Document:

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                                                                     EXHIBIT 4.1

                             SUPPLEMENTAL INDENTURE

         This SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as
of February 19, 2002 but effective as of the Effective Time (as defined below),
between Orion Power Holdings, Inc., a Delaware corporation (the "Company"), and
Wilmington Trust Company, as trustee (the "Trustee"), supplements the Indenture
dated as of June 6, 2001 (the "Indenture") between the Company and the Trustee
relating to the Company's 4.50% Convertible Senior Notes due 2008 (the "Notes").

                                    RECITALS

                  WHEREAS, pursuant to the terms of the Indenture, the Notes
were convertible into shares of common stock, par value $.01 per share ("Common
Stock"), of the Company prior to the Effective Time (as defined below);

                  WHEREAS, pursuant to an Agreement and Plan of Merger dated as
of September 26, 2001, among Reliant Resources, Inc., Reliant Energy Power
Generation Merger Sub, Inc. ("Merger Sub") and the Company (the "Merger
Agreement"), Merger Sub will be merged with and into the Company, with the
Company to be the surviving corporation (the "Merger"), and as a result of which
each outstanding share of Common Stock will be converted at the effective time
of the Merger (the "Effective Time") into the right to receive $26.80 in cash
(the "Merger Consideration"), as set forth in the Merger Agreement;

                  WHEREAS, Section 5.13 of the Merger Agreement and Section
10.11 of the Indenture require that the Company enter into a supplemental
indenture providing that the holder of each Note outstanding at the time of the
Merger shall have the right thereafter to convert such Note into the amount of
cash receivable upon consummation of the Merger by a holder of the number of
shares of Common Stock into which such Note might have been converted
immediately prior to the Merger; and

                  WHEREAS, Section 9.01 of the Indenture provides that the
Company and the Trustee may supplement the Indenture without the consent of any
holder of Notes to make provision with respect to the conversion rights of
holders of the Notes pursuant to Section 10.11 of the Indenture;

         NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, and to comply with Sections 10.11 and 9.01 of the Indenture and
Section 5.13 of the Merger Agreement, the Company and the Trustee agree as
follows for the benefit of each other and for the equal and ratable benefit of
the Holders of the Notes:

         Section 1. Capitalized Terms. Capitalized terms used and not otherwise
defined in this Supplemental Indenture shall have the respective meanings
assigned to such terms in the Indenture.

         Section 2. Compliance with Indenture Provisions. Concurrently with the
execution and delivery of this Supplemental Indenture, the Company has delivered
to the Trustee an Officer's

                                      -1-

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Certificate and an Opinion of Counsel as required by Sections 7.02 and 9.06 of
the Indenture. The Company shall give or cause to be given notice of the
execution of this Supplemental Indenture to the Holder of each Note as required
by the Indenture.

         Section 3. Adjustment of Conversion Privilege. The Holder of each Note
outstanding immediately prior to the Effective Time (and each subsequent Holder)
shall have the right from and after the Effective Time, during the period such
Note shall be convertible as specified in Section 10.01 of the Indenture, to
convert such Note only into the amount of cash receivable upon the Merger by a
holder of the number of shares of Common Stock into which such Note might have
been converted immediately prior to the Merger. For the avoidance of doubt, (a)
the rate at which shares of Common Stock were deliverable upon conversion of
Notes immediately prior to the Effective Time was 29.2505 shares for each $1,000
principal amount of Notes and (b) the amount of cash receivable upon the Merger
by a holder of 29.2505 shares of Common Stock is $783.91.

         Section 4. Ratification. The Indenture, as supplemented by this
Supplemental Indenture, is in all respects ratified and confirmed by the
Company, and all of the rights and powers created thereby or thereunder shall be
and remain in full force and effect.

         Section 5. Trustee Disclaimer. The Trustee accepts the amendment of the
Indenture effected by this First Supplemental Indenture and agrees to execute
the trust created by the Indenture as hereby amended, but only upon the terms
and conditions set forth in the Indenture, including Section 10.13 of the
Indenture and all other terms and provisions defining and limiting the
liabilities and responsibilities of the Trustee, which terms and provisions
shall in like manner define and limit its liabilities and responsibilities in
the performance of the trust created by the Indenture as hereby amended. Without
limiting the generality of the foregoing, the Trustee shall not be responsible
in any manner whatsoever for or with respect to any of the recitals or
statements contained herein, all of which recitals or statements are made solely
by the Company, or for or with respect to (i) the Conversion Rate or the
validity, efficacy, or sufficiency of this First Supplemental Indenture or any
of the terms or provisions hereof, (ii) the proper authorization hereof by the
Company by corporate action or otherwise, or (iii) the due execution hereof by
the Company and the Trustee makes no representation with respect to any such
matters.

         Section 6. Governing Law. The internal law of the State of New York
shall govern and be used to construe this Supplemental Indenture without giving
effect to applicable principles of conflict of law to the extent that the
application of the laws of another jurisdiction would be required thereby.

         Section 7. Successors. All agreements of the Company and the Trustee in
this Supplemental Indenture shall bind their respective successors.

         Section 8. Counterpart Originals. The parties hereto may sign any
number of copies of this Supplemental Indenture. Each signed copy shall be an
original, but all of them together represent the same agreement.

                                      -2-
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         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed as of the day and year first above written.

                                    ORION POWER HOLDINGS, INC.

                                    By:    /s/ Scott B. Helm
                                       -----------------------------------------
                                         Name:   Scott B. Helm
                                         Title:  Executive Vice President and
                                                 Chief Financial Officer

                                    WILMINGTON TRUST COMPANY,
                                    as Trustee

                                    By:   /s/ David A. Vanaskey, Jr.
                                        ----------------------------------------
                                         Name:   David A. Vanaskey, Jr.
                                         Title:  Vice President

                                      -3-<PAGE>

                                                                  Exhibit 4.1(a)

REGISTERED
No. 1

                                KRAFT FOODS INC.

                              5 1/4% NOTE DUE 2007

                                  representing

                                  $400,000,000

CUSIP No. 50075N AG 9         ISIN No. US50075NAG97     Common Code No. 14840311

THIS NOTE IS A GLOBAL SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER
REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF.
UNLESS AND UNTIL IT IS EXCHANGED IN WHOLE OR IN PART FOR NOTES IN CERTIFICATED
FORM, THIS NOTE MAY NOT BE TRANSFERRED EXCEPT AS A WHOLE BY THE DEPOSITORY TRUST
COMPANY (THE "DEPOSITARY") TO A NOMINEE OF THE DEPOSITARY OR BY THE DEPOSITARY
OR ANY SUCH NOMINEE TO A SUCCESSOR DEPOSITARY OR A NOMINEE OF SUCH SUCCESSOR
DEPOSITARY. UNLESS THIS NOTE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE
DEPOSITARY TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR
PAYMENT, AND ANY NOTE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR IN SUCH
OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY
(AND ANY PAYMENT IS MADE TO CEDE & CO. OR TO SUCH OTHER ENTITY AS IS REQUESTED
BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITARY), 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.

     KRAFT FOODS INC., a Virginia corporation (hereinafter called the "Company,"
which term includes any successor corporation under the Indenture hereinafter
referred to), for value received, hereby promises to pay to Cede & Co. or
registered assigns, the principal sum of $400,000,000 on June 1, 2007, and to
pay interest thereon from May 20, 2002 or from the most recent Interest
Payment Date to which interest has been paid or duly provided for, semiannually
on June 1 and December 1 in each year, commencing December 1, 2002, at the rate
of 5 1/4% per annum until the principal hereof is paid or made available for
payment.

     The interest so payable, and punctually paid or duly provided for, on any
Interest Payment Date will, as provided in the Indenture, be paid to the Person
in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on the Regular Record Date for such interest, which shall
be May 15 or November 15 (whether or not a Business Day), as the case may be,
next preceding such Interest Payment Date. Any such

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interest not so punctually paid or duly provided for shall forthwith cease to be
payable to the Holder on such Regular Record Date and may be paid to the Person
in whose name this Note (or one or more Predecessor Securities) is registered at
the close of business on a Special Record Date for the payment of such Defaulted
Interest to be fixed by the Trustee for the Notes, notice whereof shall be given
to Holders of Notes not less than 10 days prior to such Special Record Date, or
may be paid at any time in any other lawful manner not inconsistent with the
requirements of any securities exchange on which the Notes may be listed, and
upon such notice as may be required by such exchange, all as more fully provided
in said Indenture.

     Payment of the principal of and interest on this Note will be made at the
office or agency of the Company maintained for that purpose in the Borough of
Manhattan, The City of New York, in such coin or currency of the United States
of America as at the time of payment is legal tender for payment of public and
private debts; provided, however, that at the option of the Company payment of
               --------  -------
interest may be made by check mailed to the address of the Person entitled
thereto as such address shall appear on the Securities Register or by wire
transfer to an account maintained by the payee at a bank located in the United
States. All payments of principal and interest in respect of this Note will be
made by the Company in immediately available funds.

     Additional provisions of this Note are contained on the reverse hereof, and
such provisions shall have the same effect as though fully set forth in this
place.

     Unless the certificate of authentication hereon has been executed by or on
behalf of the Trustee for the Notes by manual signature, this Note shall not be
entitled to any benefit under the Indenture, or be valid or obligatory for any
purpose.

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     IN WITNESS WHEREOF, KRAFT FOODS INC. has caused this instrument to be duly
executed under its corporate seal.

Dated:  May 20, 2002

                                            KRAFT FOODS INC.

                                            By: /s/ James P. Dollive
                                                ---------------------------
                                                Name:  James P. Dollive
                                                Title: Senior Vice President and
                                                       Chief Financial Officer
[SEAL]
                                            Attest:

                                            By: /s/ Calvin J. Collier
                                                ---------------------------
                                                Name:  Calvin J. Collier
                                                Title: Senior Vice President,
                                                       General Counsel and
                                                       Corporate Secretary

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                          CERTIFICATE OF AUTHENTICATION

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

                                                     JPMORGAN CHASE BANK,
                                                         as Trustee

                                                         /s/ Robert S. Peschler
                                                     By: -----------------------
                                                           Authorized Officer

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                                (Reverse of Note)

                                KRAFT FOODS INC.

     This Note is one of a duly authorized issue of debentures, notes or other
evidences of indebtedness (hereinafter called the "Securities") of the Company
of the series hereinafter specified, which series is initially issued in the
aggregate principal amount of $1,000,000,000, all such Securities issued and to
be issued under an Indenture dated as of October 17, 2001 between the Company
and The Chase Manhattan Bank (now known as JPMorgan Chase Bank), as Trustee
(herein called the "Indenture"), to which Indenture and all other indentures
supplemental thereto reference is hereby made for a statement of the rights and
limitations of rights thereunder of the Holders of the Securities and of the
rights, obligations, duties and immunities of the Trustee for each series of
Securities and of the Company, and the terms upon which the Securities are and
are to be authenticated and delivered. As provided in the Indenture, the
Securities may be issued in one or more series, which different series may be
issued in various aggregate principal amounts, may mature at different times,
may bear interest, if any, at different rates, may be subject to different
redemption provisions, if any, may be subject to different sinking, purchase or
analogous funds, if any, may be subject to different covenants and Events of
Default and may otherwise vary as in the Indenture provided or permitted. This
Note is one of a series of the Securities designated therein as 5 1/4% Notes due
2007 (the "Notes").

     The Company may, without the consent of the Holders of the Notes, issue
additional notes having the same ranking and the same interest rate, maturity
and other terms as the Notes, except for the issue price and issue date. Any
additional notes having such similar terms, together with the Notes, will
constitute a single series of notes under the Indenture. No additional notes may
be issued if an Event of Default has occurred with respect to the Notes.

     Section 1010 of the Indenture shall be applicable to the Notes, except that
the term "Holder," when used in Section 1010 of the Indenture, shall mean the
beneficial owner of a Note or any person holding on behalf or for the account of
the beneficial owner of a Note.

     The Indenture contains provisions for defeasance at any time of the entire
principal of all the Securities of any series upon compliance by the Company
with certain conditions set forth therein.

     If an Event of Default (other than an Event of Default described in Section
501(4) or 501(5) of the Indenture) with respect to the Notes shall occur and be
continuing, then either the Trustee or the Holders of not less than 25% in
principal amount of the Notes of this series then Outstanding may declare the
entire principal amount of the Notes of this series due and payable in the
manner and with effect provided in the Indenture. If an Event of Default
specified in Section 501(4) or 501(5) occurs with respect to the Company, all of
the unpaid principal amount and accrued interest then outstanding shall ipso
facto become and be immediately due and payable in the manner with the effect
provided in the Indenture without any declaration or other act by the Trustee or
any Holder.

     The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the

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rights of the Holders of the Securities under the Indenture at any time by the
Company with the consent of the Holders of more than 50% in aggregate principal
amount of the Securities at the time Outstanding of each series issued under the
Indenture to be affected thereby. The Indenture also contains provisions
permitting the Holders of specified percentages in aggregate principal amount of
the Securities of that series at the time Outstanding, on behalf of the Holders
of all the Securities of such series, to waive compliance by the Company with
certain provisions of the Indenture and certain past defaults under the
Indenture and their consequences with respect to such series. Any such consent
or waiver by the Holder of this Note shall be conclusive and binding upon such
Holder and upon all future Holders of this Note and of any Note issued upon the
transfer hereof or in exchange or in lieu hereof whether or not notation of such
consent or waiver is made upon this Note.

     No reference herein to the Indenture and no provision of this Note or of
the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of and interest on this Note at
the times, place and rate, and in the coin or currency, herein and in the
Indenture prescribed.

     As provided in the Indenture and subject to certain limitations therein set
forth, this Note is transferable on the Security Register of the Company, upon
surrender of this Note for registration of transfer at the office or agency of
the Company to be maintained for that purpose in the Borough of Manhattan, The
City of New York, or at any other office or agency of the Company maintained for
that purpose, duly endorsed by, or accompanied by a written instrument of
transfer in form satisfactory to the Company and the Security Registrar duly
executed by the Holder hereof or his attorney duly authorized in writing, and
thereupon one or more new Notes, of authorized denominations and for the same
aggregate principal amount, will be issued to the designated transferee or
transferees.

     The Notes are issuable only in registered form without coupons in
denominations of $1,000 and any multiple of $1,000. As provided in the Indenture
and subject to certain limitations therein set forth, Notes are exchangeable for
a like aggregate principal amount of Notes of a like tenor and of a different
authorized denomination, as requested by the Holder surrendering the same.

     No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

     The Company, the Trustee for the Notes and any agent of the Company or such
Trustee may treat the Person in whose name this Note is registered as the owner
hereof for the purpose of receiving payment as herein provided and for all other
purposes, whether or not this Note be overdue, and neither the Company, such
Trustee nor any such agent shall be affected by notice to the contrary.

     Certain of the Company's obligations under the Indenture with respect to
Notes, may be terminated if the Company irrevocably deposits with the Trustee
money or Government Obligations sufficient to pay and discharge the entire
indebtedness on all Notes, as provided in the Indenture.

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     This Note shall for all purposes be governed by, and construed in
accordance with, the laws of the State of New York.

     Certain terms used in this Note which are defined in the Indenture have the
meanings set forth therein.

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                                 ASSIGNMENT FORM

  FOR VALUE RECEIVED, the undersigned hereby sells, assigns and transfers unto

PLEASE INSERT SOCIAL SECURITY NUMBER OR
OTHER IDENTIFYING NUMBER OF ASSIGNEE

________________________________________________________________________________
                                              (Name and address of Assignee,
                                              including zip code, must be
                                              printed or typewritten)

________________________________________________________________________________

________________________________________________________________________________
the within Note, and all rights thereunder, hereby irrevocably, constituting and
appointing

________________________________________________________________________________

_______________________________________________________________________ Attorney
to transfer the said Note on the books of Kraft Foods Inc. with full power of
substitution in the premises.

Dated: ____________________     ________________________________________________
                                NOTICE: The signature of this assignment must
                                        correspond with the name as it appears
                                        upon the face of the within Note in
                                        every particular, without alteration or
                                        enlargement or any change whatever.

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