<PAGE>
                                                                    EXHIBIT 4.04

                             PUBLIC SERVICE COMPANY
                                   OF COLORADO

                                       TO


                      U.S. BANK TRUST NATIONAL ASSOCIATION,

                                                AS TRUSTEE


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


                          SUPPLEMENTAL INDENTURE NO. 10

                         Dated as of September 15, 2002


                          Supplemental to the Indenture
                           dated as of October 1, 1993

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


                  Establishing the Securities of Series No. 9,
              designated First Collateral Trust Bonds, Series No. 9
                       (Bank of America Collateral Bonds)



<PAGE>




         SUPPLEMENTAL INDENTURE NO. 10, dated as of September 15, 2002, 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. 10. 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 has heretofore entered into a Second Amended and Restated
364-Day Credit Agreement (the "Credit Agreement"), dated as of June 28, 2002,
with Bank of America, N.A., as Administrative Agent (the "Administrative Agent")
and the several financial institutions and other persons from time to time party
thereto (collectively, the "Lenders"), pursuant to which the Lenders have agreed
to make advances and grant certain other financial accommodations to the Company
up to an aggregate amount of Five Hundred Thirty Million dollars ($530,000,000)
(the "Loans"). The Credit Agreement was amended by that certain First Amendment
to Second Amended and Restated 364-Day Credit Agreement, dated as of September
6, 2002 (the "First Amendment"), between the Company and the Administrative
Agent, pursuant to which certain provisions in the Credit Agreement were
modified, including, without limitation, the addition of a covenant requiring
the Company to cause the principal amount of the Company's obligations under the
Credit Agreement to be ratably secured with all indebtedness of the Company
under the Indenture, as a condition to, and as consideration for, the obligation
of the Lenders to continue to make the Loans in accordance with the terms of the
Credit Agreement.

         Pursuant to its obligations under the First Amendment, the Company now
desires to establish a series of Securities to be designated "First Collateral
Trust Bonds, Series No. 9 (Bank of America Collateral Bonds)", such series of
Securities to be hereinafter sometimes called "Series No. 9".

         The Company has duly authorized the execution and delivery of this
Supplemental Indenture No. 10 to establish the Securities of Series No. 9 and
has duly authorized the issuance of such Securities; and all acts necessary to
make this Supplemental Indenture No. 10 a valid agreement of the Company, and to
make the Securities of Series No. 9 valid obligations of the Company, have been
performed.

                                GRANTING CLAUSES

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE NO. 10 WITNESSETH, that, in
consideration of the premises, including, without limitation, the consent of the
Lenders to continue to make Loans available to the Company in accordance with
the terms of the Credit Agreement, and in


<PAGE>




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. 10, 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,
         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. 10 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. 10;

                             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;

                                       2

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                                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;

         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. 9

         There are hereby established the Securities of Series No. 9. The
Securities of Series No. 9 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. 9 (Bank of America Collateral
         Bonds)"; 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;

                                       3

<PAGE>




         (b) the Securities of Series No. 9 shall be initially authenticated and
         delivered in the aggregate principal amount of $530,000,000;

         (c) not applicable;

         (d) the principal of the Securities of Series No. 9 shall be payable on
         June 27, 2003, the Stated Maturity.

         (e) the Securities of Series No. 9 shall not bear interest;

         (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.
         9 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. 9 shall not be redeemable prior to
         maturity, other than as set forth in the Indenture;

         (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. 9 are to be registered in the name of
         Bank of America, N.A., as Administrative Agent. Such Securities shall
         not be transferable, nor shall any purported transfer be registered
         except to a successor to the Administrative Agent under the Credit
         Agreement upon delivery to the Trustee of a Company Request requesting
         such transfer.

         (r) not applicable;

                                       4

<PAGE>




         (s) no service charge shall be made for the transfer or exchange of the
         Securities of Series No. 9; 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 transfer or
         exchange;

         (t) not applicable;

         (u)      (i) If the Company shall have caused the Company's
                  indebtedness in respect of any Securities of Series No. 9 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 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

                                       5

<PAGE>



                  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. 9 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) If the Company terminates or reduces the aggregate amount of
         unutilized commitments of the Lenders to provide advances under the
         Credit Agreement pursuant to Section 2.04 thereof, such termination or
         reduction shall, to the extent thereof, be deemed to satisfy and
         discharge the obligation of the Company, if any, to make payment of
         principal on the Securities of Series No. 9. Upon payment of the
         Company's obligations under the Credit Agreement in full, termination
         of the Credit Agreement and termination of all commitments and other
         obligations of the Administrative Agent and the Lenders to the Company,
         the aggregate amount of principal of the Securities of Series No. 9
         shall be deemed satisfied and discharged.

                  On the date which is thirty (30) days after the Maturity of
         the Securities of Series No. 9, the Trustee may conclusively presume
         that the obligation of the Company to pay principal on the Securities
         of Series No. 9 as the same shall have become due and payable shall
         have been fully satisfied and discharged unless and until the Trustee
         shall have received a written notice prior to such date from the Holder
         hereof stating that the principal of Securities of Series No. 9 has
         become due and payable and specifying the amount of funds required to
         make such payment.

                  Notwithstanding anything to the contrary contained herein, the
         aggregate amount of principal actually due on the Securities of Series
         No. 9 shall not exceed the aggregate amount of the obligations of the
         Company under the Credit Agreement.

         (w) The Securities of Series No. 9 shall be subject to certain voting
         restrictions set forth in the Issuance Agreement to be entered into
         between the Company and Bank of America, N.A., as Administrative Agent.
         A copy of the Issuance Agreement will be on file at the office of the
         Trustee and will be available upon request.

         (x) The Securities of Series No. 9 shall be substantially in the form
         attached hereto as Exhibit A and shall have such further terms as are
         set forth in such form.

                                       6

<PAGE>




                                   ARTICLE TWO

                            MISCELLANEOUS PROVISIONS

         (a) This Supplemental Indenture No. 10 is a supplement to the Original
         Indenture. As previously supplemented and further supplemented by this
         Supplemental Indenture No. 10, the Original Indenture is in all
         respects ratified, approved and confirmed, and the Original Indenture,
         all previous supplements thereto and this Supplemental Indenture No. 10
         shall together constitute one and the same instrument.

         (b) This Securities of Series No. 9 have been issued by the Company to
         the Administrative Agent to (i) secure the payment of the Company's
         obligations to make payments to any person under the Credit Agreement
         and (ii) provide to such persons the benefits of the security provided
         for this Security pursuant to the Indenture.


                                       7


<PAGE>




                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture No. 10 to be duly executed as of the day and year first
above written.



                                PUBLIC SERVICE COMPANY OF COLORADO



                                  By:    /s/ Paul E. Pender
                                         ---------------------------------------
                                         Name:      Paul E. Pender
                                         Title:     Vice President and Treasurer




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

         On the 20th day of September, 2002, before me personally came Paul E.
Pender 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/ Sharon M. Quellhorst
                                       -----------------------------------------
                                       Name: Sharon M. Quellhorst
                                       Notary Public, State of Minnesota

                                       Commission Expires:  January 31, 2005

                                       8
<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 20th day of September, 2002, 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/ Doris Ware
                                         --------------------------------------
                                         Name:  Doris Ware
                                         Notary Public, State of New York


                                         Commission Expires: November 9, 2005

                                       9
<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. 9 (Bank of America Collateral Bonds)



                        Issue Date:          [September __], 2002
                   Stated Maturity:          June 27, 2003



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


Principal Amount                                           Registered No. 1
$530,000,000


         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 BANK OF AMERICA, N.A., as
Administrative Agent, or registered assigns, the principal sum of Five Hundred
Thirty Million Dollars on the Stated Maturity specified above. This Security
shall not bear interest.

         Payment of the principal of this Security 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 the principal of 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

                                  EXHIBIT A-1

<PAGE>


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.

         This Security has been issued pursuant to the requirements of, and as a
condition to, and as consideration for, the obligations of the Lenders to
continue to make the Loans under, and in accordance with the terms of, that
certain Second Amended and Restated 364-Day Credit Agreement (the "Credit
Agreement"), dated as of June 28, 2002, among the Company, Bank of America,
N.A., as Administrative Agent (the "Administrative Agent") and the several
financial institutions and other persons from time to time party thereto
(collectively, the "Lenders"), as amended by the First Amendment to Second
Amended and Restated 364-Day Credit Agreement, dated as of September 6, 2002,
between the Company and the Administrative Agent.

         If the Company terminates or reduces the aggregate amount of unutilized
commitments of the Lenders to provide advances under the Credit Agreement
pursuant to Section 2.04 thereof, such termination or reduction shall, to the
extent thereof, be deemed to satisfy and discharge the obligation of the
Company, if any, to make the payment of principal on the Securities of Series
No. 9. Upon payment of the Company's obligations under the Credit Agreement in
full, termination of the Credit Agreement and termination of all commitments and
other obligations of the Administrative Agent and the Lenders to the Company,
the aggregate amount of principal of the Securities of Series No. 9 shall be
deemed satisfied and discharged.

         On the date which is thirty (30) days after the Maturity of the
Securities of Series No. 9, the Trustee may conclusively presume that the
obligation of the Company to pay principal on the Securities of Series No. 9 as
the same shall have become due and payable shall have been fully satisfied and
discharged unless and until the Trustee shall have received a written notice
prior to such date from the Holder hereof stating that the principal of
Securities of Series No. 9 has become due and payable and specifying the amount
of funds required to make such payment.

         Notwithstanding anything to the contrary contained herein, the
aggregate amount of principal actually due on the Securities of Series No. 9
shall not exceed the aggregate amount of the obligations of the Company under
the Credit Agreement.

         If 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.

         This Security is not subject to redemption prior to the Stated Maturity
thereof, other than as set forth in the Indenture.

         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

                                  EXHIBIT A-2

<PAGE>


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.

         This Security is not transferable except to a successor to the
Administrative Agent under the Credit Agreement upon delivery to the Trustee of
a Company Request requesting such transfer. Before any transfer of this Security
will be recognized or given effect by the Company or the Trustee, the Holder
shall note the amounts of all principal prepayments hereon, and shall notify the
Company and the Trustee of the name and address of the transferee and shall
afford the Company and the Trustee the opportunity of verifying the notation as
to prepayment of principal. By the acceptance hereof the Holder of this Security
and each transferee shall be deemed to have agreed to indemnify and hold
harmless the Company and the Trustee against all losses, claims, damages or
liability arising out of any failure on the part of the Holder or of any such
transferee to comply with the requirements of the preceding sentence. Any such
transfer 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.

         This Bond has not been registered under the Securities Act of 1933, as
amended, and may not be offered or sold in contravention of said Act and is not
transferable except to a successor to the Administrative Agent under the Credit
Agreement.

                                  EXHIBIT A-3

<PAGE>


         No service charge shall be made for any such registration of transfer,
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-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:
                                        ---------------------------------------
                                              Vice President and Treasurer




Attest:
       ----------------------------
            Assistant Secretary


                          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





         THIS SECURITY MAY NOT BE TRANSFERRED OR EXCHANGED, NOR MAY ANY
PURPORTED TRANSFER BE REGISTERED, EXCEPT TO A SUCCESSOR TO THE ADMINISTRATIVE
AGENT UNDER THE CREDIT AGREEMENT REFERRED TO HEREIN.

         THE HOLDER OF THIS BOND BY ITS ACCEPTANCE HEREOF AGREES TO RESTRICTIONS
ON TRANSFER, RESTRICTIONS ON VOTING, TO WAIVERS OF CERTAIN RIGHTS OF EXCHANGE,
AND TO INDEMNIFICATION PROVISIONS AS SET FORTH BELOW. IN ADDITION, THE BOND
REPRESENTED BY THIS CERTIFICATE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT
OF 1933 AND SUCH BOND MAY NOT BE TRANSFERRED WITHOUT COMPLIANCE WITH APPLICABLE
SECURITIES LAWS.

         THIS SECURITY IS SUBJECT TO CERTAIN VOTING RESTRICTIONS SET FORTH IN
THAT ISSUANCE AGREEMENT, DATED AS OF SEPTEMBER 26, 2002, BY AND BETWEEN THE
COMPANY AND BANK OF AMERICA, N.A., AS ADMINISTRATIVE AGENT. A COPY OF THE
ISSUANCE AGREEMENT IS ON FILE AT THE OFFICE OF THE TRUSTEE AND IS AVAILABLE UPON
REQUEST.

                               -------------------
                                  EXHIBIT A-5
<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-6

<PAGE>





                                                                      SCHEDULE A


                             SUPPLEMENTAL INDENTURES

<TABLE>
<CAPTION>
    DATE OF                  SERIES OF BONDS               PRINCIPAL               PRINCIPAL
 SUPPLEMENTAL                ---------------             AMOUNT ISSUED               AMOUNT
   INDENTURE                                             -------------            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
</TABLE>



                                  SCHEDULE A-1