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                                Guarantee Agreement

                                       between

                          PUBLIC SERVICE COMPANY OF COLORADO
                                    (as Guarantor)

                                         and

                                 The Bank of New York
                           (as Preferred Guarantee Trustee)




                                     Dated as of

                                   __________, 1998


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                                  TABLE OF CONTENTS


                                                                                 Page
                                                                                 ----
                                                                              
ARTICLE I  DEFINITIONS
     SECTION 1.01.  Definitions. . . . . . . . . . . . . . . . . . . . . . . . . . .2

ARTICLE II   TRUST INDENTURE ACT
     SECTION 2.01.  Trust Indenture Act; Application . . . . . . . . . . . . . . . .4
     SECTION 2.02.  List of Holders. . . . . . . . . . . . . . . . . . . . . . . . .4
     SECTION 2.03.  Reports by the Preferred Guarantee Trustee . . . . . . . . . . .4
     SECTION 2.04.  Periodic Reports to Preferred Guarantee Trustee. . . . . . . . .4
     SECTION 2.05.  Evidence of Compliance with Conditions Precedent . . . . . . . .5
     SECTION 2.06.  Events of Default; Waiver. . . . . . . . . . . . . . . . . . . .5
     SECTION 2.07.  Event of Default; Notice . . . . . . . . . . . . . . . . . . . .5
     SECTION 2.08.  Conflicting Interests. . . . . . . . . . . . . . . . . . . . . .6

ARTICLE III  POWERS, DUTIES AND RIGHTS OF THE PREFERRED GUARANTEE TRUSTEE
     SECTION 3.01.  Powers and Duties of the Preferred Guarantee Trustee . . . . . .6
     SECTION 3.02.  Certain Rights of Preferred Guarantee Trustee. . . . . . . . . .7

ARTICLE IV   PREFERRED GUARANTEE TRUSTEE
     SECTION 4.01.  Preferred Guarantee Trustee; Eligibility . . . . . . . . . . . .9
     SECTION 4.02.  Appointment, Removal and Resignation of the Preferred
                       Guarantee Trustee . . . . . . . . . . . . . . . . . . . . . 10

ARTICLE V    GUARANTEE
     SECTION 5.01.  Guarantee. . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     SECTION 5.02.  Waiver of Notice and Demand. . . . . . . . . . . . . . . . . . 11
     SECTION 5.03.  Obligations Not Affected . . . . . . . . . . . . . . . . . . . 11
     SECTION 5.04.  Rights of Holders. . . . . . . . . . . . . . . . . . . . . . . 12
     SECTION 5.05.  Guarantee of Payment . . . . . . . . . . . . . . . . . . . . . 12
     SECTION 5.06.  Subrogation. . . . . . . . . . . . . . . . . . . . . . . . . . 12
     SECTION 5.07.  Independent Obligations. . . . . . . . . . . . . . . . . . . . 13

ARTICLE VI   SUBORDINATION
     SECTION 6.01.  Ranking. . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     SECTION 6.02.  PARI PASSU Guarantees. . . . . . . . . . . . . . . . . . . . . 13

ARTICLE VII  TERMINATION
     SECTION 7.01.  Termination. . . . . . . . . . . . . . . . . . . . . . . . . . 13

                                       -i-



ARTICLE VIII INDEMNIFICATION
     SECTION 8.01.  Exculpation. . . . . . . . . . . . . . . . . . . . . . . . . . 13
     SECTION 8.02.  Indemnification. . . . . . . . . . . . . . . . . . . . . . . . 14

ARTICLE IX   MISCELLANEOUS
     SECTION 9.01.  Successors and Assigns . . . . . . . . . . . . . . . . . . . . 14
     SECTION 9.02.  Amendments . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     SECTION 9.03.  Notices. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     SECTION 9.04.  Benefit. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     SECTION 9.05.  Interpretation . . . . . . . . . . . . . . . . . . . . . . . . 16
     SECTION 9.06.  Governing Law. . . . . . . . . . . . . . . . . . . . . . . . . 16



                                       -ii-



                                CROSS-REFERENCE TABLE*



Section of                                                       Section of  
Trust Indenture Act                                              Guarantee of
1939, as amended                                                 Agreement   
- -------------------                                              ------------
                                                              
310(a).........................................................         4.01(a)
310(b).........................................................   4.01(c), 2.08
310(c).........................................................    Inapplicable
311(a).........................................................         2.02(b)
311(b).........................................................         2.02(b)
311(c).........................................................    Inapplicable
312(a).........................................................         2.02(a)
312(b).........................................................         2.02(b)
313............................................................            2.03
314(a).........................................................            2.04
314(b).........................................................    Inapplicable
314(c).........................................................            2.05
314(d).........................................................    Inapplicable
314(e).........................................................1.01, 2.05, 3.02
314(f).........................................................      2.01, 3.02
315(a).........................................................         3.01(d)
315(b).........................................................            2.07
315(c).........................................................            3.01
315(d).........................................................         3.01(d)
316(a).........................................................1.01, 2.06, 5.04
316(b).........................................................            5.03
316(c).........................................................            8.02
317(a).........................................................    Inapplicable
317(b).........................................................    Inapplicable
318(a).........................................................         2.01(b)
318(b).........................................................            2.01
318(c).........................................................         2.01(a)

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

*    This Cross-Reference Table does not constitute part of the Guarantee
     Agreement and shall not affect the interpretation of any of its terms or
     provisions.

                                       -iii-



                                 GUARANTEE AGREEMENT

     This GUARANTEE AGREEMENT (the "Preferred Securities Guarantee"), dated 
as of __________, 1998, is executed and delivered by Public Service Company 
of Colorado, a Colorado corporation (the "Guarantor"), to The Bank of New 
York, as trustee (the "Preferred Guarantee Trustee"), for the benefit of the 
Holders (as defined herein) from time to time of the Preferred Securities (as 
defined herein) of PSCO Capital Trust I, a Delaware statutory business trust 
(the "Issuer").

     WHEREAS, pursuant to an Amended and Restated Declaration of Trust (the 
"Declaration"), dated as of __________, 1998 among the Trustees named 
therein, the Guarantor, as Depositor, and the Holders from time to time of 
undivided beneficial interests in the assets of the Issuer, the Issuer is 
issuing $___________ aggregate liquidation amount of its ___% Trust Originated 
Preferred Securities (liquidation amount of $[     ] per preferred security) 
(the "Preferred Securities") representing undivided beneficial interests in 
the assets of the Issuer and having the terms set forth in the Declaration;

     WHEREAS, the Preferred Securities will be issued by the Issuer and the 
proceeds thereof, together with the proceeds from the sale by the Issuer of 
its Common Securities, will be used to purchase the Debentures (as defined in 
the Declaration) of the Guarantor which will be deposited with The Bank of 
New York, as Property Trustee under the Declaration, as Trust Property (as 
defined in the Declaration);

     WHEREAS, as incentive for the Holders to purchase Preferred Securities, 
the Guarantor desires irrevocably and unconditionally to agree, to the extent 
set forth herein, to pay to the Holders of the Preferred Securities the 
Guarantee Payments (as defined herein) and to make certain other payments on 
the terms and conditions set forth herein; and

     WHEREAS, the Guarantor is also executing and delivering a guarantee 
agreement (the "Common Securities Guarantee") in substantially identical 
terms to this Preferred Securities Guarantee for the benefit of the holders 
of the Common Securities (as defined herein), except that if an event of 
default (as defined in the Indenture) has occurred and is continuing, the 
Guarantee Payments under the Common Securities Guarantee are subordinated to 
the rights of Holders of Preferred Securities to receive Guarantee Payments 
under this Preferred Securities Guarantee.

     NOW, THEREFORE, in consideration of the purchase by each Holder of 
Preferred Securities, which purchase the Guarantor hereby agrees shall 
benefit the Guarantor, the Guarantor executes and delivers this Preferred 
Securities Guarantee for the benefit of the Holders from time to time of the 
Preferred Securities. 



                                      ARTICLE I

                                     DEFINITIONS

     SECTION 1.01.  Definitions.  As used in this Preferred Securities 
Guarantee, each of the terms set forth below shall, unless the context 
otherwise requires, have the following meaning. Each capitalized or otherwise 
defined term used but not otherwise defined herein shall have the meaning 
assigned to such terms in the Declaration as in effect on the date hereof.

     "Affiliate" of any specified Person means any other Person directly or 
indirectly controlling or controlled by or under direct or indirect common 
control with such specified Person. For the purposes of this definition, 
"control" when used with respect to any specified Person means the power to 
direct the management and policies of such Person, directly or indirectly, 
whether through the ownership of voting securities, by contract or otherwise; 
and the terms "controlling" and "controlled" have meanings correlative to the 
foregoing.

     "Common Securities" means the common securities representing undivided 
beneficial interests in the assets of the Issuer and having the rights 
provided therefor in the Declaration.

     "Covered Person" means any Holder or beneficial owner of Preferred 
Securities.

     "Event of Default" shall have the meaning specified in Section 2.06 (a).

     "Guarantee Payments" means the following payments, without duplication, 
with respect to the Preferred Securities, to the extent not paid or made by 
or on behalf of the Issuer pursuant to the Declaration or by the Guarantor 
pursuant to the Indenture: (i) any accumulated and unpaid Distributions 
required to be paid on the Preferred Securities, to the extent the Issuer 
shall have funds available therefor, (ii) the redemption price (the 
"Redemption Price") and all accrued and unpaid Distributions to the date of 
redemption to the extent the Issuer shall have funds available therefor, and 
(iii) upon a voluntary or involuntary dissolution and liquidation of the 
Issuer (other than in connection with a Distribution of Debentures to Holders 
of such Preferred Securities or the redemption of all such Preferred 
Securities), the lesser of (a) the aggregate of the liquidation amount of 
$[      ] per Preferred Security plus all accrued and unpaid Distributions on 
the Preferred Securities to the date of payment, to the extent the Issuer 
shall have funds available therefor and (b) the amount of assets of the 
Issuer remaining available for Distribution to Holders of Preferred 
Securities upon a dissolution and liquidation of the Issuer (in either case, 
the "Liquidation Distribution").  If an event of default under the Indenture 
has occurred and is continuing, the rights of holders of the Common 
Securities to receive payments under the Common Securities Guarantee are 
subordinated to the rights of Holders of Preferred Securities to receive 
Guarantee Payments.

     "Holder" means a Person in whose name a Preferred Security is registered 
in the Securities Register; provided, however, that in determining whether 
the holders of the requisite percentage of Preferred Securities have given 
any request, notice, consent or waiver hereunder, "Holder" 

                                       -2-



shall not include the Guarantor, the Preferred Guarantee Trustee or any 
Affiliate of the Guarantor or the Preferred Guarantee Trustee.

     "Indemnified Person" means the Preferred Guarantee Trustee, any 
Affiliate of the Preferred Guarantee Trustee, or any officers, directors, 
shareholders, members, partners, employees, representatives, nominees, 
custodians or agents of the Preferred Guarantee Trustee.

     "Indenture" means the Indenture dated as of _________, 1998, as amended 
or supplemented from time to time, between Public Service Company of Colorado 
and The Bank of New York, as trustee thereunder. 

     "List of Holders" has the meaning specified in Section 2.02(a). 

     "Majority in liquidation amount of the Preferred Securities" means, 
except as provided by the Trust Indenture Act, a vote by the Holders of more 
than 50% of the aggregate liquidation amount of all then outstanding 
Preferred Securities issued by the Issuer.

     "Officers' Certificate" means a certificate signed by the Chairman, the 
President, or any Senior or Executive Vice President and the Treasurer, any 
Assistant Treasurer, the Secretary or any Assistant Secretary of the 
Guarantor.

     "Person" means any individual, corporation, partnership, limited 
liability company, joint venture, association, joint-stock company, trust, 
unincorporated organization, government or any agency or political 
subdivision thereof or any other entity.

     "Preferred Guarantee Trustee" means The Bank of New York, until a 
Successor Preferred Guarantee Trustee (as defined below) has been appointed 
and has accepted such appointment pursuant to the terms of this Preferred 
Securities Guarantee and thereafter means each such Successor Preferred 
Guarantee Trustee.

     "Responsible Officer" means, with respect to the Preferred Guarantee 
Trustee, any Vice President, any Assistant Vice President, any Trust Officer 
or Assistant Trust Officer or any other officer of the Corporate Trust 
Department of the Guarantee Trustee customarily performing functions similar 
to those performed by any of the above designated officers and also means, 
with respect to a particular corporate trust matter, any other officer to 
whom such matter is referred because of that officer's knowledge of and 
familiarity with the particular subject.

     "Successor Preferred Guarantee Trustee" means a successor Preferred 
Guarantee Trustee possessing the qualifications to act as Preferred Guarantee 
Trustee under Section 4.01. 

     "Trust Indenture Act" means the Trust Indenture Act of 1939 as in force at
the date as of which this instrument was executed; provided, however, that in
the event the Trust Indenture Act 

                                       -3-



of 1939 is amended after such date, "Trust Indenture Act" means, to the 
extent required by any such amendment, the Trust Indenture Act of 1939, as so 
amended.

                                      ARTICLE II

                                 TRUST INDENTURE ACT

     SECTION 2.01.  Trust Indenture Act; Application.

     (a)  This Preferred Securities Guarantee is subject to the provisions of 
the Trust Indenture Act that are required to be part of this Preferred 
Securities Guarantee and shall, to the extent applicable, be governed by such 
provisions. 

     (b)  If, and to the extent that any provision of this Preferred 
Securities Guarantee limits, qualifies or conflicts with the duties imposed 
by Sections 310 to 317, inclusive, of the Trust Indenture Act, such imposed 
duties shall control. 

     SECTION 2.02.  List of Holders.

     (a)  The Guarantor shall furnish or cause to be furnished to the 
Preferred Guarantee Trustee (i) semiannually, on or before January 15 and 
July 15 of each year, a list, in such form as the Preferred Guarantee Trustee 
may reasonably require, of the names and addresses of the Holders ("List of 
Holders") as of a date not more than 15 days prior to the delivery thereof, 
and (ii) at such other times as the Preferred Guarantee Trustee may request in 
writing, within 30 days after the receipt by the Guarantor of any such 
request, a List of Holders as of a date not more than 15 days prior to the 
time such list is furnished, in each case to the extent such information is 
in the possession or control of the Guarantor and is not identical to a 
previously supplied List of Holders or has not otherwise been received by the 
Preferred Guarantee Trustee in its capacity as such. The Preferred Guarantee 
Trustee may destroy any List of Holders previously given to it on receipt of 
a new List of Holders.

     (b)  The Preferred Guarantee Trustee shall comply with its obligations 
under Sections 311(a), Section 311(b) and Section 312(b) of the Trust 
Indenture Act. 

     SECTION 2.03.  Reports by the Preferred Guarantee Trustee.  Within 60 
days after May 31 of each year, the Preferred Guarantee Trustee shall provide 
to the Holders such reports as are required by Section 313 of the Trust 
Indenture Act, if any, in the form and in the manner provided by Section 313 
of the Trust Indenture Act.  The Preferred Guarantee Trustee shall also 
comply with the requirements of Section 313(d) of the Trust Indenture Act.

     SECTION 2.04.  Periodic Reports to Preferred Guarantee Trustee.  The 
Guarantor shall provide to the Preferred Guarantee Trustee, the Securities 
and Exchange Commission and the Holders such documents, reports and 
information, if any, as required by Section 314 of the Trust Indenture Act 
and the compliance certificate required by Section 314 of the Trust Indenture 
Act in the form and manner and at the times required by Section 314 of the 
Trust Indenture Act.

                                       -4-



     SECTION 2.05.  Evidence of Compliance with Conditions Precedent.  The
Guarantor shall provide to the Preferred Guarantee Trustee such evidence of
compliance with such conditions precedent, if any, provided for in this
Preferred Securities Guarantee that relate to any of the matters set forth in
Section 314(c) of the Trust Indenture Act.  Each Officers' Certificate and
Opinion of Counsel delivered with respect to compliance with a condition or
covenant provided for in this Preferred Securities Guarantee shall include:

          (a)  a statement that each officer signing the Officers' Certificate
     or Opinion of Counsel has read the covenant or condition and the definition
     relating thereto;

          (b)  a brief statement of the nature and scope of the examination or
     investigation undertaken by each officer in rendering the Officers'
     Certificate or Opinion of Counsel and upon which the statements contained
     therein are based;

          (c)  a statement that each such officer has made such examination or
     investigation as, in such officer's opinion, is necessary to enable such
     officer to express an informed opinion as to whether or not such covenant
     or condition has been complied with; and

          (d)  a statement as to whether, in the opinion of each such officer,
     such condition or covenant has been complied with.

     SECTION 2.06.  Events of Default; Waiver.  

     (a)  An Event of Default means a default by the Guarantor on any of its 
payment or other obligations under this Preferred Securities Guarantee; 
provided, that except with respect to a default resulting from a failure to 
pay any Guarantee Payment, the Guarantor shall have received notice of such 
default and shall not have cured such default within 60 days after receipt of 
such notice.

     (b)   The Holders of a Majority in liquidation amount of the Preferred 
Securities may, by vote, on behalf of the Holders, waive any past Event of 
Default and its consequences. Upon such waiver, any such Event of Default 
shall cease to exist, and any Event of Default arising therefrom shall be 
deemed to have been cured, for every purpose of this Preferred Securities 
Guarantee, but no such waiver shall extend to any subsequent or other default 
or Event of Default or impair any right consequent therefrom. 

     SECTION 2.07.  Event of Default; Notice.

     (a)  The Preferred Guarantee Trustee shall, within 90 days after the
occurrence of an Event of Default, transmit by mail, first class postage
prepaid, to the Holders, notices of all Events of Default known to the Preferred
Guarantee Trustee, unless such defaults have been cured before the giving of
such notice, provided, that, except in the case of a default in the payment of a
Guarantee Payment, the Preferred Guarantee Trustee shall be protected in
withholding such notice if and so long as the Board of Directors, the executive
committee or a trust committee of 

                                       -5-



directors and/or Responsible Officers of the Preferred Guarantee Trustee in 
good faith determines that the withholding of such notice is in the interests 
of the Holders.

     (b)  The Preferred Guarantee Trustee shall not be deemed to have 
knowledge of any Event of Default unless the Preferred Guarantee Trustee 
shall have received written notice, or a Responsible Officer charged with the 
administration of the Declaration shall have obtained written notice, of such 
Event of Default.

     SECTION 2.08.  Conflicting Interests.  The Declaration shall be deemed 
to be specifically described in this Preferred Securities Guarantee for the 
purposes of clause (i) of the first proviso contained in Section 310(b) of 
the Trust Indenture Act.

                                     ARTICLE III

                           POWERS, DUTIES AND RIGHTS OF THE
                             PREFERRED GUARANTEE TRUSTEE

     SECTION 3.01.  Powers and Duties of the Preferred Guarantee Trustee. 

     (a)  This Preferred Securities Guarantee shall be held by the Preferred 
Guarantee Trustee for the benefit of the Holders, and the Preferred Guarantee 
Trustee shall not transfer this Preferred Securities Guarantee to any Person 
except a Holder exercising his or her rights pursuant to Section 5.04(iv) or 
to a Successor Preferred Guarantee Trustee on acceptance by such Successor 
Preferred Guarantee Trustee of its appointment to act as Successor Preferred 
Guarantee Trustee.  The right, title and interest of the Preferred Guarantee 
Trustee shall automatically vest in any Successor Preferred Guarantee Trustee 
upon acceptance by such Successor Preferred Guarantee Trustee of its 
appointment hereunder and such vesting and cessation of title shall be 
effective whether or not conveyancing documents have been executed and 
delivered pursuant to the appointment of such Successor Preferred Guarantee 
Trustee.

     (b)  If an Event of Default has occurred and is continuing, the 
Preferred Guarantee Trustee shall enforce this Preferred Securities Guarantee 
for the benefit of the Holders. 

     (c)  The Preferred Guarantee Trustee, before the occurrence of any Event 
of Default and after the curing of all Events of Default that may have 
occurred, shall undertake to perform only such duties as are specifically set 
forth in this Preferred Securities Guarantee, and no implied covenants shall 
be read into this Preferred Securities Guarantee against the Preferred 
Guarantee Trustee.  In case an Event of Default has occurred and is 
continuing (and has not been cured or waived pursuant to Section 2.06), the 
Preferred Guarantee Trustee shall exercise such of the rights and powers 
vested in it by this Preferred Securities Guarantee, and use the same degree 
of care and skill in its exercise thereof, as a prudent person would exercise 
or use in the conduct of his or her own affairs.

                                       -6-



     (d)  No provision of this Preferred Securities Guarantee shall be 
construed to relieve the Preferred Guarantee Trustee from liability for its 
own negligent action, its own negligent failure to act or its own willful 
misconduct, except that: 

          (i)  prior to the occurrence of any Event of Default and after the
     curing or waiving of all such Events of Default that may have occurred: 

               (A)  the duties and obligations of the Preferred Guarantee
          Trustee shall be determined solely by the express  provisions of this
          Preferred Securities Guarantee, and the Preferred Guarantee Trustee
          shall not be liable except for the performance of such duties and
          obligations as are specifically set forth in this Preferred Securities
          Guarantee, and no implied covenants or obligations shall be read into
          this Preferred Securities Guarantee against the Preferred Guarantee
          Trustee; and


               (B)  in the absence of bad faith on the part of the Preferred
          Guarantee Trustee, the Preferred Guarantee Trustee may conclusively
          rely, as to the truth of the statements and the correctness of the
          opinions expressed therein, upon any certificates or opinions
          furnished to the Preferred Guarantee Trustee and conforming to the 
          requirements of this Preferred Securities Guarantee; but in the case
          of any such certificates or opinions that by any provision hereof or
          of the Trust Indenture Act are specifically required to be furnished
          to the Preferred Guarantee Trustee, the Preferred Guarantee Trustee
          shall be under a duty to examine the same to determine whether or not
          they conform to the requirements of this Preferred Securities
          Guarantee;

          (ii) the Preferred Guarantee Trustee shall not be liable for any error
     of judgment made in good faith by a Responsible Officer of the Preferred
     Guarantee Trustee, unless it shall be proved that the Preferred Guarantee
     Trustee was negligent in ascertaining the pertinent facts upon which such
     judgment was made;

          (iii)     the Preferred Guarantee Trustee shall not be liable with
     respect to any action taken or omitted to be taken by it in good faith in
     accordance with the direction of the Holders of a Majority in liquidation
     amount of the Preferred Securities relating to the time, method and place
     of conducting any proceeding for any remedy available to the Preferred
     Guarantee Trustee, or exercising any trust or power conferred upon the
     Preferred Guarantee Trustee under this Preferred Securities Guarantee; and

          (iv) no provision of this Preferred Securities Guarantee shall require
     the Preferred Guarantee Trustee to expend or risk its own funds or
     otherwise incur personal financial liability in the performance of any of
     its duties or in the exercise of any of its rights or powers, if the
     Preferred Guarantee Trustee shall have reasonable grounds for believing
     that the repayment of such funds or liability is not reasonably assured to
     it under the terms of this Preferred Securities Guarantee or reasonable
     indemnity against such risk or liability is not reasonably assured to it.

                                       -7-



     SECTION 3.02.  Certain Rights of Preferred Guarantee Trustee.

     (a)  Subject to the provisions of Section 3.01:

          (i)  The Preferred Guarantee Trustee may rely and shall be fully
     protected in acting or refraining from acting upon any resolution, 
     certificate, statement,  instrument,  opinion, report, notice, request,
     direction, consent, order, bond, debenture, note, other evidence of
     indebtedness or other paper or document believed by it to be genuine and to
     have been signed, sent or presented by the proper party or parties. 

          (ii) Any direction or act of the Guarantor contemplated by this
     Preferred Securities Guarantee shall be sufficiently evidenced by an
     Officers' Certificate unless otherwise prescribed herein.

          (iii)     Whenever, in the administration of this Preferred Securities
     Guarantee, the Preferred Guarantee Trustee shall deem it desirable that a
     matter be proved or established before taking, suffering or omitting to
     take any action hereunder, the Preferred Guarantee Trustee (unless other
     evidence is herein specifically prescribed) may, in the absence of bad
     faith on its part, request and rely upon an Officers' Certificate which,
     upon receipt of such request from the Preferred Guarantee Trustee, shall be
     promptly delivered by the Guarantor.

          (iv) The Preferred Guarantee Trustee may consult with legal counsel,
     and the written advice or Opinion of Counsel with respect to legal matters
     shall be full and complete authorization and protection in respect of any
     action taken, suffered or omitted to be taken by it hereunder in good faith
     and in accordance with such advice or opinion. Such legal counsel may be
     legal counsel to the Guarantor or any of its Affiliates and may be one of
     its employees.  The Preferred Guarantee Trustee shall have the right at any
     time to seek instructions concerning the administration of this Preferred
     Securities Guarantee from any court of competent jurisdiction.

          (v)  The Preferred Guarantee Trustee shall be under no obligation to
     exercise any of the rights or powers vested in it by this Preferred
     Securities Guarantee at the request or direction of any Holder, unless such
     Holder shall have provided to the Preferred Guarantee Trustee such
     reasonable indemnity as would satisfy a reasonable person in the position
     of the Preferred Guarantee Trustee, against the costs, expenses (including
     attorneys' fees and expenses) and liabilities that might be incurred by it
     in complying with such request or direction; provided that, nothing
     contained in this Section 3.02(a)(v) shall be taken to relieve the
     Preferred Guarantee Trustee, upon the occurrence of an Event of Default, of
     its obligation to exercise the rights and powers vested in it by this
     Preferred Securities Guarantee.

          (vi) The Preferred Guarantee Trustee shall not be bound to make any
     investigation  into the facts or matters stated in any resolution,
     certificate, statement, instrument, opinion, report, notice, request,
     direction, consent, order, bond, debenture, 

                                       -8-



     note, other evidence of indebtedness or other paper or document, but the 
     Preferred Guarantee Trustee, in its discretion, may make such further 
     inquiry or investigation into such facts or matters as it may see fit.

          (vii)     The Preferred Guarantee Trustee may execute any of the
     trusts or powers hereunder or perform any duties hereunder either directly
     or by or through its agents or attorneys, and the Preferred Guarantee
     Trustee shall not be responsible for any misconduct or negligence on the
     part of any such agent or attorney appointed with due care by it hereunder.

          (viii)    Any action taken by the Preferred Guarantee Trustee or its
     agents hereunder shall bind the Holders of the Preferred Securities, and
     the signature of the Preferred Guarantee Trustee or its agents alone shall
     be sufficient and effective to perform any such action.  No third party
     shall be required to inquire as to the authority of the Preferred Guarantee
     Trustee to so act or as to its compliance with any of the terms and
     provisions of this Preferred Securities Guarantee, both of which shall be
     conclusively evidenced by the Preferred Guarantee Trustee's or its agent's
     taking such action.

          (ix) Whenever in the administration of this Preferred Securities
     Guarantee the Preferred Guarantee Trustee shall deem it desirable to
     receive instructions with respect to enforcing any remedy or right or
     taking any other action hereunder, the Preferred Guarantee Trustee (A) may
     request instructions from the Holders, (B) may refrain from enforcing such
     remedy or right or taking such other action until such instructions are
     received, and (C) shall be protected in acting in accordance with such
     instructions. 

     (b)  No provision of this Preferred Securities Guarantee shall be deemed 
to impose any duty or obligation on the Preferred Guarantee Trustee to 
perform any act or acts or exercise any right, power, duty or obligation 
conferred or imposed on it in any jurisdiction in which it shall be illegal, 
or in which the Preferred Guarantee Trustee shall be unqualified or 
incompetent in accordance with applicable law, to perform any such act or 
acts or to exercise any such right, power, duty or obligation.  No permissive 
power or authority available to the Preferred Guarantee Trustee shall be 
construed to be a duty to act in accordance with such power and authority.

                                      ARTICLE IV

                              PREFERRED GUARANTEE TRUSTEE

     SECTION 4.01.  Preferred Guarantee Trustee; Eligibility.

     (a)  There shall at all times be a Preferred Guarantee Trustee which shall:

          (i)  not be an Affiliate of the Guarantor; and

          (ii) be a Person that is eligible pursuant to the Trust Indenture Act
     to act as such and has a combined capital and surplus of at least fifty
     million U.S. dollars 

                                       -9-



     ($50,000,000), and shall be a corporation meeting the requirements of 
     Section 310(a) of the Trust Indenture Act.  If such corporation publishes 
     reports of condition at least annually, pursuant to law or to the 
     requirements of the supervising or examining authority, then, for the 
     purposes of this Section and to the extent permitted by the Trust Indenture
     Act, the combined capital and surplus of such corporation shall be deemed 
     to be its combined capital and surplus as set forth in its most recent 
     report of condition so published.

     (b)  If at any time the Preferred Guarantee Trustee shall cease to be 
eligible to so act under Section 4.01(a), the Preferred Guarantee Trustee 
shall immediately resign in the manner and with the effect set out in Section 
4.02(c).

     (c)  If the Preferred Guarantee Trustee has or shall acquire any 
"conflicting interest" within the meaning of Section 310(b) of the Trust 
Indenture Act, the Preferred Guarantee Trustee and Guarantor shall in all 
respects comply with the provisions of Section 310(b) of the Trust Indenture 
Act.  In determining whether the Preferred Guarantee Trustee has a 
"conflicting interest" within the meaning of Section 310(b)(1) of the Trust 
Indenture Act, the provisions contained in the proviso to Section 310(b)(1) 
of the Trust Indenture Act and the Preferred Guarantee Trustee's Statement of 
Eligibility on Form T-1 shall be deemed incorporated herein. 

     SECTION 4.02.  Appointment, Removal and Resignation of the Preferred 
Guarantee Trustee.

     (a)  Subject to Section 4.02(b), the Preferred Guarantee Trustee may be 
appointed or removed without cause at any time by the Guarantor.

     (b)  The Preferred Guarantee Trustee shall not be removed until a new, 
eligible Preferred Guarantee Trustee has been appointed (a "Successor 
Preferred Guarantee Trustee") and has accepted such appointment and assumed 
the applicable obligations hereunder by written instrument executed by such 
Successor Preferred Guarantee Trustee and delivered to the Guarantor.

     (c)  The Preferred Guarantee Trustee may resign from office (without 
need for prior or subsequent accounting) by an instrument in writing executed 
by the Preferred Guarantee Trustee and delivered to the Guarantor, which 
resignation shall not take effect until a Successor Preferred Guarantee 
Trustee has been appointed and has accepted such appointment by instrument in 
writing executed by such Successor Preferred Guarantee Trustee and delivered 
to the Guarantor and the resigning Preferred Guarantee Trustee. 

     (d)  If no Successor Preferred Guarantee Trustee shall have been 
appointed and accepted appointment as provided in this Section 4.02 within 60 
days after delivery to the Guarantor of an instrument of resignation, the 
resigning Preferred Guarantee Trustee may petition, at the expense of the 
Guarantor, any court of competent jurisdiction for appointment of a Successor 
Preferred Guarantee Trustee.  Such court may thereupon, after prescribing 
such notice, if any, as it may deem proper, appoint a Successor Preferred 
Guarantee Trustee.

                                       -10-



                                      ARTICLE V

                                      GUARANTEE

     SECTION 5.01.  Guarantee.  The Guarantor irrevocably and unconditionally 
agrees to pay in full to the Holders of the Outstanding Preferred Securities 
the Guarantee Payments (without duplication of amounts theretofore paid by or 
on behalf of the Issuer pursuant to the Declaration or by the Guarantor 
pursuant to the Indenture), as and when due, regardless of any defense, right 
of set-off or counterclaim which the Issuer may have or assert.  The 
Guarantor's obligation to make a Guarantee Payment may be satisfied by direct 
payment of the required amounts by the Guarantor to the Holders or by causing 
the Issuer to pay such amounts to the Holders.

     SECTION 5.02.  Waiver of Notice and Demand.  The Guarantor hereby waives 
notice of acceptance of the Preferred Securities Guarantee and of any 
liability to which it applies or may apply, presentment, demand for payment, 
any right to require a proceeding first against the Preferred Guarantee 
Trustee, the Issuer or any other Person before proceeding against the 
Guarantor, protest, notice of nonpayment, notice of dishonor, notice of 
redemption and all other notices and demands. 

     SECTION 5.03.  Obligations Not Affected.  The obligations,  covenants, 
agreements and duties of the Guarantor under this Preferred Securities 
Guarantee shall in no way be affected or impaired by reason of the happening 
from time to time of any of the following:

     (a)  the release or waiver, by operation of law or otherwise, of the 
performance or observance by the Issuer of any express or implied agreement, 
covenant, term or condition relating to the Preferred Securities to be 
performed or observed by the Issuer;

     (b)  the extension of time for the payment by the Issuer of all or any 
portion of the Distributions (other than an extension of time for payment of 
Distributions that results from an Extension Period on the Debentures as so 
provided in the Indenture), Redemption Price, Liquidation Distribution or any 
other sums payable under the terms of the Preferred Securities or the 
extension of time for the performance of any other obligation under, arising 
out of, or in connection with, the Preferred Securities; 

     (c)  any failure, omission, delay or lack of diligence on the part of 
the Holders to enforce, assert or exercise any right, privilege, power or 
remedy conferred on the Holders pursuant to the terms of the Preferred 
Securities, or any action on the part of the Issuer granting indulgence or 
extension of any kind;

     (d)  the voluntary or involuntary liquidation, dissolution, sale of any 
collateral, receivership,  insolvency, bankruptcy, assignment for the benefit 
of creditors,  reorganization,  arrangement,  composition  or readjustment of 
debt of, or other similar proceedings affecting, the Issuer or any of the 
assets of the Issuer;

                                       -11-



     (e)  any invalidity of, or detect or deficiency in, the Preferred 
Securities;

     (f)  the settlement or compromise of any obligation guaranteed hereby or 
hereby incurred; or

     (g)  to the extent permitted by law, any other circumstance whatsoever 
that might otherwise constitute a legal or equitable discharge or defense of 
a guarantor, it being the intent of this Section 5.03 that the obligations of 
the Guarantor hereunder shall be absolute and unconditional under any and all 
circumstances.

     There shall be no obligation of the Holders to give notice to, or obtain 
the consent of, the Guarantor with respect to the happening of any of the 
foregoing.

     SECTION 5.04.  Rights of Holders.  The Guarantor expressly acknowledges 
that:  (i) this Preferred Securities Guarantee will be deposited with the 
Preferred Guarantee Trustee to be held for the benefit of the Holders; (ii) 
the Preferred Guarantee Trustee has the right to enforce this Preferred 
Securities Guarantee on behalf of the Holders; (iii) the Holders of a 
Majority in liquidation amount of the Preferred Securities have the right to 
direct the time, method and place of conducting any proceeding for any remedy 
available to the Preferred Guarantee Trustee in respect of this Preferred 
Securities Guarantee or exercise or direct the exercise of any trust or power 
conferred upon the Preferred Guarantee Trustee under this Preferred 
Securities Guarantee; and (iv) any Holder may institute a legal proceeding 
directly against the Guarantor to enforce its rights under this Preferred 
Securities Guarantee, without first instituting a legal proceeding against 
the Preferred Guarantee Trustee, the Issuer or any other Person.

     SECTION 5.05.  Guarantee of Payment.  This Preferred Securities 
Guarantee creates a guarantee of payment and not of collection (i.e., the 
guaranteed party may institute a legal proceeding directly against the 
Guarantor to enforce its rights under the Preferred Securities Guarantee 
without first instituting a legal proceeding against any other person or 
entity).  This Preferred Securities Guarantee will not be discharged except 
by payment of the Guarantee Payments in full to the extent not previously 
paid or upon Distribution to the Holders of the Preferred Securities of the 
corresponding series of Debentures as provided in the Declaration.

     SECTION 5.06.  Subrogation.  The Guarantor shall be subrogated to all 
(if any) rights of the Holders against the Issuer in respect of any amounts 
paid to the Holders by the Guarantor under this Preferred Securities 
Guarantee and shall have the right to waive payment by the Issuer pursuant to 
Section 5.01; provided, however, that the Guarantor shall not (except to the 
extent required by mandatory provisions of law) be entitled to enforce or 
exercise any rights which it may acquire by way of subrogation or any 
indemnity, reimbursement or other agreement, in all cases as a result of 
payment under this Preferred Securities Guarantee, if, at the time of any 
such payment, any amounts are due and unpaid under this Preferred Securities 
Guarantee.  If any amount shall be paid to the Guarantor in violation of the 
preceding sentence, the Guarantor agrees to hold such amount in trust for the 
Holders and to pay over such amount to the Holders.

                                       -12-



     SECTION 5.07.  Independent Obligations.  The Guarantor acknowledges that 
its obligations hereunder are independent of the obligations of the Issuer 
with respect to the Preferred Securities and that the Guarantor shall be 
liable as principal and as debtor hereunder to make Guarantee Payments 
pursuant to the terms of this Preferred Securities Guarantee notwithstanding 
the occurrence of any event referred to in subsections (a) through (g), 
inclusive, of Section 5.03 hereof. 

                                      ARTICLE VI

                                    SUBORDINATION

     SECTION 6.01.  Ranking.  This Preferred Securities Guarantee shall 
constitute an unsecured obligation of the Guarantor and shall rank (a) 
subordinate and junior in right of payment to all general liabilities of the 
Guarantor, (b) PARI PASSU with the senior most preferred stock now or 
hereafter issued by the Guarantor and with any guarantee now or hereafter 
issued by the Guarantor in respect of preferred stock of any affiliate of the 
Guarantor and (c) senior to the Guarantor's common stock. 

     SECTION 6.02.  PARI PASSU Guarantees.  This Preferred Securities 
Guarantee shall rank PARI PASSU with any similar Preferred Securities 
Guarantees issued by the Guarantor on behalf of the holders of trust 
preferred securities issued by other PSCO Trusts.

                                     ARTICLE VII

                                     TERMINATION

     SECTION 7.01.  Termination.  This Preferred Securities Guarantee shall 
terminate and be of no further force and effect upon full payment of the 
Redemption Price or Liquidation Distribution for the Preferred Securities or 
upon Distribution of the Debentures to the Holders of the Preferred 
Securities. This Preferred Securities Guarantee will continue to be effective 
or will be reinstated, as the case may be, if at any time any Holder of the 
Preferred Securities must restore payment of any sums paid under the 
Preferred Securities or this Preferred Securities Guarantee.

                                     ARTICLE VIII

                                   INDEMNIFICATION

     SECTION 8.01.  Exculpation.

     (a)  No Indemnified Person shall be liable, responsible or accountable 
in damages or otherwise to the Guarantor or any Covered Person for any loss, 
damage or claim incurred by reason of any act or omission performed or 
omitted by such Indemnified Person in good faith in accordance with this 
Preferred Securities Guarantee and in a manner that such Indemnified Person 
reasonably believed to be within the scope of the authority conferred on such 
Indemnified Person by this Preferred Securities Guarantee or by law, except 
that an Indemnified Person shall be liable 

                                       -13-




for any such loss, damage or claim incurred by reason of such Indemnified 
Person's negligence or willful misconduct with respect to such acts or 
omissions.

     (b)  An Indemnified Person shall be fully protected in relying in good 
faith upon the records of the Guarantor and upon such information, opinions, 
reports or statements presented to the Guarantor by any Person as to matters 
the Indemnified Person reasonably believes are within such other Person's 
professional or expert competence and who has been selected with reasonable 
care by or on behalf of the Guarantor, including information, opinions, 
reports or statements as to the value and amount of the assets, liabilities, 
profits, losses, or any other facts pertinent to the existence and amount of 
assets from which Distributions to Holders of Preferred Securities might 
properly be paid.

     SECTION 8.02.  Indemnification.

     (a)  To the fullest extent permitted by applicable law, the Guarantor 
shall indemnify and hold harmless each Indemnified Person from and against 
any loss, damage or claim incurred by such Indemnified Person by reason of 
any act or omission performed or omitted by such Indemnified Person in good 
faith in accordance with this Preferred Securities Guarantee and in a manner 
such Indemnified Person reasonably believed to be within the scope of 
authority conferred on such Indemnified Person by this Preferred Securities 
Guarantee, except that no Indemnified Person shall be entitled to be 
indemnified in respect of any loss, damage or claim incurred by such 
Indemnified Person by reason of negligence or willful misconduct with respect 
to such acts or omissions.

     (b)  To the fullest extent permitted by applicable law, reasonable 
expenses (including legal fees) incurred by an Indemnified Person in 
defending any claim, demand, action, suit or proceeding shall, from time to 
time, be advanced by the Guarantor prior to the final disposition of such 
claim, demand, action, suit or proceeding upon receipt by the Guarantor of an 
undertaking by or on behalf of the Indemnified Person to repay such amount if 
it shall be determined that the Indemnified Person is not entitled to be 
indemnified as authorized in Section 8.02(a).

     (c)  The obligation to indemnify as set forth in this Section 8.02 shall 
survive the termination of the Preferred Securities Guarantee.

                                      ARTICLE IX

                                    MISCELLANEOUS

     SECTION 9.01.  Successors and Assigns.  All guarantees and agreements 
contained in this Preferred Securities Guarantee shall bind the successors, 
assigns, receivers, trustees and representatives of the Guarantor and shall 
inure to the benefit of the Holders of the Preferred Securities then 
outstanding.  The Guarantor may not consolidate with or merge with or into, 
or sell, convey, transfer or lease its properties and assets as an entirety 
or substantially as an entirety (either in one transaction or a series of 
transactions) to, any Person unless permitted under Article Eight of the 
Indenture.  In connection with a consolidation, merger or sale involving the 

                                       -14-



Guarantor that is permitted under Article Eight of the Indenture the Person 
formed by or surviving  such consolidation or merger or to which such sale, 
conveyance, transfer or lease shall have been made, if other than the 
Guarantor, shall expressly assume all of the obligations of the Guarantor 
hereunder and under the Declaration.

     SECTION 9.02.  Amendments.  Except with respect to any changes which do 
not adversely affect the rights of the Holders in any material respect (in 
which case no consent of the Holders will be required), this Preferred 
Securities Guarantee may only be amended with the prior approval of the 
Holders of a Majority in liquidation amount of the Preferred Securities  
(excluding any Preferred Securities held by the Guarantor or an Affiliate 
thereof).  The provisions of Article VI of the Declaration concerning 
meetings of the Holders shall apply to the giving of such approval.

     SECTION 9.03.  Notices.  Any notice, request or other communication 
required or permitted to be given hereunder shall be in writing and 
delivered, telecopied or mailed by first class mail, postage prepaid, as 
follows:

          (a)  if given to the Guarantor, to the address set forth below or such
     other address as the Guarantor may give notice of to the Holders: 

          Public Service Company of Colorado
          1225 17th Street
          Denver, CO  80202-5533
          Facsimile No:  [         ]
          Attention:  [             ]

          (b)  if given to the Issuer, in care of the Preferred Guarantee
     Trustee, at the Issuer's (and the Preferred Guarantee Trustee's) address
     set forth below or such other address as the Preferred Guarantee Trustee on
     behalf of the Issuer may give notice to the Holders:

          PSCO Capital Trust I
          1225 17th Street
          Denver, CO  80202-5533
          Facsimile No:  [         ]
          Attention:  [             ]

     with a copy to:

          The Bank of New York
          101 Barclay Street, 21st Floor
          New York, NY 10286
          Facsimile No:  (212) 815-5915
          Attention:  Walter Gitlin

                                       -15-



          (c)  if given to any Holder, at the address set forth in the 
     Securities Register.

     All notices hereunder shall be deemed to have been given when received 
in person, telecopied with receipt confirmed, or mailed by first class mail, 
postage prepaid except that if a notice or other document is refused delivery 
or cannot be delivered because of a changed address of which no notice was 
given, such notice or other document shall be deemed to have been delivered 
on the date of such refusal or inability to deliver.

     SECTION 9.04.  Benefit.  This Preferred Securities Guarantee is solely 
for the benefit of the Holders and is not separately transferable from the 
Preferred Securities. 

     SECTION 9.05.  Interpretation.  In this Preferred Securities Guarantee, 
unless the context otherwise requires:

          (a)  all references to "the Preferred Securities Guarantee" or "this
     Preferred Securities Guarantee" are to this Preferred Securities Guarantee
     as modified, supplemented or amended from time to time;

          (b)  all references in this Preferred Securities Guarantee to Articles
     and Sections are to Articles and Sections of this Preferred Securities
     Guarantee unless otherwise specified;

          (c)  a term defined in the Trust Indenture Act has the same meaning
     when used in this Preferred Securities Guarantee unless otherwise defined
     in this Preferred Securities Guarantee or unless the context otherwise
     requires; 

          (d)  a reference to the singular includes the plural and vice versa;
     and

          (e)  the masculine, feminine or neuter genders used herein shall
     include the masculine, feminine and neuter genders.

     SECTION 9.06.  Governing Law.  THIS PREFERRED SECURITIES GUARANTEE SHALL 
BE GOVERNED BY AND CONSTRUED AND INTERPRETED IN ACCORDANCE WITH THE LAWS OF 
THE STATE OF NEW YORK AS APPLIED TO CONTRACTS MADE AND PERFORMED WITHIN THE 
STATE OF NEW YORK WITHOUT REGARD TO THE CONFLICT OF LAW PRINCIPLES THEREOF.

     This instrument may be executed in any number of counterparts, each of 
which so executed shall be deemed to be an original, but all such 
counterparts shall together constitute but one and the same instrument.

                                       -16-



     THIS PREFERRED SECURITIES GUARANTEE is executed as of the day and year 
first above written.

                                       PUBLIC SERVICE COMPANY OF COLORADO,
                                        as Guarantor 

                                       By:
                                          -------------------------------------
                                          Name:
                                          Title:

                                       THE BANK OF NEW YORK,
                                        as Preferred Guarantee Trustee

                                       By:
                                          -------------------------------------
                                          Name:
                                          Title:


                                       -17-