and delivered and as supplemented or
amended from time to time thereafter, together with any constituent instruments
establishing the terms of particular Securities, being herein called the
"Indenture"), between the Company and U.S. Bank Trust National Association
(formerly First Trust of New York, National Association) as successor trustee
(herein called the "Trustee," which term includes any successor trustee under
the Indenture), to which Indenture and all indentures supplemental thereto
reference is hereby made for a description of the property mortgaged, pledged
and held in trust, the nature and extent of the security and the respective
rights, limitations of rights, duties and immunities of the Company, the Trustee
and the Holders of the Securities thereunder and of the terms and conditions
upon which the Securities are, and are to be, authenticated and delivered and
secured. The acceptance of this Security shall be deemed to constitute the
consent and agreement by the Holder hereof to all of the terms and provisions of
the Indenture. This Security is one of the series designated above.

         If any Interest Payment Date or the Stated Maturity shall not be a
Business Day (as hereinafter defined), payment of the amounts due on this
Security on such date may be made on the next succeeding Business Day; and, if
such payment is made or duly provided for on such Business Day, no interest
shall accrue on such amounts for the period from and after such Interest Payment
Date or Stated Maturity, as the case may be, to such Business Day.

         [This Security is not subject to redemption prior to the Stated
Maturity hereof.]

         [This Security is subject to redemption at any time on or after
___________, as a whole at any time or from time to time in part, at the option
of the Company, at a redemption price equal to [__________].

         [Notwithstanding the foregoing, the Company may not, prior to
__________, redeem this Security as contemplated above as a part of, or in
anticipation of, any refunding operation by the application, directly or
indirectly, of moneys borrowed having an effective interest cost to the Company
(calculated in accordance with generally accepted financial practice) less than
the effective interest cost to the Company (similarly calculated) of this
Security.]

         [Insert provisions, if any, for redemption pursuant to a sinking fund
or analogous provision or at the option of the holder.]

         [Notice of redemption shall be given by mail to the Holder of this
Security, not less than 30 days nor more than 60 days prior to the date fixed
for redemption, all as provided in the Indenture. As provided in the Indenture,
notice of redemption at the election of the Company as aforesaid may state that
such redemption shall be conditional upon the receipt by the Paying Agent or
Agents for this Security, on or prior to the date fixed for such redemption, of
money sufficient to pay the principal of and premium, if

                                      A-2
<PAGE>

any, and interest, on this Security; a notice of redemption so conditioned shall
be of no force or effect if such money is not so received and, in such event,
the Company shall not be required to redeem this Security].

         [In the event of redemption of this Security in part only, a new
Security or Securities of this series, of like tenor, for the unredeemed portion
hereof and otherwise having the same terms as this Security will be issued in
the name of the Holder hereof upon the cancellation hereof.]

         If an Event of Default shall occur and be continuing, the principal of
this Security may be declared due and payable in the manner and with the effect
provided in the Indenture.

         The Indenture permits, with certain exceptions as therein provided, the
Trustee to enter into one or more supplemental indentures for the purpose of
adding any provisions to, or changing in any manner or eliminating any of the
provisions of, the Indenture with the consent of the Holders of not less than a
majority in aggregate principal amount of the Securities of all series then
Outstanding under the Indenture, considered as one class; provided, however,
that if there shall be Securities of more than one series Outstanding under the
Indenture and if a proposed supplemental indenture shall directly affect the
rights of the Holders of Securities of one or more, but less than all, of such
series, then the consent only of the Holders of a majority in aggregate
principal amount of the Outstanding Securities of all series so directly
affected, considered as one class, shall be required; and provided, further,
that if the Securities of any series shall have been issued in more than one
Tranche and if the proposed supplemental indenture shall directly affect the
rights of the Holders of Securities of one or more, but less than all, of such
Tranches, then the consent only of the Holders of a majority in aggregate
principal amount of the Outstanding Securities of all Tranches so directly
affected, considered as one class, shall be required; and provided, further,
that the Indenture permits the Trustee to enter into one or more supplemental
indentures for limited purposes without the consent of any Holders of
Securities. The Indenture also contains provisions permitting the Holders of a
majority in principal amount of the Securities then Outstanding, on behalf of
the Holders of all Securities, to waive compliance by the Company with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the Holder of this Security
shall be conclusive and binding upon such Holder and upon all future Holders of
this Security and of any Security issued upon the registration of transfer
hereof or in exchange therefor or in lieu hereof, whether or not notation of
such consent or waiver is made upon this Security.

         As provided in the Indenture and subject to certain limitations therein
set forth, this Security or any portion of the principal amount hereof will be
deemed to have been paid for all purposes of the Indenture and to be no longer
Outstanding thereunder, and, at the election of the Company, the Company's
entire indebtedness in respect thereof will be satisfied and discharged, if
there has been irrevocably deposited with the Trustee or any Paying Agent (other
than the Company), in trust, money in an amount which will be sufficient and/or
Eligible Obligations, the principal of and interest on which when due, without
regard to any reinvestment thereof, will provide moneys which, together with
moneys so deposited, will be sufficient, to pay when due the principal of and
interest on this Security when due.

         As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office of U.S. Bank Trust National Association, in New York, New York or such
other office or agency as may be designated by the Company from time to time,
duly endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Company and the Security Registrar duly executed by, the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Securities of this series of authorized denominations and of like tenor
and aggregate principal amount, will be issued to the designated transferee or
transferees.

                                      A-3
<PAGE>

         The Securities of this series are issuable only as registered
Securities, without coupons, and in denominations of $1,000 and integral
multiples thereof. As provided in the Indenture and subject to certain
limitations therein set forth, Securities of this series are exchangeable for a
like aggregate principal amount of Securities of the same series, of any
authorized denominations, as requested by the Holder surrendering the same, and
of like tenor upon surrender of the Security or Securities to be exchanged at
the office of U.S. Bank Trust National Association, in New York, New York or
such other office or agency as may be designated by the Company from time to
time.

         [The Company shall not be required to execute or provide for the
registration of transfer of or the exchange of (a) Securities of this series
during a period of 15 day immediately preceding the date notice is given
identifying the serial numbers of the Securities of this series called for
redemption or (b) any Security so selected for redemption in whole or in part,
except the unredeemed portion of any Security being redeemed in part.]

         No service charge shall be made for any such registration of transfer
or exchange, but the Company may require payment of a sum sufficient to cover
any tax or other governmental charge payable in connection therewith.

         Prior to due presentment of this Security for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name this Security is registered as the absolute owner
hereof for all purposes, whether or not this Security be overdue, and neither
the Company, the Trustee nor any such agent shall be affected by notice to the
contrary.

         The Indenture and the Securities shall be governed by and construed in
accordance with the laws of the State of New York.

         As used herein "Business Day" means any day, other than a Saturday or
Sunday, which is not a day on which banking institutions or trust companies in
The City of New York, New York or other city in which is located any office or
agency maintained for the payment of principal or interest on this Security, are
authorized or required by law, regulation or executive order to remain closed.
All other terms used in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.

         As provided in the Indenture, no recourse shall be had for the payment
of the principal of[, premium, if any] or interest on any Securities, or any
part thereof, or for any claim based thereon or otherwise in respect thereof, or
of the indebtedness represented thereby, or upon any obligation, covenant or
agreement under the Indenture, against, and no personal liability whatsoever
shall attach to, or be incurred by, any incorporator, shareholder, officer or
director, as such, past, present or future of the Company or of any predecessor
or successor corporation (either directly or through the Company or a
predecessor or successor corporation), whether by virtue of any constitutional
provision, statute or rule of law, or by the enforcement of any assessment or
penalty or otherwise; it being expressly agreed and understood that the
Indenture and all the Securities are solely corporate obligations and that any
such personal liability is hereby expressly waived and released as a condition
of, and as part of the consideration for, the execution of the Indenture and the
issuance of the Securities.

         Unless the certificate of authentication hereon has been executed by
the Trustee or an Authenticating Agent by manual signature, this Security shall
not be entitled to any benefit under the Indenture or be valid or obligatory for
any purpose.

                                      A-4
<PAGE>
IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed
and its corporate seal to be hereunto affixed and attested.

                                      PUBLIC SERVICE COMPANY OF COLORADO

                                      By:
                                         ---------------------------------------
                                               [Title]

Attest:
       ----------------------------
              [Title]

                          CERTIFICATE OF AUTHENTICATION

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

Dated:
      -----------------------------

            U.S. BANK TRUST              OR             U.S. BANK TRUST
         NATIONAL ASSOCIATION,                       NATIONAL ASSOCIATION,
              as Trustee                                  as Trustee

By:                                             By:
   --------------------------------                -----------------------------
         Authorized Officer                         as Authenticating Agent

                                                By:
                                                   -----------------------------
                                                     Authorized Officer

         UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF
THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION ("DTC"), TO THE COMPANY 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 OWNER
HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

         THIS SECURITY MAY NOT BE TRANSFERRED OR EXCHANGED, NOR MAY ANY
PURPORTED TRANSFER BE REGISTERED, EXCEPT (i) THIS SECURITY MAY BE TRANSFERRED IN
WHOLE, AND APPROPRIATE REGISTRATION OF TRANSFER EFFECTED, IF SUCH TRANSFER IS BY
CEDE & CO., AS NOMINEE FOR THE DEPOSITORY TRUST COMPANY (THE "DEPOSITARY"), TO
THE DEPOSITARY, OR BY THE DEPOSITARY TO ANOTHER NOMINEE THEREOF, OR BY ANY
NOMINEE OF THE DEPOSITARY TO ANY OTHER NOMINEE THEREOF, OR BY THE DEPOSITARY OR
ANY NOMINEE THEREOF TO ANY SUCCESSOR SECURITIES DEPOSITARY OR ANY NOMINEE
THEREOF; AND (II) THIS SECURITY MAY BE EXCHANGED FOR DEFINITIVE SECURITIES
REGISTERED IN THE RESPECTIVE NAMES OF THE BENEFICIAL HOLDERS HEREOF, AND
THEREAFTER SHALL BE TRANSFERABLE WITHOUT RESTRICTIONS IF: (A) THE DEPOSITARY, OR
ANY SUCCESSOR SECURITIES DEPOSITARY, SHALL HAVE NOTIFIED THE COMPANY AND THE
TRUSTEE THAT IT IS UNWILLING OR UNABLE TO CONTINUE TO ACT AS SECURITIES
DEPOSITARY WITH RESPECT TO THE SECURITIES AND THE TRUSTEE SHALL NOT HAVE BEEN
NOTIFIED BY THE COMPANY WITHIN NINETY (90) DAYS OF THE IDENTITY OF A SUCCESSOR
SECURITIES DEPOSITARY WITH RESPECT TO THE SECURITIES; (B) THE COMPANY SHALL HAVE
DELIVERED TO THE TRUSTEE A

                                      A-5
<PAGE>

COMPANY ORDER TO THE EFFECT THAT THE SECURITIES SHALL BE SO EXCHANGEABLE ON AND
AFTER A DATE SPECIFIED THEREIN; OR (C)(1) AN EVENT OF DEFAULT SHALL HAVE
OCCURRED AND BE CONTINUING, (2) THE TRUSTEE SHALL HAVE GIVEN NOTICE OF SUCH
EVENT OF DEFAULT PURSUANT TO SECTION 1102 OF THE INDENTURE AND (3) THERE SHALL
HAVE BEEN DELIVERED TO THE COMPANY AND THE TRUSTEE AN OPINION OF COUNSEL TO THE
EFFECT THAT THE INTERESTS OF THE BENEFICIAL OWNERS OF THE SECURITIES IN RESPECT
THEREOF WILL BE MATERIALLY IMPAIRED UNLESS SUCH OWNERS BECOME HOLDERS OF
DEFINITIVE SECURITIES.

                            ------------------------

                                      A-6
<PAGE>

         FOR VALUE RECEIVED the undersigned hereby sells, assigns and transfers
unto

--------------------------------------------------------------------------------

     [please insert social security or other identifying number of assignee]

--------------------------------------------------------------------------------
            [please print or typewrite name and address of assignee]

--------------------------------------------------------------------------------

the within Security of PUBLIC SERVICE COMPANY OF COLORADO and does hereby
irrevocably constitute and appoint __________________________________ ,
Attorney, to transfer said Security on the books of the within-mentioned
Company, with full power of substitution in the premises.

Dated:
      ---------------------------

             ------------------------------------------------------

         Notice: The signature to this assignment must correspond with the name
         as written upon the face of the Security in every particular without
         alteration or enlargement or any change whatsoever.

                                      A-7
<PAGE>

                            OPTION TO ELECT REPAYMENT

         The undersigned hereby irrevocably request(s) and instruct(s) the
Company to repay this Note (or portion hereof specified below) pursuant to its
terms at a price equal to 100% of the principal amount to be repaid, together
with unpaid interest accrued hereon to the Repayment Date, to the undersigned,
at _____________________________________________________________________________
(Please print or typewrite name and address of the undersigned).

         For this Note to be repaid, the Trustee must receive at its Corporate
Trust Office in New York, New York not more than 60 nor less than 30 calendar
days prior to the Repayment Date, this Note with this "Option to Elect
Repayment" form duly completed.

         If less than the entire principal amount of this Note is to be repaid,
specify the portion hereof (which shall be increments of $1,000 (provided that
any remaining principal amount hereof shall be at least $100,000)) which the
Holder elects to have repaid and specify the denomination or denominations
(which shall be a minimum of $100,000) of the Notes to be issued to the Holder
for the portion of this Note not being repaid (in the absence of any such
specification, one such Note will be issued for the portion not being repaid).

         Principal Amount to be Repaid:  $
                                          -------------------------------

         Date:
               -----------------------------

         NOTICE: The signature(s) on this Option to Elect Repayment must
correspond with the name(s) as written upon the face of this Note in every
particular, without alteration or enlargement or any change whatsoever.

                                      A-8
<PAGE>

                                                                      SCHEDULE A

                             SUPPLEMENTAL INDENTURES

<Table>
<Caption>
        DATE OF                                                                                  PRINCIPAL
      SUPPLEMENTAL                                                       PRINCIPAL                 AMOUNT
       INDENTURE                      SERIES OF BONDS                  AMOUNT ISSUED            OUTSTANDING
      ------------                    ---------------                  -------------            ------------
<S>                                <C>                                 <C>                      <C>
November 1, 1993                        Series No. 1                    $134,500,000            $134,500,000
January 1, 1994                    Series No. 2 due 2001                $102,667,000                None
                                            and
                                   Series No. 2 due 2024                $110,000,000            $110,000,000
September 2, 1994                           None                            None                    None
(Appointment of
Successor Trustee)
May 1, 1996                             Series No. 3                    $125,000,000            $125,000,000
November 1, 1996                        Series No. 4                    $250,000,000            $175,000,000
February 1, 1997                        Series No. 5                    $150,000,000                None
April 1, 1998                           Series No. 6                    $250,000,000            $250,000,000
August 15, 2002                         Series No. 7                    $ 48,750,000            $ 48,750,000
September 1, 2002                       Series No. 8                    $600,000,000            $600,000,000
September 15, 2002                      Series No. 9                    $530,000,000            $530,000,000
March 1, 2003                          Series No. 11                    $250,000,000            $250,000,000
</Table>

                                      A-9

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