Document:

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                             SUPPLEMENTAL INDENTURE

                         (DATED AS OF SEPTEMBER 1, 2003)

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

                       PUBLIC SERVICE COMPANY OF COLORADO

                                       TO

                      U.S. BANK TRUST NATIONAL ASSOCIATION,
                                                       AS TRUSTEE

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

                  CREATING TWO ISSUES OF FIRST MORTGAGE BONDS,
                   COLLATERAL SERIES N AND COLLATERAL SERIES O

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

      (SUPPLEMENTAL TO INDENTURE DATED AS OF DECEMBER 1, 1939, AS AMENDED)

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                  SUPPLEMENTAL INDENTURE, dated as of September 1, 2003, between
PUBLIC SERVICE COMPANY OF COLORADO, a corporation organized and existing under
the laws of the State of Colorado (the "Company"), party of the first part, and
U.S. BANK TRUST NATIONAL ASSOCIATION (FORMERLY FIRST TRUST OF NEW YORK, NATIONAL
ASSOCIATION), a national banking association, as successor trustee (the
"Trustee") to Morgan Guaranty Trust Company of New York (formerly Guaranty Trust
Company of New York), party of the second part.

                  WHEREAS, the Company heretofore executed and delivered to the
Trustee its Indenture, dated as of December 1, 1939 (the "Principal Indenture"),
to secure its First Mortgage Bonds from time to time issued thereunder; and

                  WHEREAS, the Company has heretofore executed and delivered to
the Trustee the Supplemental Indentures referred to in Schedule A hereto for
certain purposes, including the creation of series of bonds, the subjection to
the lien of the Principal Indenture of property acquired after the execution and
delivery thereof, the amendment of certain provisions of the Principal Indenture
and the appointment of the successor Trustee; and

                  WHEREAS, the Principal Indenture as supplemented and amended
by all Supplemental Indentures heretofore executed by the Company and the
Trustee is hereinafter referred to as the "Indenture", and, unless the context
requires otherwise, references herein to Articles and Sections of the Indenture
shall be to Articles and Sections of the Principal Indenture as so amended; and

                  WHEREAS, the Company proposes to create two new series of
First Mortgage Bonds to be designated as First Mortgage Bonds, Collateral Series
N (the "Collateral Series N Bonds") and First Mortgage Bonds, Collateral Series
O (the "Collateral Series O Bonds"), to be issued and delivered to the trustee
under the 1993 Mortgage (as hereinafter defined) as the basis for the
authentication and delivery under the 1993 Mortgage of First Collateral Trust
Bonds, Series No. 14 and First Collateral Trust Bonds, Series No. 15,
respectively, all as hereinafter provided, and to vary in certain respects the
covenants and provisions contained in Article V of the Indenture, to the extent
that such covenants and provisions apply to the Collateral Series N Bonds and
the Collateral Series O Bonds; and

                  WHEREAS, the Company, pursuant to the provisions of the
Indenture, has, by appropriate corporate action, duly resolved and determined to
execute this Supplemental Indenture for the purpose of providing for the
creation of the Collateral Series N Bonds and the Collateral Series O Bonds and
of specifying the form, provisions and particulars thereof, as in the Indenture
provided or permitted and of giving to the Collateral Series N Bonds and the
Collateral Series O Bonds the protection and security of the Indenture; and

                  WHEREAS, the Company represents that all acts and proceedings
required by law and by the charter and by-laws of the Company, including all
action requisite on the part of its shareholders, directors and officers,
necessary to make the Collateral Series N Bonds and the Collateral Series O
Bonds , when executed by the Company, authenticated and delivered by the Trustee
and duly issued, the valid, binding and legal obligations of the Company, and to
constitute the Principal Indenture and all indentures supplemental thereto,
including this

                                       1

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Supplemental Indenture, valid, binding and legal instruments for the security of
the bonds of all series, including the Collateral Series N Bonds and the
Collateral Series O Bonds , in accordance with the terms of such bonds and such
instruments, have been done, performed and fulfilled, and the execution and
delivery hereof have been in all respects duly authorized;

                  NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE WITNESSETH:

                  That Public Service Company of Colorado, the Company named in
the Indenture, in consideration of the premises and of One Dollar to it duly
paid by the Trustee at or before the ensealing and delivery of these presents,
the receipt whereof is hereby acknowledged, and in pursuance of the direction
and authority of the Board of Directors of the Company given at a meeting
thereof duly called and held, and in order to create the Collateral Series N
Bonds and the Collateral Series O Bonds and to specify the form, terms and
provisions thereof, and to secure the payment of the principal of and premium,
if any, and interest, if any, on all bonds from time to time outstanding under
the Indenture, including the Collateral Series N Bonds and the Collateral Series
O Bonds, according to the terms of said bonds, and to secure the performance and
observance of all of the covenants and conditions contained in the Indenture,
has executed and delivered this Supplemental Indenture and has granted,
bargained, sold, warranted, aliened, remised, released, conveyed, assigned,
transferred, mortgaged, pledged, set over and confirmed unto U.S. Bank Trust
National Association, as Trustee, and its successor or successors in the trust
and its and their assigns forever;

                  TO HAVE AND TO HOLD all and singular the properties, rights,
privileges and franchises described in the Principal Indenture and in the
several Supplemental Indentures hereinabove referred to and owned by the Company
on the date of the execution and delivery hereof (other than property of a
character expressly excepted from the lien of the Indenture as therein set
forth) unto the Trustee and its successor or successors and assigns forever;

                  SUBJECT, HOWEVER, to permitted encumbrances as defined in the
Indenture;

                  IN TRUST, NEVERTHELESS, upon the terms and trusts set forth in
the Indenture, for the equal and proportionate benefit and security of all
present and future holders of the bonds and coupons issued and to be issued
under the Indenture, including the Collateral Series N Bonds and the Collateral
Series O Bonds, without preference, priority or distinction as to lien (except
as any sinking, amortization, improvement or other fund established in
accordance with the provisions of the Indenture or any indenture supplemental
thereto may afford additional security for the bonds of any particular series)
of any of said bonds over any others thereof by reason of series, priority in
the time of the issue or negotiation thereof, or otherwise howsoever, except as
provided in Section 2 of Article IV of the Indenture.

                                  ARTICLE ONE

            CREATION AND DESCRIPTION OF THE COLLATERAL SERIES N BONDS

                  SECTION 1. A new series of bonds to be issued under and
secured by the Indenture is hereby created, the bonds of such new series to be
designated First Mortgage Bonds, Collateral Series N. The Collateral Series N
Bonds shall be limited to an aggregate principal

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amount of Three Hundred Million dollars ($300,000,000). The Collateral Series N
Bonds shall mature on October 1, 2008. The Collateral Series N Bonds shall not
bear interest.

                  The principal of each of the Collateral Series N Bonds shall
be payable, upon presentation thereof, at the office or agency of the Company in
the city in which the principal corporate trust office of the 1993 Mortgage
Trustee (as hereinafter defined) is located, in any coin or currency of the
United States of America which at the time of payment shall be legal tender for
the payment of public and private debts.

                  The Collateral Series N Bonds shall be issued and delivered by
the Company to U.S. Bank Trust National Association, as successor trustee under
the Indenture, dated as of October 1, 1993, as supplemented (the "1993
Mortgage"), of the Company to such successor trustee (the "1993 Mortgage
Trustee"), as the basis for the authentication and delivery under the 1993
Mortgage of First Collateral Trust Bonds, Series No. 14. As provided in the 1993
Mortgage, the Collateral Series N Bonds will be registered in the name of the
1993 Mortgage Trustee or its nominee and will be owned and held by the 1993
Mortgage Trustee, subject to the provisions of the 1993 Mortgage, for the
benefit of the holders of all securities from time to time outstanding under the
1993 Mortgage, and the Company shall have no interest therein.

                  Any payment by the Company under the 1993 Mortgage of the
principal of the securities which shall have been authenticated and delivered
under the 1993 Mortgage on the basis of the issuance and delivery to the 1993
Mortgage Trustee of Collateral Series N Bonds (other than by the application of
the proceeds of a payment in respect of such Collateral Series N Bonds), shall,
to the extent thereof, be deemed to satisfy and discharge the obligation of the
Company, if any, to make a payment of principal of such Collateral Series N
Bonds which is then due.

                  The Trustee may conclusively presume that the obligation of
the Company to pay the principal of the Collateral Series N Bonds as the same
shall become due and payable shall have been fully satisfied and discharged
unless and until it shall have received a written notice from the 1993 Mortgage
Trustee, signed by an authorized officer thereof, stating that the principal of
specified Collateral Series N Bonds has become due and payable and has not been
fully paid, and specifying the amount of funds required to make such payment.

                  Each Collateral Series N Bond shall be dated as of the date of
its authentication.

                  The Collateral Series N Bonds shall be issued as fully
registered bonds only, in denominations of $1,000 and multiples thereof.

                  The Collateral Series N Bonds shall be registerable and
exchangeable at the office or agency of the Company in the city in which the
principal corporate trust office of the 1993 Mortgage Trustee is located, in the
manner and upon the terms set forth in Section 5 of Article II of the Indenture;
provided, however, that none of the Collateral Series N Bonds shall be
transferable except to a successor trustee under the 1993 Mortgage. No service
charge shall be made for any exchange or transfer of any Collateral Series N
Bond.

                  SECTION 2. The text of the Collateral Series N Bonds shall be
substantially in the form attached hereto as Exhibit A.

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                  SECTION 3. The Collateral Series N Bonds may be executed by
the Company and delivered to the Trustee and, upon compliance with all
applicable provisions and requirements of the Indenture in respect thereof,
shall be authenticated by the Trustee and delivered (without awaiting the filing
or recording of this Supplemental Indenture) in accordance with the written
order or orders of the Company.

                                  ARTICLE TWO

            CREATION AND DESCRIPTION OF THE COLLATERAL SERIES O BONDS

                  SECTION 1. A new series of bonds to be issued under and
secured by the Indenture is hereby created, the bonds of such new series to be
designated First Mortgage Bonds, Collateral Series O. The Collateral Series O
Bonds shall be limited to an aggregate principal amount of Two Hundred
Seventy-Five Million dollars ($275,000,000). The Collateral Series O Bonds shall
mature on April 1, 2014. The Collateral Series O Bonds shall not bear interest.

                  The principal of each of the Collateral Series O Bonds shall
be payable, upon presentation thereof, at the office or agency of the Company in
the city in which the principal corporate trust office of the 1993 Mortgage
Trustee is located, in any coin or currency of the United States of America
which at the time of payment shall be legal tender for the payment of public and
private debts.

                  The Collateral Series O Bonds shall be issued and delivered by
the Company to the 1993 Mortgage Trustee, as the basis for the authentication
and delivery under the 1993 Mortgage of First Collateral Trust Bonds, Series No.
15. As provided in the 1993 Mortgage, the Collateral Series O Bonds will be
registered in the name of the 1993 Mortgage Trustee or its nominee and will be
owned and held by the 1993 Mortgage Trustee, subject to the provisions of the
1993 Mortgage, for the benefit of the holders of all securities from time to
time outstanding under the 1993 Mortgage, and the Company shall have no interest
therein.

                  Any payment by the Company under the 1993 Mortgage of the
principal of the securities which shall have been authenticated and delivered
under the 1993 Mortgage on the basis of the issuance and delivery to the 1993
Mortgage Trustee of Collateral Series O Bonds (other than by the application of
the proceeds of a payment in respect of such Collateral Series O Bonds), shall,
to the extent thereof, be deemed to satisfy and discharge the obligation of the
Company, if any, to make a payment of principal of such Collateral Series O
Bonds which is then due.

                  The Trustee may conclusively presume that the obligation of
the Company to pay the principal of the Collateral Series O Bonds as the same
shall become due and payable shall have been fully satisfied and discharged
unless and until it shall have received a written notice from the 1993 Mortgage
Trustee, signed by an authorized officer thereof, stating that the principal of
specified Collateral Series O Bonds has become due and payable and has not been
fully paid, and specifying the amount of funds required to make such payment.

                  Each Collateral Series O Bond shall be dated as of the date of
its authentication.

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                  The Collateral Series O Bonds shall be issued as fully
registered bonds only, in denominations of $1,000 and multiples thereof.

                  The Collateral Series O Bonds shall be registerable and
exchangeable at the office or agency of the Company in the city in which the
principal corporate trust office of the 1993 Mortgage Trustee is located, in the
manner and upon the terms set forth in Section 5 of Article II of the Indenture;
provided, however, that none of the Collateral Series O Bonds shall be
transferable except to a successor trustee under the 1993 Mortgage. No service
charge shall be made for any exchange or transfer of any Collateral Series O
Bond.

                  SECTION 2. The text of the Collateral Series O Bonds shall be
substantially in the form attached hereto as Exhibit B.

                  SECTION 3. The Collateral Series O Bonds may be executed by
the Company and delivered to the Trustee and, upon compliance with all
applicable provisions and requirements of the Indenture in respect thereof,
shall be authenticated by the Trustee and delivered (without awaiting the filing
or recording of this Supplemental Indenture) in accordance with the written
order or orders of the Company.

                                 ARTICLE THREE

                   REDEMPTION OF THE COLLATERAL SERIES N BONDS
                        AND THE COLLATERAL SERIES O BONDS

                  SECTION 1. Each Collateral Series N Bond and Collateral Series
Bond shall be redeemable at the option of the Company in whole at any time, or
in part from time to time, prior to maturity, at a redemption price equal to
100% of the principal amount thereof to be redeemed.

                  SECTION 2. The provisions of Sections 3, 4, 5, 6 and 7 of
Article V of the Indenture shall be applicable to the Collateral Series N Bonds
and the Collateral Series O Bonds, except that (a) no publication of notice of
redemption of the Collateral Series N Bonds or the Collateral Series O Bonds
shall be required and (b) if less than all the Collateral Series N Bonds or the
Collateral Series O Bonds are to be redeemed, the Collateral Series N Bonds or
the Collateral Series O Bonds to be redeemed shall be selected in the principal
amounts designated to the Trustee by the Company, and except as such provisions
may otherwise be inconsistent with the provisions of this Article Three.

                  SECTION 3. The holder of each and every Collateral Series N
Bond and Collateral Series O Bond hereby agrees to accept payment thereof prior
to maturity on the terms and conditions provided for in this Article Three.

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                                  ARTICLE FOUR

                         ACKNOWLEDGMENT OF RIGHT TO VOTE
                           OR CONSENT WITH RESPECT TO
                         CERTAIN AMENDMENTS TO INDENTURE

                  The Company hereby acknowledges the right of the holders of
the Collateral Series N Bonds and the Collateral Series O Bonds to vote or
consent with respect to any or all of the modifications to the Indenture
referred to in Article Three of the Supplemental Indenture, dated as of March 1,
1980, irrespective of the fact that the Bonds of the Second 1987 Series are no
longer outstanding; provided, however, that such acknowledgment shall not impair
(a) the right of the Company to make such modifications without the consent or
other action of the holders of the Bonds of the 2020 Series or the bonds of any
other series subsequently created under the Indenture with respect to which the
Company has expressly reserved such right or (b) the right of the Company to
reserve the right to make such modifications without the consent or other action
of the holders of bonds of one or more, or any or all, series created subsequent
to the creation of the Collateral Series N Bonds and the Collateral Series O
Bonds.

                                  ARTICLE FIVE

                                   THE TRUSTEE

                  The Trustee accepts the trusts created by this Supplemental
Indenture upon the terms and conditions set forth in the Indenture and this
Supplemental Indenture. The recitals in this Supplemental Indenture are made by
the Company only and not by the Trustee. Each and every term and condition
contained in Article XII of the Indenture shall apply to this Supplemental
Indenture with the same force and effect as if the same were herein set forth in
full, with such omissions, variations and modifications thereof as may be
appropriate to make the same conform to this Supplemental Indenture.

                                  ARTICLE SIX

                            MISCELLANEOUS PROVISIONS

                  SECTION 1. Subject to the variations contained in Article
Three of this Supplemental Indenture, the Indenture is in all respects ratified
and confirmed and the Principal Indenture, this Supplemental Indenture and all
other indentures supplemental to the Principal Indenture shall be read, taken
and construed as one and the same instrument. Neither the execution of this
Supplemental Indenture nor anything herein contained shall be construed to
impair the lien of the Indenture on any of the properties subject thereto, and
such lien shall remain in full force and effect as security for all bonds now
outstanding or hereafter issued under the Indenture.

                  All covenants and provisions of the Indenture shall continue
in full force and effect and this Supplemental Indenture shall form part of the
Indenture.

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                  SECTION 2. If the date for making any payment or the last date
for performance of any act or the exercising of any right, as provided in this
Supplemental Indenture, shall not be a Business Day (as defined in the 1993
Mortgage), such payment may be made or act performed or right exercised on the
next succeeding Business Day with the same force and effect as if done on the
nominal date provided in this Supplemental Indenture.

                  SECTION 3. The terms defined in the Indenture shall, for all
purposes of this Supplemental Indenture, have the meaning specified in the
Indenture except as set forth in Section 4 of this Article or otherwise set
forth in this Supplemental Indenture or unless the context clearly indicates
some other meaning to be intended.

                  SECTION 4. Any term defined in Section 303 of the Trust
Indenture Act of 1939, as amended, and not otherwise defined in the Indenture
shall, with respect to this Supplemental Indenture, the Collateral Series N
Bonds and the Collateral Series O Bonds, have the meaning assigned to such term
in Section 303 as in force on the date of the execution of this Supplemental
Indenture.

                  SECTION 5. This Supplemental Indenture may be executed in any
number of counterparts, and all of said counterparts executed and delivered,
each as an original, shall constitute but one and the same instrument.

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                  IN WITNESS WHEREOF, Public Service Company of Colorado, party
hereto of the first part, has caused its corporate name to be hereunto affixed,
and this instrument to be signed by its President, an Executive Vice President,
a Senior Vice President or a Vice President, and its corporate seal to be
hereunto affixed and attested by its Secretary or an Assistant Secretary for and
in its behalf; and U.S. Bank Trust National Association, the party hereto of the
second part, in evidence of its acceptance of the trust hereby created, has
caused its corporate name to be hereunto affixed, and this instrument to be
signed and its corporate seal to be affixed by one of its Assistant Vice
Presidents and attested by one of its Trust Officers, for and in its behalf, all
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

ATTEST: /s/ Anne M. Ziebell
        -------------------------------------
        Name:  Anne M. Ziebell
        Title: Assistant Secretary

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

                  On this 1st day of September, 2003, before me, Sharon M.
Quellhorst, a duly authorized Notary Public in and for said City in the State
aforesaid, personally appeared Benjamin G. S. Fowke III and Anne M. Ziebell to
me known to be a Vice President and Treasurer and the Assistant Secretary,
respectively, of PUBLIC SERVICE COMPANY OF COLORADO, a corporation organized and
existing under the laws of the State of Colorado, one of the corporations that
executed the within and foregoing instrument; and the said Vice President and
Treasurer and Assistant Secretary severally acknowledged the said instrument to
be the free and voluntary act and deed of said corporation, for the uses and
purposes therein mentioned, and on oath stated that they were authorized to
execute said instrument and that the seal affixed thereto is the corporate seal
of said corporation.

                  IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                         /s/ Sharon M. Quellhorst
                                     ---------------------------------------
                                     Name:  Sharon M. Quellhorst
                                     Notary Public, State of Minnesota
                                     Commission Expires:  January 31, 2005

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                                 U.S. BANK TRUST
                                  NATIONAL ASSOCIATION,
                                     as Trustee

                                 By: /s/ Ignazio Tamburello
                                     -----------------------------------------
                                     Name:  Ignazio Tamburello
                                     Title: Assistant Vice President

ATTEST: /s/ Adam Berman
        -------------------------------
        Name:  Adam Berman
        Title: Trust Officer

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

                  On this 2nd day of September, 2003, before me, Rouba Fakih, a
duly authorized Notary Public in and for said City and County in the State
aforesaid, personally appeared Ignazio Tamburello and Adam Berman to me known to
be an Assistant Vice President and a Trust Officer, respectively, of U.S. BANK
TRUST NATIONAL ASSOCIATION, a national banking association, one of the
corporations that executed the within and foregoing instrument; and the said
Assistant Vice President and Trust Officer severally acknowledged the said
instrument to be the free and voluntary act and deed of said corporation, for
the uses and purposes therein mentioned, and on oath stated that they were
authorized to execute said instrument and that the seal affixed thereto is the
corporate seal of said corporation.

                  IN WITNESS WHEREOF, I have hereunto set my hand and affixed my
official seal the day and year first above written.

                                 /s/ Rouba Fakih
                                 ----------------------------------------------
                                 Name: Rouba Fakih
                                 Notary Public, State of New York

                                 Commission Expires: February 20, 2007

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                                                                       EXHIBIT A

                        FORM OF COLLATERAL SERIES N BOND

         THIS BOND IS NOT TRANSFERABLE EXCEPT TO A SUCCESSOR TRUSTEE UNDER THE
INDENTURE, DATED AS OF OCTOBER 1, 1993, AS SUPPLEMENTED, BETWEEN PUBLIC SERVICE
COMPANY OF COLORADO AND U.S. BANK TRUST NATIONAL ASSOCIATION (FORMERLY FIRST
TRUST OF NEW YORK, NATIONAL ASSOCIATION), AS SUCCESSOR TRUSTEE THEREUNDER.

                       PUBLIC SERVICE COMPANY OF COLORADO

                              FIRST MORTGAGE BOND,

                               Collateral Series N

                                    DUE 2008

REGISTERED                                                          REGISTERED

No. _________________                                        $__________________

         FOR VALUE RECEIVED, PUBLIC SERVICE COMPANY OF COLORADO, a corporation
organized and existing under the laws of the State of Colorado (hereinafter
sometimes called the "Company"), promises to pay to U.S. Bank Trust National
Association (formerly known as First Trust of New York, National Association),
as successor trustee (the "1993 Mortgage Trustee") under the Indenture, dated as
of October 1, 1993 (the "1993 Mortgage"), of the Company, or registered assigns,

                                                                         Dollars
on October 1, 2008, at the office or agency of the Company in the city in which
the principal corporate trust office of the 1993 Mortgage Trustee is located.
This bond shall not bear interest. The principal of this bond shall be payable
in any coin or currency of the United States of America which at the time of
payment shall be legal tender for the payment of public and private debts.

         Any payment by the Company under the 1993 Mortgage of the principal of
securities which shall have been authenticated and delivered under the 1993
Mortgage on the basis of the issuance and delivery to the 1993 Mortgage Trustee
of this bond (other than by the application of the proceeds of a payment in
respect of this bond) shall, to the extent thereof, be deemed to satisfy and
discharge the obligation of the Company, if any, to make a payment of principal
of this bond which is then due.

         This bond is one of an issue of bonds of the Company, issued and to be
issued in one or more series under and equally and ratably secured (except as
any sinking, amortization, improvement or other fund, established in accordance
with the provisions of the indenture

                                   Exhibit A-1

<PAGE>

hereinafter mentioned, may afford additional security for the bonds of any
particular series) by a certain indenture, dated as of December 1, 1939, made by
the Company to U.S. BANK TRUST NATIONAL ASSOCIATION (formerly First Trust of New
York, National Association), as successor trustee (hereinafter called the
"Trustee") to Morgan Guaranty Trust Company of New York (formerly Guaranty Trust
Company of New York), as amended and supplemented by several indentures
supplemental thereto, including the Supplemental Indenture dated as of September
1, 2003 (said Indenture as amended and supplemented by said indentures
supplemental thereto being hereinafter called the "Indenture"), to which
Indenture reference is hereby made for a description of the property mortgaged,
the nature and extent of the security, the rights and limitations of rights of
the Company, the Trustee, and the holders of said bonds, under the Indenture,
and the terms and conditions upon which said bonds are secured, to all of the
provisions of which Indenture and of all indentures supplemental thereto in
respect of such security, including the provisions of the Indenture permitting
the issue of bonds of any series for property which, under the restrictions and
limitations therein specified, may be subject to liens prior to the lien of the
Indenture, the holder, by accepting this bond, assents. To the extent permitted
by and as provided in the Indenture, the rights and obligations of the Company
and of the holders of said bonds (including those pertaining to any sinking or
other fund) may be changed and modified, with the consent of the Company, by the
holders of at least 75% in aggregate principal amount of the bonds then
outstanding (excluding bonds disqualified from voting by reason of the Company's
interest therein as provided in the Indenture); provided, however, that without
the consent of the holder hereof no such modification or alteration shall be
made which will extend the time of payment of the principal of this bond or
reduce the principal amount hereof or effect any other modification of the terms
of payment of such principal or will reduce the percentage of bonds required for
the aforesaid actions under the Indenture. The Company has reserved the right to
amend the Indenture without any consent or other action by holders of any series
of bonds created after October 31, 1975 (including this series) so as to change
75% in the foregoing sentence to 60% and to change certain procedures relating
to bondholders' meetings. This bond is one of a series of bonds designated as
the First Mortgage Bonds, Collateral Series N, of the Company.

         This bond shall be redeemable at the option of the Company in whole at
any time, or in part from time to time, prior to maturity, at a redemption price
equal to 100% of the principal amount thereof to be redeemed.

         The principal of this bond may be declared or may become due before the
maturity hereof, on the conditions, in the manner and at the times set forth in
the Indenture, upon the happening of an event of default as therein provided.

         This bond is not transferable except to a successor trustee under the
1993 Mortgage, any such transfer to be made at the office or agency of the
Company in the city in which the principal corporate trust office of the 1993
Mortgage Trustee is located, upon surrender and cancellation of this bond, and
thereupon a new bond of this series of a like principal amount will be issued to
the transferee in exchange therefor, as provided in the Indenture. The Company,
the Trustee, any paying agent and any registrar may deem and treat the person in
whose name this bond is registered as the absolute owner hereof for the purpose
of receiving payment and for all other purposes. This bond, alone or with other
bonds of this series, may in like manner be exchanged at such office or agency
for one or more new bonds of this series of the same aggregate principal

                                   Exhibit A-2

<PAGE>

amount, all as provided in the Indenture. No service charge shall be made to any
holder of any bond of this series for any exchange or transfer of bonds.

         No recourse under or upon any covenant or obligation of the Indenture,
or of any bonds thereby secured, or for any claim based thereon, or otherwise in
any manner in respect thereof, shall be had against any incorporator, subscriber
to the capital stock, shareholder, officer or director, as such, of the Company,
whether former, present or future, either directly, or indirectly through the
Company or the Trustee, by the enforcement of any subscription to capital stock,
assessment or otherwise, or by any legal or equitable proceeding by virtue of
any statute or otherwise (including, without limiting the generality of the
foregoing, any proceeding to enforce any claimed liability of shareholders of
the Company based upon any theory of disregarding the corporate entity of the
Company or upon any theory that the Company was acting as the agent or
instrumentality of the shareholders), any and all such liability of
incorporators, shareholders, subscribers, officers and directors, as such, being
released by the holder hereof, by the acceptance of this bond, and being
likewise waived and released by the terms of the Indenture under which this bond
is issued.

         This bond shall not be valid or become obligatory for any purpose until
the certificate of authentication endorsed hereon shall have been signed by U.S.
Bank Trust National Association, or its successor, as Trustee under the
Indenture.

         IN WITNESS WHEREOF, Public Service Company of Colorado has caused this
bond to be signed in its name by a Vice President and its corporate seal to be
affixed hereto and attested by its Secretary or an Assistant Secretary.

Dated:                           PUBLIC SERVICE COMPANY OF
                                 COLORADO

                                 By: ______________________________
                                      [Vice President]

ATTEST:________________________
       [Assistant Secretary]

                          CERTIFICATE OF AUTHENTICATION

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

Dated:                           U.S. BANK TRUST
                                 NATIONAL ASSOCIATION,
                                    AS TRUSTEE

                                 By: ______________________________
                                                 Authorized Officer

                                   Exhibit A-3

<PAGE>

                                                                       EXHIBIT B

                        FORM OF COLLATERAL SERIES O BOND

         THIS BOND IS NOT TRANSFERABLE EXCEPT TO A SUCCESSOR TRUSTEE UNDER THE
INDENTURE, DATED AS OF OCTOBER 1, 1993, AS SUPPLEMENTED, BETWEEN PUBLIC SERVICE
COMPANY OF COLORADO AND U.S. BANK TRUST NATIONAL ASSOCIATION (FORMERLY FIRST
TRUST OF NEW YORK, NATIONAL ASSOCIATION), AS SUCCESSOR TRUSTEE THEREUNDER.

                       PUBLIC SERVICE COMPANY OF COLORADO

                              FIRST MORTGAGE BOND,

                               Collateral Series O

                                    DUE 2014

REGISTERED                                                       REGISTERED

No._______________                                               $______________

         FOR VALUE RECEIVED, PUBLIC SERVICE COMPANY OF COLORADO, a corporation
organized and existing under the laws of the State of Colorado (hereinafter
sometimes called the "Company"), promises to pay to U.S. Bank Trust National
Association (formerly known as First Trust of New York, National Association),
as successor trustee (the "1993 Mortgage Trustee") under the Indenture, dated as
of October 1, 1993 (the "1993 Mortgage"), of the Company, or registered assigns,

                                                                         Dollars
on April 1, 2014, at the office or agency of the Company in the city in which
the principal corporate trust office of the 1993 Mortgage Trustee is located.
This bond shall not bear interest. The principal of this bond shall be payable
in any coin or currency of the United States of America which at the time of
payment shall be legal tender for the payment of public and private debts.

         Any payment by the Company under the 1993 Mortgage of the principal of
securities which shall have been authenticated and delivered under the 1993
Mortgage on the basis of the issuance and delivery to the 1993 Mortgage Trustee
of this bond (other than by the application of the proceeds of a payment in
respect of this bond) shall, to the extent thereof, be deemed to satisfy and
discharge the obligation of the Company, if any, to make a payment of principal
of this bond which is then due.

         This bond is one of an issue of bonds of the Company, issued and to be
issued in one or more series under and equally and ratably secured (except as
any sinking, amortization, improvement or other fund, established in accordance
with the provisions of the indenture

                                   Exhibit B-1

<PAGE>

hereinafter mentioned, may afford additional security for the bonds of any
particular series) by a certain indenture, dated as of December 1, 1939, made by
the Company to U.S. BANK TRUST NATIONAL ASSOCIATION (formerly First Trust of New
York, National Association), as successor trustee (hereinafter called the
"Trustee") to Morgan Guaranty Trust Company of New York (formerly Guaranty Trust
Company of New York), as amended and supplemented by several indentures
supplemental thereto, including the Supplemental Indenture dated as of September
1, 2003 (said Indenture as amended and supplemented by said indentures
supplemental thereto being hereinafter called the "Indenture"), to which
Indenture reference is hereby made for a description of the property mortgaged,
the nature and extent of the security, the rights and limitations of rights of
the Company, the Trustee, and the holders of said bonds, under the Indenture,
and the terms and conditions upon which said bonds are secured, to all of the
provisions of which Indenture and of all indentures supplemental thereto in
respect of such security, including the provisions of the Indenture permitting
the issue of bonds of any series for property which, under the restrictions and
limitations therein specified, may be subject to liens prior to the lien of the
Indenture, the holder, by accepting this bond, assents. To the extent permitted
by and as provided in the Indenture, the rights and obligations of the Company
and of the holders of said bonds (including those pertaining to any sinking or
other fund) may be changed and modified, with the consent of the Company, by the
holders of at least 75% in aggregate principal amount of the bonds then
outstanding (excluding bonds disqualified from voting by reason of the Company's
interest therein as provided in the Indenture); provided, however, that without
the consent of the holder hereof no such modification or alteration shall be
made which will extend the time of payment of the principal of this bond or
reduce the principal amount hereof or effect any other modification of the terms
of payment of such principal or will reduce the percentage of bonds required for
the aforesaid actions under the Indenture. The Company has reserved the right to
amend the Indenture without any consent or other action by holders of any series
of bonds created after October 31, 1975 (including this series) so as to change
75% in the foregoing sentence to 60% and to change certain procedures relating
to bondholders' meetings. This bond is one of a series of bonds designated as
the First Mortgage Bonds, Collateral Series O, of the Company.

         This bond shall be redeemable at the option of the Company in whole at
any time, or in part from time to time, prior to maturity, at a redemption price
equal to 100% of the principal amount thereof to be redeemed.

         The principal of this bond may be declared or may become due before the
maturity hereof, on the conditions, in the manner and at the times set forth in
the Indenture, upon the happening of an event of default as therein provided.

         This bond is not transferable except to a successor trustee under the
1993 Mortgage, any such transfer to be made at the office or agency of the
Company in the city in which the principal corporate trust office of the 1993
Mortgage Trustee is located, upon surrender and cancellation of this bond, and
thereupon a new bond of this series of a like principal amount will be issued to
the transferee in exchange therefor, as provided in the Indenture. The Company,
the Trustee, any paying agent and any registrar may deem and treat the person in
whose name this bond is registered as the absolute owner hereof for the purpose
of receiving payment and for all other purposes. This bond, alone or with other
bonds of this series, may in like manner be exchanged at such office or agency
for one or more new bonds of this series of the same aggregate principal

                                   Exhibit B-2

<PAGE>

amount, all as provided in the Indenture. No service charge shall be made to any
holder of any bond of this series for any exchange or transfer of bonds.

         No recourse under or upon any covenant or obligation of the Indenture,
or of any bonds thereby secured, or for any claim based thereon, or otherwise in
any manner in respect thereof, shall be had against any incorporator, subscriber
to the capital stock, shareholder, officer or director, as such, of the Company,
whether former, present or future, either directly, or indirectly through the
Company or the Trustee, by the enforcement of any subscription to capital stock,
assessment or otherwise, or by any legal or equitable proceeding by virtue of
any statute or otherwise (including, without limiting the generality of the
foregoing, any proceeding to enforce any claimed liability of shareholders of
the Company based upon any theory of disregarding the corporate entity of the
Company or upon any theory that the Company was acting as the agent or
instrumentality of the shareholders), any and all such liability of
incorporators, shareholders, subscribers, officers and directors, as such, being
released by the holder hereof, by the acceptance of this bond, and being
likewise waived and released by the terms of the Indenture under which this bond
is issued.

         This bond shall not be valid or become obligatory for any purpose until
the certificate of authentication endorsed hereon shall have been signed by U.S.
Bank Trust National Association, or its successor, as Trustee under the
Indenture.

         IN WITNESS WHEREOF, Public Service Company of Colorado has caused this
bond to be signed in its name by a Vice President and its corporate seal to be
affixed hereto and attested by its Secretary or an Assistant Secretary.

Dated:                           PUBLIC SERVICE COMPANY OF
                                 COLORADO

                                 By: __________________________
                                     [Vice President]

ATTEST:________________________
      [Assistant Secretary]

                          CERTIFICATE OF AUTHENTICATION

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

Dated:                           U.S. BANK TRUST
                                 NATIONAL ASSOCIATION,
                                      AS TRUSTEE

                                 By: _________________________________
                                                    Authorized Officer

                                   Exhibit B-3

<PAGE>

                                                                      SCHEDULE A

                             SUPPLEMENTAL INDENTURES

<TABLE>
<CAPTION>
    DATE OF                                                                                       PRINCIPAL
 SUPPLEMENTAL                                                         PRINCIPAL                     AMOUNT
   INDENTURE                        SERIES OF BONDS                 AMOUNT ISSUED                OUTSTANDING
   ---------                        ---------------                 -------------                -----------
<S>                                <C>                             <C>                           <C>
March 14, 1941                              None                                --                    --
May 14, 1941                                None                                --                    --
April 28, 1942                              None                                --                    --
April 14, 1943                              None                                --                    --
April 27, 1944                              None                                --                    --
April 18, 1945                              None                                --                    --
April 23, 1946                              None                                --                    --
April 9, 1947                               None                                --                    --
June 1, 1947*                      2-7/8% Series due 1977          $    40,000,000                  None
April 1, 1948                               None                                --                    --
May 20, 1948                                None                                --                    --
October 1, 1948                    3-1/8% Series due 1978               10,000,000                  None
April 20, 1949                              None                                --                    --
April 24, 1950                              None                                --                    --
April 18, 1951                              None                                --                    --
October 1, 1951                    3-1/4% Series due 1981               15,000,000                  None
April 21, 1952                              None                                --                    --
December 1, 1952                            None                                --                    --
April 15, 1953                              None                                --                    --
April 19, 1954                              None                                --                    --
October 1, 1954*                   3-1/8% Series due 1984               20,000,000                  None
April 18, 1955                              None                                --                    --
April 24, 1956                              None                                --                    --
May 1, 1957*                       4-3/8% Series due 1987               30,000,000                  None
April 10, 1958                              None                                --                    --
May 1, 1959                        4-5/8% Series due 1989               20,000,000                  None
April 18, 1960                              None                                --                    --
April 19, 1961                              None                                --                    --
October 1, 1961                    4-1/2% Series due 1991               30,000,000                  None
March 1, 1962                      4-5/8% Series due 1992                8,800,000                  None
June 1, 1964                       4-1/2% Series due 1994               35,000,000                  None
May 1, 1966                        5-3/8% Series due 1996               35,000,000                  None
July 1, 1967*                      5-7/8% Series due 1997               35,000,000                  None
July 1, 1968*                      6-3/4% Series due 1998               25,000,000                  None
April 25, 1969                              None                                --                    --
</TABLE>

                                  Schedule A-1
<PAGE>

<TABLE>
<CAPTION>
  DATE OF                                                                                         PRINCIPAL
SUPPLEMENTAL                                                          PRINCIPAL                    AMOUNT
 INDENTURE                           SERIES OF BONDS                AMOUNT ISSUED                OUTSTANDING
------------                         ---------------                -------------                -----------
<S>                         <C>                                     <C>                          <C>
April 21, 1970                              None                                --                     --
September 1, 1970                  8-3/4% Series due 2000               35,000,000                   None
February 1, 1971                   7-1/4% Series due 2001               40,000,000                   None
August 1, 1972                     7-1/2% Series due 2002               50,000,000                   None
June 1, 1973                       7-5/8% Series due 2003               50,000,000                   None
March 1, 1974                    Pollution Control Series A             24,000,000                   None
December 1, 1974                 Pollution Control Series B             50,000,000                   None
October 1, 1975                    9-3/8% Series due 2005               50,000,000                   None
April 28, 1976                              None                                --                     --

April 28, 1977                              None                                --                     --
November 1, 1977*                  8-1/4% Series due 2007               50,000,000                   None
April 28, 1978                              None                                --                     --
October 1, 1978                    9-1/4% Series due 2008               50,000,000                   None
October 1, 1979*                 Pollution Control Series C             50,000,000                   None
March 1, 1980*                      15% Series due 1987                 50,000,000                   None
April 28, 1981                              None                                --                     --
November 1, 1981*                Pollution Control Series D             27,380,000                   None
December 1, 1981*                 16-1/4% Series due 2011               50,000,000                   None
April 29, 1982                              None                                --                     --
May 1, 1983*                     Pollution Control Series E             42,000,000                   None

April 30, 1984                              None                                --                     --
March 1, 1985*                      13% Series due 2015                 50,000,000                   None
November 1, 1986*                Pollution Control Series F             27,250,000                   None
May 1, 1987*                       8.95% Series due 1992                75,000,000                   None
July 1, 1990*                      9-7/8% Series due 2020               75,000,000                   None
December 1, 1990*           Secured Medium-Term Notes, Series A        191,500,000**                 None
March 1, 1992*                   8-1/8% Series due 2004 and            100,000,000               100,000,000
                                   8-3/4% Series due 2022              150,000,000                   None
April 1, 1993*                   Pollution Control Series G             79,500,000                79,500,000
June 1, 1993*                    Pollution Control Series H             50,000,000                50,000,000
November 1, 1993*                   Collateral Series A                134,500,000               134,500,000

January 1, 1994*              Collateral Series B due 2001 and         102,667,000                   None
                                Collateral Series B due 2024           110,000,000               110,000,000
September 2, 1994                           None                                --                     --
(Appointment of
Successor Trustee)
May 1, 1996                         Collateral Series C                125,000,000               125,000,000
</TABLE>

                                  Schedule A-2

<PAGE>

<TABLE>
<CAPTION>
  DATE OF                                                                                         PRINCIPAL
SUPPLEMENTAL                                                          PRINCIPAL                    AMOUNT
 INDENTURE                           SERIES OF BONDS                AMOUNT ISSUED                OUTSTANDING
 ---------                           ---------------                -------------                -----------
<S>                                 <C>                             <C>                          <C>
November 1, 1996                    Collateral Series D              250,000,000                 175,000,000
February 1, 1997                    Collateral Series E              150,000,000                    None
April 1, 1998                       Collateral Series F              250,000,000                    None
August 15, 2002                     Collateral Series G               48,750,000                  48,750,000
September 1, 2002                   Collateral Series H              600,000,000                    None
September 15, 2002                  Collateral Series I              530,000,000                    None
April 1, 2003                       Collateral Series J              600,000,000                 600,000,000
March 1, 2003                       Collateral Series K              250,000,000                 250,000,000
May 1, 2003                         Collateral Series M              350,000,000                 350,000,000
</TABLE>

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

* Contains amendatory provisions

** $200,000,000 authorized

                                  Schedule A-3<PAGE>

                             PUBLIC SERVICE COMPANY
                                   OF COLORADO

                                       TO

                      U.S. BANK TRUST NATIONAL ASSOCIATION,

                                             AS TRUSTEE

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

                          SUPPLEMENTAL INDENTURE NO. 15

                          Dated as of September 1, 2003

                          Supplemental to the Indenture
                           dated as of October 1, 1993

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

         Establishing the Securities of Series No. 14 and Series No. 15,
           designated First Collateral Trust Bonds, Series No. 14 and
            First Collateral Trust Bonds, Series No. 15, respectively

<PAGE>

         SUPPLEMENTAL INDENTURE NO. 15, dated as of September 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. 15. 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 two new series of Securities to be
designated "First Collateral Trust Bonds, Series No. 14" and "First Collateral
Trust Bonds, Series No. 15", such series of Securities to be hereinafter
sometimes called "Series No. 14" and "Series No. 15," respectively.

         The Company has duly authorized the execution and delivery of this
Supplemental Indenture No. 15 to establish the Securities of Series No. 14 and
Series No. 15 and has duly authorized the issuance of such Securities; and all
acts necessary to make this Supplemental Indenture No. 15 a valid agreement of
the Company, and to make the Securities of Series No. 14 and Series No. 15 valid
obligations of the Company, have been performed.

                                GRANTING CLAUSES

         NOW, THEREFORE, THIS SUPPLEMENTAL INDENTURE NO. 15 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. 15, 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

<PAGE>

         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. 15 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. 15;

                             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. 14

         There are hereby established the Securities of Series No. 14, 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 Series No. 14 shall be "First
         Collateral Trust Bonds, Series No. 14"; 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 the Securities, to change the title of
         the series 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. 14 shall be initially
         authenticated and delivered in the aggregate principal amount of
         $300,000,000;

         (c)      interest on the Securities of Series No. 14 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. 14 shall be
         payable on October 1, 2008, the Stated Maturity for Series No. 14;

         (e)      the Securities of Series No. 14 shall bear interest at a rate
         of 4.375% per annum; interest shall accrue on the Securities of Series
         No. 14 from September 9, 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 April 1 and October 1 in each year,
         commencing April 1, 2004, and the Regular Record Dates with respect to
         the Interest Payment Dates for such Securities shall be March 15 and
         September 15 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. 14 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. 14 shall be redeemable at the
         option of the Company at any time prior to their 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 15 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 the Independent Investment Banker as having a
         maturity comparable to the remaining term of the Securities of Series
         No. 14 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. 14.

                  "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., McDonald Investments Inc. or UBS Securities LLC and any
         other Primary Treasury Dealer

                                       4

<PAGE>

         designated by, and not affiliated with, Banc One Capital Markets, Inc.,
         McDonald Investments Inc. or UBS Securities LLC and their respective
         successors, provided, however, that if any of the foregoing or any of
         its 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)      not applicable;

         (p)      not applicable;

         (q)      the Securities of Series No. 14 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 Depositary has ceased to be a
                           clearing agency registered under the

                                       5

<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; or

                           (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;

         (r)      not applicable;

         (s)      no service charge shall be made for the registration of
         transfer or exchange of the Securities of Series No. 14; 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. 14 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

                                       6

<PAGE>

                  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. 14 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. 14 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

                           SECURITIES OF SERIES NO. 15

         There are hereby established the Securities of Series No. 15, 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 Series No. 15 shall be "First
         Collateral Trust Bonds, Series No. 15"; 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 the Securities, to change the title of
         the series 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. 15 shall be initially
         authenticated and delivered in the aggregate principal amount of
         $275,000,000;

         (c)      interest on the Securities of Series No. 15 shall be payable
         to the Persons in whose names such Securities are registered at the
         close of business on the Regular

                                       7

<PAGE>

         Record Date for such interest, except as otherwise expressly provided
         in the form of such Securities attached as Exhibit B hereto;

         (d)      the principal of the Securities of Series No. 15 shall be
         payable on April 1, 2014, the Stated Maturity for Series No. 15;

         (e)      the Securities of Series No. 15 shall bear interest at a rate
         of 5.50% per annum; interest shall accrue on the Securities of Series
         No. 15 from September 9, 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 April 1 and October 1 in each year,
         commencing April 1, 2004, and the Regular Record Dates with respect to
         the Interest Payment Dates for such Securities shall be March 15 and
         September 15 in each year, respectively (whether or not a Business
         Day);

         (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. 15 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. 15 shall be redeemable at the
         option of the Company at any time prior to their 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 the Independent Investment Banker as having a
         maturity comparable to the remaining term of the Securities of Series
         No. 15 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. 15.

                  "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

                                       8

<PAGE>

         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., McDonald Investments Inc. or UBS Securities LLC and any
         other Primary Treasury Dealer designated by, and not affiliated with,
         Banc One Capital Markets, Inc., McDonald Investments Inc. or UBS
         Securities LLC and their respective successors, provided, however, that
         if any of the foregoing or any of its 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)      not applicable;

         (p)      not applicable;

         (q)      the Securities of Series No. 15 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:

                                       9

<PAGE>

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

                           (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;

         (r)      not applicable;

         (s)      no service charge shall be made for the registration of
         transfer or exchange of the Securities of Series No. 15; 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. 15 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

                                       10

<PAGE>

         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.

         (i)      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.

         (ii)     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. 15 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. 15 shall be substantially in the form
attached hereto as Exhibit B and shall have such further terms as are set forth
in such form.

                                       11

<PAGE>

                                 ARTICLE THREE

                            MISCELLANEOUS PROVISIONS

         This Supplemental Indenture No. 15 is a supplement to the Original
Indenture. As previously supplemented and further supplemented by this
Supplemental Indenture No. 15, the Original Indenture is in all respects
ratified, approved and confirmed, and the Original Indenture, all previous
supplements thereto and this Supplemental Indenture No. 15 shall together
constitute one and the same instrument.

                                       12

<PAGE>

                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture No. 15 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 1st day of September, 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/ Sharon M. Quellhorst
                                      ------------------------------------------
                                      Name: Sharon M. Quellhorst
                                      Notary Public, State of Minnesota

                                      Commission Expires:  January 31, 2005

                                       13

<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 2nd day of September, 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

                                       14

<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. 14

         Original Interest Accrual Date        September 9, 2003
                         Interest Rate:        4.375%
                       Stated Maturity:        October 1, 2008
                Interest Payment Dates:        April 1 and October 1
                  Regular Record Dates:        March 15 and September 15

                    This Security is not a Discount Security

              within the meaning of the within-mentioned Indenture

Principal Amount                                               Registered No.
$                                                              CUSIP 744448 BW 0

         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 April 1, 2004, 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.

                                   EXHIBIT 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 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 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 15 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 the Independent Investment Banker as having a maturity comparable to
the remaining term of the Securities of Series No. 14 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. 14.

                                   EXHIBIT A-2

<PAGE>

         "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., McDonald Investments Inc. or UBS Securities LLC and any other Primary
Treasury Dealer designated by, and not affiliated with, Banc One Capital
Markets, Inc., McDonald Investments Inc. or UBS Securities LLC and their
respective successors, provided, however, that if any of the foregoing or any of
its 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 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

                                  EXHIBIT A-3

<PAGE>

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.

         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.

                                  EXHIBIT A-4

<PAGE>

         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.

         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

                                  EXHIBIT A-6

<PAGE>

SECURITIES DEPOSITARY WITH RESPECT TO THE SECURITIES; OR (B) THE COMPANY SHALL
HAVE DELIVERED TO THE TRUSTEE A COMPANY ORDER TO THE EFFECT THAT THE SECURITIES
SHALL BE SO EXCHANGEABLE ON AND AFTER A DATE SPECIFIED THEREIN.

                                  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 SECURITY

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

                       PUBLIC SERVICE COMPANY OF COLORADO
                   First Collateral Trust Bond, Series No. 15

         Original Interest Accrual Date          September 9, 2003
                         Interest Rate:          5.50%
                       Stated Maturity:          April 1, 2014
                Interest Payment Dates:          April 1 and October 1
                  Regular Record Dates:          March 15 and September 15

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

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

Principal Amount                                               Registered No.
$                                                              CUSIP 744448 BX 8

         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 April 1, 2004, 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

                                  EXHIBIT B-1

<PAGE>

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.

         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 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 the Independent Investment Banker as having a maturity comparable to
the remaining term of the Securities of Series No. 15 that would be utilized, at
the time of selection and in accordance with customary

                                  EXHIBIT B-2

<PAGE>

financial practice, in pricing new issues of corporate debt securities of
comparable maturity to the remaining term of the Securities of Series No. 15.

         "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., McDonald Investments Inc. or UBS Securities LLC and any other Primary
Treasury Dealer designated by, and not affiliated with, Banc One Capital
Markets, Inc., McDonald Investments Inc. or UBS Securities LLC and their
respective successors, provided, however, that if any of the foregoing or any of
its 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 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

                                  EXHIBIT B-3

<PAGE>

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.

         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

                                  EXHIBIT B-4

<PAGE>

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 B-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.

         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

                                  EXHIBIT B-6

<PAGE>

SECURITIES DEPOSITARY WITH RESPECT TO THE SECURITIES; OR (B) THE COMPANY SHALL
HAVE DELIVERED TO THE TRUSTEE A COMPANY ORDER TO THE EFFECT THAT THE SECURITIES
SHALL BE SO EXCHANGEABLE ON AND AFTER A DATE SPECIFIED THEREIN.

                                  EXHIBIT B-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 B-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        None
August 15, 2002            Series No. 7            $ 48,750,000    $ 48,750,000
September 1, 2002          Series No. 8            $600,000,000        None
September 15, 2002         Series No. 9            $530,000,000        None
April 1, 2003              Series No. 10           $600,000,000    $600,000,000
March 1, 2003              Series No. 11           $250,000,000    $250,000,000
May 1, 2003                Series No. 13           $350,000,000    $350,000,000
</TABLE>

                                  SCHEDULE A-1

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