<PAGE>

                                                               EXHIBIT 4(a)(3)

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



                             SUPPLEMENTAL INDENTURE


                          DATED AS OF NOVEMBER 1, 1996



                          ____________________________



                       PUBLIC SERVICE COMPANY OF COLORADO



                                       TO


                            FIRST TRUST OF NEW YORK,
                              NATIONAL ASSOCIATION,

                                                                      AS TRUSTEE


                          ____________________________


                   Creating an Issue of First Mortgage Bonds,
                               Collateral Series D



                          ____________________________


    (Supplemental to Indenture dated as of December 1, 1939, as amended)




------------------------------------------------------------------------------ 
------------------------------------------------------------------------------ 
<PAGE>


     SUPPLEMENTAL INDENTURE, dated as of November 1, 1996, 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 
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 a new series of First Mortgage 
Bonds to be designated as First Mortgage Bonds, Collateral Series D (the 
"Collateral Series D Bonds"), to be issued and delivered from time to time to 
the trustee under the 1993 Mortgage (as hereinafter defined) as the basis for 
the authentication and delivery under the 1993 Mortgage of a series of 
securities constituting medium-term notes, 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 D 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 D Bonds and of specifying the form, provisions and 
particulars thereof, as in the Indenture provided or permitted and of giving 
to the Collateral Series D Bonds the protection and security of the 
Indenture; and

     WHEREAS, the Company has acquired the additional property hereinafter 
described, and the Company desires that such additional property so acquired 
be specifically subjected to the lien 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 D 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 
Supplemental Indenture, valid, binding and legal instruments for the security 
of the bonds of all series, including the Collateral Series D 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;

<PAGE>

     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 D Bonds 
and to specify the form, terms and provisions thereof, and to make definite 
and certain the lien of the Indenture upon the premises hereinafter described 
and to subject said premises directly to the lien of the Indenture, 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 D 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, and by these presents does grant, bargain, sell, warrant, 
alien, remise, release, convey, assign, transfer, mortgage, pledge, set over 
and confirm unto First Trust of New York, National Association, as Trustee, 
and its successor or successors in the trust and its and their assigns 
forever, the property described in Schedule B hereto (which is described in 
such manner as to fall within and under the headings or parts or 
classifications set forth in the Granting Clauses of the Principal Indenture);

     TO HAVE AND TO HOLD the same and all and singular the properties, 
rights, privileges and franchises described in the Principal Indenture and in 
the several Supplemental Indentures hereinabove referred to and in this 
Supplemental Indenture 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 D 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.


                                     -2- 
<PAGE>

                                ARTICLE ONE

         CREATION AND DESCRIPTION OF THE COLLATERAL SERIES D BONDS

     SECTION 1. A new series of bonds to be issued from time to time under and 
secured by the Indenture is hereby created, the bonds of such new series to be
designated First Mortgage Bonds, Collateral Series D.  The Collateral Series 
D Bonds shall be limited to an aggregate principal amount of Two Hundred 
Fifty Million dollars ($250,000,000), excluding any Collateral Series D Bonds 
which may be authenticated and exchanged for or in lieu of or in substitution 
for or on transfer of other Collateral Series D Bonds pursuant to any 
provisions of the Indenture.  The Collateral Series D Bonds shall not bear 
interest and each Collateral Series D Bond shall (a) be issued in such 
principal amount, (b) mature on such date not less than nine months nor more 
than thirty years from its Original Issue Date (as hereinafter defined), and 
(c) have such other terms and conditions as shall not be inconsistent with 
the provisions of the Indenture, all as shall be specified by the Company in 
a certificate, executed by the President, any Vice President, the Treasurer 
or any Assistant Treasurer of the Company, delivered to the Trustee relating 
to such Collateral Series D Bond and referring to this Supplemental Indenture 
(each such certificate being deemed to constitute a part of this Supplemental 
Indenture and being hereinafter sometimes called an "Issuance Certificate"), 
such specification by such an officer of the Company in an Issuance 
Certificate having been heretofore authorized in a resolution of the Board of 
Directors of the Company.

     The principal of each Collateral Series D Bond 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 D Bonds shall be issued and delivered from time to 
time by the Company to First Trust of New York, National Association, as 
successor trustee under the Indenture, dated as of October 1, 1993, as 
supplemented (the "1993 Mortgage"), of the Company to such trustee (the "1993 
Mortgage Trustee"), as the basis for the authentication and delivery under 
the 1993 Mortgage of a series of securities.  As provided in the 1993 
Mortgage, the Collateral Series D 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 
any 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 D Bonds (other than by the application of the 
proceeds of a payment in respect of such Collateral Series D 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 D 
Bonds which is then due.

     The Trustee may conclusively presume that the obligation of the Company 
to pay the principal of any Collateral Series D Bonds as the same shall 
become due and payable shall 

                                     -3- 
<PAGE>

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 D 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 D Bond shall be dated as of the date of its 
authentication.

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

     The Collateral Series D 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 the Collateral Series D Bonds shall not be 
transferrable except to a successor trustee under the 1993 Mortgage.  No 
service charge shall be made for any exchange or transfer of any Collateral 
Series D Bond.

     If and to the extent necessary to eliminate any apparent inconsistency 
between any provision of this Supplemental Indenture and any provision of the 
Indenture all Collateral Series D Bonds having the same Original Issue Date, 
Stated Maturity, interest rate, and other terms and conditions shall be 
deemed to be a separate series of bonds, and such Original Issue Date, Stated 
Maturity, interest rate, if any, and other terms and conditions shall be 
deemed to be a part of the designation of such series.

     As used herein, the term "Original Issue Date" shall mean, with respect 
to any Collateral Series D Bond, the date of authentication and delivery 
hereunder of such Collateral Series D Bond, or, in the case of any particular 
Collateral Series D Bond which has been authenticated and delivered upon the 
registration of transfer or exchange of, or in substitution for, another 
Collateral Series D Bond, the date of the original authentication and 
delivery hereunder of the first Collateral Series D Bond authenticated and 
delivered hereunder representing all or a portion of the same obligation as 
that evidenced by such particular Collateral Series D Bond; the term "Stated 
Maturity" shall mean, with respect to any Collateral Series D Bond, the date 
on which the principal of such Collateral Series D Bond is stated to be due 
and payable (without regard to any provision for acceleration, redemption or 
similar provisions); and the term "Maturity" shall mean, with respect to any 
Collateral Series D Bond, the date on which the principal of such Collateral 
Series D Bond becomes due and payable, whether at Stated Maturity, by 
declaration of acceleration, upon call for redemption or otherwise.

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

       SECTION 3.  The Collateral Series D 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), from time to time, in accordance 
with the written order or orders of the Company.

                                     -4- 
<PAGE>
                                ARTICLE TWO 

                 REDEMPTION OF THE COLLATERAL SERIES D BONDS

     SECTION 1.  No Collateral Series D Bond shall be subject to any sinking 
fund or other mandatory redemption (whether at the option of the holder 
thereof or otherwise) unless otherwise specified in the Issuance Certificate 
relating to such Collateral Series D Bond.  Each Collateral Series D Bond 
shall be redeemable at the option of the Company in whole at any time, or in 
part from time to time, prior to Stated 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 D Bonds, except 
that (a) no publication of notice of redemption of the Collateral Series D 
Bonds shall be required and (b) if less than all the Collateral Series D 
Bonds are to be redeemed, the Collateral Series D Bonds to be redeemed shall 
be selected from the maturities, and 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 Two.

     SECTION 3.  The holder of each and every Collateral Series D Bond issued 
hereunder hereby agrees to accept payment thereof prior to Stated Maturity on 
the terms and conditions provided for in this Article Two.
                                      
                               ARTICLE THREE

                     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 D 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 D Bonds.

                                     -5- 
<PAGE>

                                ARTICLE FOUR

                                 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 FIVE

                        MISCELLANEOUS PROVISIONS

     SECTION 1.  Subject to the variations contained in Article Two 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.

     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 and the Collateral Series D Bonds, 
have the meaning assigned to such term in Section 303 as in force on the date 
of the execution of this Supplemental Indenture.

                                     -6- 
<PAGE>

     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.




     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 or any 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 First Trust of New York, 
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 Vice Presidents and attested by one of its Assistant 
Secretaries, for and in its behalf, all as of the day and year first above 
written.

                                       PUBLIC SERVICE COMPANY OF COLORADO



                                       By:  /s/  R. C. KELLY                   
                                          ------------------------------------ 
                                          R. C. Kelly
                                          Senior Vice President, Treasurer, 
                                          and Chief Financial Officer

ATTEST: /s/  W. WAYNE BROWN         
       ---------------------------- 
       W. Wayne Brown               
       Secretary                    


                                       FIRST TRUST OF NEW YORK, 
                                       NATIONAL ASSOCIATION,
                                          AS TRUSTEE


                                       By:  /s/  CATHERINE F. DONOHUE          
                                          ------------------------------------ 
                                          Catherine F. Donohue
                                          Vice President


ATTEST: /s/  ALFIA MONASTRA        
       --------------------------- 
       Alfia Monastra
       Assistant Secretary



                                     -7- 
<PAGE>

STATE OF COLORADO          )
                           )  ss.:
CITY AND COUNTY OF DENVER  )


      On this 8th day of November, 1996, before me, Jo Lynn R. Rife, a duly 
authorized Notary Public in and for said City and County in the State 
aforesaid, personally appeared R. C. Kelly and W. Wayne Brown, to me known to 
be a Senior Vice President and the 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 R. C. Kelly and W. Wayne Brown, 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/  JO LYNN R. RIFE                    
                                       --------------------------------------- 
                                       Jo Lynn R. Rife                         
                                       Notary Public, State of Colorado        
                                       Commission Expires April 27, 1998       




                                     -8- 
<PAGE>

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


      On this 8th day of November, 1996, before me, Joanne E. Ilse, a duly 
authorized Notary Public in and for said City and County in the State 
aforesaid, personally appeared Catherine F. Donohue and Alfia Monastra, to me 
known to be a Vice President and an Assistant Secretary, respectively, of 
FIRST TRUST OF NEW YORK, National Association, a national banking 
association, one of the corporations that executed the within and foregoing 
instrument; and the said Catherine F. Donohue and Alfia Monastra, 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/  JOANNE E. ILSE                    
                                       -------------------------------------- 
                                       Joanne E. Ilse                         
                                       Notary Public, State of New York       
                                       Commission Expires October 4, 1997     




                                     -9- 
<PAGE>
                                                                   EXHIBIT A 

                        FORM OF COLLATERAL SERIES D 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 FIRST TRUST OF NEW YORK, NATIONAL ASSOCIATION, AS
SUCCESSOR TRUSTEE THEREUNDER.


                       PUBLIC SERVICE COMPANY OF COLORADO

                             FIRST MORTGAGE BOND,

                             COLLATERAL SERIES D 



REGISTERED                                                           REGISTERED 


NO..................                                                 $......... 

                       ORIGINAL ISSUE DATE:
                       STATED MATURITY:
                       OTHER/ADDITIONAL PROVISIONS:
                       ADDENDUM ATTACHED
                                  [  ] YES 
                                  [  ] 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 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 the Stated Maturity specified above (unless this bond shall then 
be deemed to have been paid in accordance with the provisions of the 
Indenture referred to below) 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 

                                    A-1 
<PAGE>

the issuance and delivery to the 1993 Mortgage Trustee of this bond (the 
"1993 Mortgage Securities") (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.

     If an Addendum is attached hereto or "Other/Additional Provisions" apply 
to this bond, this bond shall be subject to the terms set forth in such 
Addendum or such "Other/Additional Provisions".

     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 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 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 November 1, 1996 (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 D, of the 
Company. 

     Unless otherwise specified in an Addendum attached hereto, this bond 
shall not be subject to any sinking fund or other mandatory redemption 
(whether at the option of the holder hereof or otherwise).  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 the Stated Maturity specified above, at a 
redemption price equal to 100% of the principal amount thereof to be redeemed.

                                    A-2 
<PAGE>

     The principal of this bond may be declared or may become due before the 
Stated Maturity specified above, 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 and having 
the same Original Issue Date, Stated Maturity and other terms and 
conditions, 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 amount, and having the same 
Original Issue Date, Stated Maturity, and other terms and conditions, 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 
First Trust of New York, National Association, or its successor, as Trustee 
under the Indenture. 


                                    A-3 
<PAGE>

     IN WITNESS WHEREOF, Public Service Company of Colorado has caused this 
bond to be signed in its name by the facsimile signature of a Senior Vice 
President and its corporate seal to be imprinted hereon and attested by the 
facsimile signature of its Secretary.

Dated:                                 PUBLIC SERVICE COMPANY OF COLORADO     


                                       By:                                    
                                          ----------------------------------- 
                                                Senior Vice President         

ATTEST:
       ---------------------------- 
         Secretary



                         CERTIFICATE OF AUTHENTICATION


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

Dated:                                 FIRST TRUST OF NEW YORK,
                                       NATIONAL ASSOCIATION,
                                          AS TRUSTEE


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


                                    A-4 
<PAGE>

                                                                     SCHEDULE A


                          SUPPLEMENTAL INDENTURES
<TABLE>

   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                                --               -- 
</TABLE>

                                    I-1 
<PAGE>
<TABLE>

   DATE OF                                                                  PRINCIPAL  
 SUPPLEMENTAL                                              PRINCIPAL         AMOUNT    
  INDENTURE               SERIES OF BONDS                AMOUNT ISSUED     OUTSTANDING 
------------              ---------------                -------------     ----------- 
<S>                       <C>                            <C>               <C>         
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       35,000,000 
July 1, 1968*          6-3/4% Series due 1998              25,000,000       25,000,000 
April 25, 1969                 None                                --               -- 
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       22,500,000 
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 
</TABLE>

                                    I-2 
<PAGE>
<TABLE>

   DATE OF                                                                  PRINCIPAL  
 SUPPLEMENTAL                                              PRINCIPAL         AMOUNT    
  INDENTURE               SERIES OF BONDS                AMOUNT ISSUED     OUTSTANDING 
------------              ---------------                -------------     ----------- 
<S>                       <C>                            <C>               <C>         
November 1, 1986*    Pollution Control Series F            27,250,000       27,250,000 
May 1, 1987*           8.95% Series due 1992               75,000,000             None 
July 1, 1990*         9-7/8% Series due 2020               75,000,000       75,000,000 
December 1, 1990*    Secured Medium-Term Notes,           191,500,000**    108,500,000 
                             Series A                 
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     150,000,000 
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           102,667,000     102,667,000 
                    Collateral Series B due 2024           110,000,000     110,000,000 
September 2, 1994        (appointment of                          None            None 
                        successor trustee)              
May 1, 1996*        Collateral Series C due 2006           125,000,000     125,000,000 
</TABLE>

-------------------
*  Contains amendatory provisions
** $200,000,000 authorized



                                    I-3 
<PAGE>


                                                                   SCHEDULE B 

                           PROPERTY DESCRIPTION


                                PART FIRST 

                                 (Plants)  

     The following electric generating plants, gas generating plants, gas 
holders, steam plant, ice plant, pressure pipe lines, gravity pipe lines, 
reservoir sites, power sites, gas regulating stations, substations and other 
properties of the Company, including all dams, power houses, transmission 
lines, buildings, forebays, reservoirs, races, raceways, pipes, head works, 
structures and works, and the lands of the Company on which the same are 
situated, and all the Company's lands, easements, rights, rights-of-way, 
water rights, rights to the use of water, including all of the Company's 
right, title and interest in and to any and all decrees therefor, flowage 
rights, flooding rights, permits, franchises, consents, privileges, licenses, 
poles, towers, wires, switch racks, insulators, pipes, machinery, engines, 
boilers, gas benches, condensers and scrubbers, exhausters, blowers and 
pumps, motors, gas boosters, air condensers, water pumps, governors, 
purifiers, tar separators, washers, automobiles, trucks, office furniture and 
fixtures, regulators, meters, tools, appliances, equipment, appurtenances and 
supplies forming a part of or appertaining to said plants, holders, sites, 
stations or other properties, or any of them, or used or enjoyed, or capable 
of being used or enjoyed in conjunction or connection therewith, all situated 
in the State of Colorado and the counties thereof, more particularly 
described as follows:
                                      
                               ADAMS COUNTY 

1.  SKYLAKE RANCH METER STATION

A TRACT OF LAND BEING A PORTION OF THE SOUTHWEST ONE-QUARTER OF SECTION 5, 
TOWNSHIP 2 SOUTH, RANGE 67 WEST OF THE SIXTH PRINCIPAL MERIDIAN, COUNTY OF 
ADAMS, STATE OF COLORADO, BEING MORE PARTICULARLY DESCRIBED AS FOLLOWS:

BASIS OF BEARINGS:   THE NORTH LINE OF THE SOUTHWEST ONE-QUARTER OF SAID 
                     SECTION 5 BEING CONSIDERED TO BEAR N89 DEGREES 46'24"E.

COMMENCING AT THE WEST ONE-QUARTER CORNER OF SAID SECTION 5; THENCE 65 DEGREES
15'14"E A DISTANCE OF 2076.09 FEET TO A POINT ON THE SOUTHERLY LINE OF A 50.00-
FOOT WIDE COLORADO-WYOMING GAS COMPANY EASEMENT AS DESCRIBED IN BOOK 430 AT PAGE
446 IN THE ADAMS COUNTY RECORDS; THENCE S57 DEGREES 43'31"E AND ALONG THE
SOUTHERLY LINE OF SAID 50.00-FOOT COLORADO-WYOMING GAS COMPANY 

                                    II-1 
<PAGE>

EASEMENT A DISTANCE OF 125.00 FEET TO A POINT ON THE NORTHWESTERLY LINE OF A 
75.00-FOOT WIDE PUBLIC SERVICE COMPANY UTILITY EASEMENT AS DESCRIBED IN BOOK 
999 AT PAGE 261 IN THE ADAMS COUNTY RECORDS; THENCE S47 DEGREES 15'58"W AND 
ALONG THE NORTHWESTERLY LINE OF SAID 75.00-FOOT WIDE PUBLIC SERVICE COMPANY 
EASEMENT A DISTANCE OF 75.00 FEET; THENCE N57 DEGREES 43'31"W A DISTANCE OF 
125.00 FEET; THENCE N47 DEGREES 15'58"E A DISTANCE OF 75.00 FEET TO THE POINT 
OF BEGINNING, CONTAINING 9,055 SQUARE FEET OR 0.208 ACRES.




                                    II-2