Exhibit 4.2

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                             PUBLIC SERVICE COMPANY
                                   OF COLORADO

                                       TO

                              THE BANK OF NEW YORK,

                                                       AS TRUSTEE



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                          FIRST SUPPLEMENTAL INDENTURE

                            Dated as of July 15, 1999

                           Supplementing the Indenture
                            dated as of July 1, 1999


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                     Establishing the Securities of Series A
                          Senior Notes 6 7/8% due 2009



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     THIS FIRST SUPPLEMENTAL INDENTURE, dated as of July 15, 1999, is between
PUBLIC SERVICE COMPANY OF COLORADO, a Colorado corporation (hereinafter called
the "Issuer" or the "Company"), having its principal office at 1225 17th Street,
Denver, Colorado 80202, and THE BANK OF NEW YORK, as Trustee (hereinafter called
the "Trustee"), having its principal corporate trust office at 101 Barclay
Street, Floor 21 West, New York, New York 10286.


                             RECITALS OF THE ISSUER

     The Issuer has heretofore executed and delivered an Indenture, dated as of
July 1, 1999 (the "Original Indenture", the Original Indenture, as supplemented
by this supplemental indenture being hereinafter referred to as the
"Indenture"), relating to the issuance at any time or from time to time of its
Securities on terms to be specified at the time of issuance. As of the date
hereof, no Securities have been issued under the Indenture. Terms used and not
otherwise defined herein shall (unless the context otherwise clearly requires)
have the respective meanings given to them in the Original Indenture.

     The Original Indenture provides in Article Three thereof that, prior to the
issuance of Securities of any series, the form of such Securities and the terms
applicable to such series shall be established in, or pursuant to, the authority
granted in a resolution of the Board of Directors or established in one or more
indentures supplemental thereto.

     The Issuer desires by this supplemental indenture, among other things, to
establish the form of the Securities of a series, to be titled Series A Senior
Notes 6 7/8% due 2009 of the Issuer, and to establish the terms applicable to
such series, pursuant to Sections 201, 301 and 901 of the Original Indenture.
The Issuer has duly authorized the execution and delivery of this supplemental
indenture.

     Article Nine of the Original Indenture provides that the Issuer, when
authorized by a resolution of its Board of Directors, and the Trustee may from
time to time and at any time amend the Indenture without the consent of
Securityholders for certain purposes enumerated in Section 901 thereof,
including the purposes set forth in subsection (7) of said Section 901.

     The execution and delivery of this supplemental indenture by the parties
hereto are in all respects authorized by the provisions of the Indenture.

     All things necessary have been done to make this supplemental indenture a
valid agreement of the Issuer, in accordance with its terms.




     NOW, THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH:

     For and in consideration of the premises, it is mutually covenanted and
agreed, as follows:


                                   ARTICLE ONE

             ESTABLISHMENT OF SERIES A SENIOR NOTES 6 7/8% DUE 2009

     Section 1.01. The title of the series of the Securities established by this
supplemental indenture shall be Series A Senior Notes 6 7/8 % due 2009 of the
Issuer (hereinafter called the "Series A Notes").

     Section 1.02. The Series A Notes shall be limited to $200,000,000 in
aggregate principal amount.

     Section 1.03. The Series A Notes may be issued in whole or in part as one
or more Global Securities and The Depository Trust Company, or a nominee
thereof, shall be the Depository for such Global Security or Global Securities.
The Depository for such Global Security or Global Securities representing Series
A Notes may surrender one or more Global Securities representing Series A Notes
in exchange in whole or in part for individual Series A Notes on such terms as
are acceptable to the Issuer and such Depository and otherwise subject to the
terms of the Indenture.

     Section 1.04. The principal of the Series A Notes shall be payable on July
15, 2009.

     Section 1.05. The Series A Notes shall bear interest at the rate of 6 7/8%
per annum and shall accrue from July 16, 1999. The Interest Payment Dates shall
be January 15 and July 15 in each year, commencing January 15, 2000. The Regular
Record Dates in respect of such Interest Payment Dates shall be January 1 and
July 1 in each year, respectively.

     Section 1.06. The Corporate Trust Office of The Bank of New York shall be
the place at which the principal of the Series A Notes shall be payable. Any
interest thereon shall be paid as specified in Section 307 of the Original
Indenture.

     Section 1.07. The Series A Notes are subject to redemption upon not less
than 30 days' notice by first class mail, in whole at any time or in part from
time to time at the option of the Company at a redemption price equal to the
greater of (i) 100% of the principal amount hereof to be redeemed or (ii) the
sum of the present values of the remaining scheduled payments of principal and
interest thereon discounted to the redemption date on a semiannual basis
(assuming a 360 day year consisting of


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twelve 30-day months) at the Treasury Yield plus 15 basis points, plus in each
case accrued and unpaid interest to the redemption date.

     "Treasury Yield" means, with respect to any redemption date, the rate per
annum equal to the semiannual equivalent yield to maturity of the Comparable
Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as
a percentage of its principal amount) equal to the Comparable Treasury Price for
such redemption date.

     "Comparable Treasury Issue" means the United States Treasury security
selected by an Independent Investment Banker as having a maturity comparable to
the remaining term hereof that would be utilized, at the time of selection and
in accordance with customary financial practice, in pricing new issues of
corporate debt securities of comparable maturity to the remaining term hereof.
"Independent Investment Banker" means Merrill Lynch, Pierce, Fenner & Smith
Incorporated or, if such firm is unwilling or unable to select the Comparable
Treasury Issue, one of the remaining Reference Treasury Dealers appointed by the
Trustee after consultation with the Company.

     "Comparable Treasury Price" means, with respect to any redemption date, (i)
the average of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) on the third
business day preceding such Redemption date, as set forth in the daily
statistical release (or any successor release) published by the Federal Reserve
Bank of New York and designated "Composite 3:30 p.m. Quotations for U.S.
Government Securities" or (ii) if such release (or any successor release) is not
published or does not contain such prices on such business day, (A) the average
of the Reference Treasury Dealer Quotations for such redemption date, after
excluding the highest and lowest such Reference Treasury Dealer Quotations for
such redemption date, or (B) if the Trustee obtains fewer than four such
Reference Treasury Dealer Quotations, the average of all such Quotations.
"Reference Treasury Dealer Quotations" means, with respect to each Reference
Treasury Dealer and any Redemption date, the average, as determined by the
Company, of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) quoted in
writing to the Company by such Reference Treasury Dealer at 5:00 p.m. on the
third business day preceding such redemption date.

     "Reference Treasury Dealer" means (i) any primary U.S. Government
securities dealer in New York City (a "Primary Treasury Dealer") designated by
the Company.

     In the event of redemption of the Series A Notes in part only, a new Series
A Note or Notes of the same series for


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the unredeemed portion thereof will be issued in the name of the Holder thereof
upon the cancellation hereof.

     Section 1.08. Notice of redemption will be mailed at least 30 days before
the redemption date to the Holder thereof at his address appearing on the
Security Register. A notice of redemption shall provide that it is subject to
the occurrence of any event before the date fixed for such redemption as
described in such notice ("Conditional Redemption") and such notice of
Conditional Redemption shall be of no effect unless all such conditions to the
redemption have occurred before such date or have been waived by the Company.

     Section 1.09. The Series A Notes shall be issued in denominations of $1000
and any integral multiple thereof.

     Section 1.10. Sections 1301 and 1302 of the Indenture shall be applicable
to the Series A Notes.

     Section 1.11. The Issuer hereby appoints, or confirms the appointment of,
The Bank of New York as the initial Trustee, Securities Registrar and Paying
Agent, subject to the provisions of the Indenture with respect to resignation,
removal and succession, and subject, further, to the right of the Issuer to
appoint additional agents (including Paying Agents).

     Section 1.12. The Series A Notes shall be substantially in the form set
forth in EXHIBIT A hereto, and shall have such further terms as are reflected in
such form, subject to changes in the form thereof made by the Issuer and
acceptable to the Trustee.


                                   ARTICLE TWO

                                  MISCELLANEOUS

     Section 2.01. The recitals contained herein shall be taken as the
statements of the Issuer, and the Trustee assumes no responsibility for the
correctness of the same. The Trustee makes no representation as to the validity
of this supplemental indenture. The Indenture, as supplemented by this
supplemental indenture, is in all respects hereby adopted, ratified and
confirmed.

     Section 2.02. This supplemental indenture may be executed in any number of
counterparts, and on separate counterparts, each of which shall be an original;
but such counterparts shall together constitute but one and the same instrument.


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     Section 2.03. If any provision of this supplemental indenture limits,
qualifies or conflicts with the duties imposed by any of Sections 310 to 317,
inclusive, of the Trust Indenture Act of 1939, as amended by the Trust Indenture
Reform Act of 1990, through operation of Section 318(c), such imposed duties
shall control.

     Section 2.04. The Article headings herein are for convenience only and
shall not affect the interpretation hereof.


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     IN WITNESS WHEREOF, the parties hereto have caused this First Supplemental
Indenture to be duly executed as of the 15th day of July, 1999.


                                       PUBLIC SERVICE COMPANY OF COLORADO



                                       By:   /s/ Richard C. Kelly
                                           --------------------------
                                             Richard C. Kelly
                                             Executive Vice President


                                       THE BANK OF NEW YORK



                                       By:   /s/ Walter N. Gitlin
                                           --------------------------
                                             Authorized Signatory


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                                    EXHIBIT A

                  Form of Series A Senior Note 6 7/8% due 2009

     THIS SECURITY IS A GLOBAL SECURITY REGISTERED IN THE NAME OF THE DEPOSITORY
(REFERRED TO HEREIN) OR A NOMINEE THEREOF AND UNLESS AND UNTIL IT IS EXCHANGED
IN WHOLE OR IN PART FOR THE INDIVIDUAL SECURITIES REPRESENTED HEREBY, THIS
GLOBAL SECURITY MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITORY TO A
NOMINEE OF THE DEPOSITORY OR BY A NOMINEE OF THE DEPOSITORY TO THE DEPOSITORY OR
ANOTHER NOMINEE OF THE DEPOSITORY OR BY THE DEPOSITORY OR ANY SUCH NOMINEE TO A
SUCCESSOR DEPOSITORY OR A NOMINEE OF SUCH SUCCESSOR DEPOSITORY.

     UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (55 WATER STREET, NEW YORK, NEW
YORK), TO THE TRUSTEE FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY
CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH OTHER NAME
AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY
AND ANY PAYMENT IS MADE TO CEDE & CO., ANY TRANSFER, PLEDGE OR OTHER USE HEREOF
FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE
REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.


                     PUBLIC SERVICE COMPANY OF COLORADO
                    Series A Senior Note 6 7/8 % due 2009



                 Interest Rate:    6 7/8%
        Interest Payment Dates:    January 15 and July 15
          Regular Record Dates:    January 1 and July 1
Original Interest Accrual Date:    January 16,1999
               Stated Maturity:    July 15,2009


CUSIP No. ___________              Principal Amount
                                   $200,000,000


     PUBLIC SERVICE COMPANY OF COLORADO, a corporation duly organized and
existing under the laws of the State of Colorado (herein called the "Company",
which term includes any successor


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corporation under the Indenture referred to below) promises to pay to
_____________________________________ or registered assigns the principal sum of
Two Hundred Million Dollars on July 15, 2009, the Stated Maturity specified
above.


1.   Interest.

          The Company promises to pay interest on the principal amount hereof at
          the Interest Rate per annum shown above from the Original Interest
          Accrual Date specified above, or from the most recent Interest Payment
          Date to which interest has been paid, semiannually in arrears, on the
          Interest Payment Dates specified above, in each year, commencing with
          the Interest Payment Date next succeeding the Original Interest
          Accrual Date specified above, until the principal hereof is paid or
          duly provided for. Interest will be computed on the basis of a 360-day
          year of twelve 30-day months.

2.   Method of Payment.

          The Company will pay interest so payable to the person who is the
          registered holder hereof at the close of business on the Regular
          Record Date for the next Interest Payment Date, except as otherwise
          provided in the Indenture and except that interest payable at Maturity
          will be paid to the person to whom principal is paid at Maturity.
          Payment of principal shall be made upon presentation hereof at the
          office of this Paying Agent. The Company will pay principal and
          interest in money of the United States that at the time of payment is
          legal tender for payment of public and private debts. The Company may
          pay principal and interest by check payable in such money. It may mail
          an interest check to the holder's registered address.

3.   Agents.

          Initially, The Bank of New York, 101 Barclay Street, Floor 21 West,
          New York, New York 10286 Attention: Corporate Trust Administration,
          will act as Paying Agent and Securities Registrar. The Company may
          change the Paying Agent to provide for more than one such agent. The
          Company may appoint one or more Security Registrars. The Company or
          any Affiliate may act in any such capacity. The Trustee may appoint
          one or more Authenticating Agents to authenticate the Securities.

4.   Indenture.

          The securities of this series (the "Securities") have been issued
          under an Indenture dated as of July 1, 1999


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          (the "Indenture") between the Company and The Bank of New York (the
          "Trustee," which term includes any successor trustee under the
          Indenture). The terms of the Securities include those stated in the
          Indenture and in the Supplemental Indenture creating the Securities
          and those made part of the Indenture by the Trust Indenture Act of
          1939 (15 U.S. Code Sections 77aaa-77bbbb). Securityholders are
          referred to the Indenture, the Supplemental Indenture and the Trust
          Indenture Act of 1939, as amended, for a statement of such terms.

5.   Redemption.

          This Security is subject to redemption upon not less than 30 days'
          notice by first class mail, in whole at any time or in part from time
          to time at the option of the Company at a redemption price equal to
          the greater of (i) 100% of the principal amount hereof to be redeemed
          or (ii) the sum of the present values of the remaining scheduled
          payments of principal and interest thereon discounted to the
          redemption date on a semiannual basis (assuming a 360 day year
          consisting of twelve 30-day months) at the Treasury Yield plus 15
          basis points, plus in each case accrued and unpaid interest to the
          redemption date.

               "Treasury Yield" means, with respect to any redemption date, the
          rate per annum equal to the semiannual equivalent yield to maturity of
          the Comparable Treasury Issue, assuming a price for the Comparable
          Treasury Issue (expressed as a percentage of its principal amount)
          equal to the Comparable Treasury Price for such redemption date.

               "Comparable Treasury Issue" means the United States Treasury
          security selected by an Independent Investment Banker as having a
          maturity comparable to the remaining term hereof that would be
          utilized, at the time of selection and in accordance with customary
          financial practice, in pricing new issues of corporate debt securities
          of comparable maturity to the remaining term hereof. "Independent
          Investment Banker" means Merrill Lynch, Pierce, Fenner & Smith
          Incorporated or, if such firm is unwilling or unable to select the
          Comparable Treasury Issue, one of the remaining Reference Treasury
          Dealers appointed by the Trustee after consultation with the Company.

               "Comparable Treasury Price" means, with respect to any redemption
          date, (i) the average of the bid and asked prices for the Comparable
          Treasury Issue (expressed in each case as a percentage of its
          principal amount) on the third business day preceding such


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          Redemption date, as set forth in the daily statistical release (or any
          successor release) published by the Federal Reserve Bank of New York
          and designated "Composite 3:30 p.m. Quotations for U.S. Government
          Securities" or (ii) if such release (or any successor release) is not
          published or does not contain such prices on such business day, (A)
          the average of the Reference Treasury Dealer Quotations for such
          redemption date, after excluding the highest and lowest such Reference
          Treasury Dealer Quotations for such redemption date, or (B) if the
          Trustee obtains fewer than four such Reference Treasury Dealer
          Quotations, the average of all such Quotations. "Reference Treasury
          Dealer Quotations" means, with respect to each Reference Treasury
          Dealer and any Redemption date, the average, as determined by the
          Company, of the bid and asked prices for the Comparable Treasury Issue
          (expressed in each case as a percentage of its principal amount)
          quoted in writing to the Company by such Reference Treasury Dealer at
          5:00 p.m. on the third business day preceding such redemption date.

               "Reference Treasury Dealer" means (i) any primary U.S. Government
          securities dealer in New York City (a "Primary Treasury Dealer")
          designated by the Company.

               In the event of redemption of this Security in part only, a new
          Security or Securities of this series for the unredeemed portion
          hereof will be issued in the name of the Holder hereof upon the
          cancellation hereof.

6.   Notice of Redemption.

          Notice of redemption will be mailed at least 30 days before the
          redemption date to the holder hereof at his address appearing on the
          Security Register.

          A notice of redemption shall provide that it is subject to the
          occurrence of any event before the date fixed for such redemption as
          described in such notice ("Conditional Redemption") and such notice of
          Conditional Redemption shall be of no effect unless all such
          conditions to the redemption have occurred before such date or have
          been waived by the Company.

7.   Denominations, Transfer, Exchange.

          The Securities of this series are in registered form without coupons
          in denominations of $1000 and whole multiples of $1000. The transfer
          of this Security may be registered and this Security may be exchanged
          as provided in the Indenture. The Securities Registrar may require a
          holder, among other things, to furnish


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          appropriate endorsements and transfer documents and to pay any taxes
          and fees required by law or the Indenture. The Securities Registrar
          need not exchange or register the transfer of any Security of this
          series or portion thereof selected for redemption. Also, it need not
          exchange or register the transfer of any Security for a period of 15
          days before the mailing of a notice of redemption of Securities of
          this series selected to be redeemed.

8.   Persons Deemed Owners.

          The registered holder of a Security may be treated as its owner for
          all purposes.

9.   Amendments and Waivers.

          Subject to certain exceptions, the Indenture may be amended with the
          consent of the holders of a majority in outstanding principal amount
          of the Securities. Subject to certain exceptions, a default under the
          Indenture may be waived with the consent of the holders of a majority
          in outstanding principal amount of the Securities.

          Without the consent of any Securityholder, the Indenture may be
          amended, among other things, to cure any ambiguity, omission, defect
          or inconsistency; to provide for assumption of Company obligations to
          Securityholders; or to make any change that does not materially
          adversely affect the rights of any Securityholder.

10.  Restrictive Covenants.

          The Securities are unsecured general obligations of the Company
          limited to $200,000,000 principal amount. The Indenture does not limit
          the amount of debt the Company may issue thereunder or otherwise.

11.  Successors.

          When a successor assumes all the obligations of the Company under the
          Securities and the Indenture, the Company will be released from those
          obligations.

12.  Defeasance Prior to Redemption or Maturity.

          Subject to certain conditions, the Company at any time may terminate
          some or all of its obligations hereunder and the Indenture if the
          Company deposits with the Trustee money or U.S. Government Obligations
          for the payment of principal and interest hereon to redemption or
          maturity. U.S. Government Obligations are securities backed by the
          full faith and credit of the United States


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          of America or certificates representing an ownership interest in such
          Obligations.

13.  Defaults and Remedies.

          If an Event of Default occurs and is continuing, the Trustee or the
          holders of at least 25% in principal amount of the outstanding
          Securities may declare the principal of all such Securities to be due
          and payable immediately.

          Securityholders may not enforce the Indenture or the Securities except
          as provided in the Indenture. The Trustee may require indemnity
          satisfactory to it before it enforces the Indenture or the Securities.
          Subject to certain limitations, holders of a majority in principal
          amount of the Securities may direct the Trustee in its exercise of any
          trust or power. The Trustee may withhold from Securityholders notice
          of any continuing default (except a default in payment) if it
          determines that withholding notice is in their interests. The Company
          must furnish annual compliance certificates to the Trustee.

14.  Trustee Dealings with Company.

          The Bank of New York, the Trustee under the Indenture, in its
          individual or any other capacity, may make loans to, accept deposits
          from, and perform services for the Company or its Affiliates, and may
          otherwise deal with the Company or its Affiliates, as if it were not
          Trustee.

15.  No Recourse Against Others.

          A director, officer, employee or stockholder, as such, of the Company
          shall not have any liability for any obligations of the Company under
          the Securities or the Indenture or for any claim based on, in respect
          of or by reason of such obligations or their creation. Each
          Securityholder by accepting a Security waives and releases all such
          liability. The waiver and release are part of the consideration for
          the issue of the Securities.

16.  Authentication.

          This Security shall not be valid for any purpose and shall not be
          entitled to any benefit under the Indenture until authenticated by a
          manual signature of the Trustee or any Authenticating Agent.


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17.  Abbreviations.

          Customary abbreviations may be used in the name of a Securityholder or
          an assignee, such as: TEN COM (tenants in common), TEN ENT (tenants by
          the entireties), JT TEN (joint tenants with right of survivorship and
          not as tenants in common), CUST (custodian), and U/G/M/A (Uniform
          Gifts to Minors Act).



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          The Company will furnish to any Securityholder upon written request
and without charge a copy of the Indenture, including the Supplemental
Indenture which contains the text of this Security in larger type. Requests
may be made to: Public Service Company of Colorado, 1225 17th Street, Denver,
Colorado, 80202 attention: Corporate Secretary.


    [Corporate Seal]                              PUBLIC SERVICE
                                                  COMPANY OF COLORADO



                                             By: _______________________
                                                  name:
                                                  title:

Attest:

By:__________________
   name:
   title:


Authenticated:



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


                                             THE BANK OF NEW YORK,
                                             as Trustee


Dated: July 16, 1999                         By: ____________________________
                                                  Authorized Signatory


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                                 ASSIGNMENT FORM


                To assign this Security, fill in the form below:

                  I or we assign and transfer this Security to:

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

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


               (Insert assignee's social security or tax I.D. no.)


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

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

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

     (Print or type assignee's name, address and zip code)


and irrevocably appoint __________________________________ agent to transfer
this Security on the books of the Company. The agent may substitute another to
act for him.



Date:_________________                       Your Signature:___________________



     (Sign exactly as your name appears on the other side of this Security)


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