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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

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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.

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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






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