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                                                                     EXHIBIT 4.8

                              ASSUMPTION AGREEMENT

         ASSUMPTION AGREEMENT, dated as of December [ ], 2001 (this
"Agreement"), made by Edison Mission Holdings Co., a California corporation
("Holdings"), The Bank of New York, as successor in interest to United States
Trust Company of New York, as Bondholder Trustee under the Indenture (as defined
below), The Bank of New York as successor in intereset to United States Trust
Company of New York, as Collateral Agent under the Guarantee and Collateral
Agreement (as defined below) and EME Homer City Generation L.P., a Pennsylvania
limited partnership ("EME Homer City").

                                    RECITALS

         WHEREAS, Edison Mission Holdings Co. ("Holdings") entered into the
Indenture, dated as of May 27, 1999, between Holdings and the Bondholder Trustee
(as amended from time to time, the "Indenture") pursuant to which Holdings
issued 8.137% Senior Secured Bonds due 2019 and 8.734% Senior Secured Bonds due
2026 which it subsequently exchanged for a like amount of substantially similar
bonds that had been registered under the Securities Act of 1933 (collectively,
the "Bonds").

         WHEREAS, the direct and indirect subsidiaries of Holdings, including
EME Homer City (collectively, the "Subsidiary Guarantors") entered into the
Guarantee and Collateral Agreement, dated as of March 18, 1999, among Holdings,
each Subsidiary Guarantor and the Collateral Agent (as amended from time to
time, the "Guarantee and Collateral Agreement") pursuant to which each
Subsidiary Guarantor unconditionally guaranteed the obligations of Holdings
under the Indenture and the Bonds.

         WHEREAS, in connection with a sale-leaseback transaction involving
certain facilities owned by EME Homer City, each Subsidiary Guarantor was
released from its respective obligations under the Guarantee and Collateral
Agreement.

         WHEREAS, EME Homer City desires to expressly assume all obligations of
Holdings under the Indenture and the Bonds, and Holdings desires to be released
from all obligations under the Indenture and the Bonds.

         NOW THEREFORE, for and in consideration of the mutual promises and
covenants set forth herein:

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         1. ASSUMPTION. EME Homer City hereby unconditionally and irrevocably
assumes all obligations of Holdings under the Indenture and the Bonds. Holdings
is released from its obligations under the Indenture and the Bonds.

         2. ACCEPTANCE. Holdings hereby accepts this assumption of all its
obligations under the Indenture and the Bonds.

         3. ACKNOWLEDGMENTS.

         (a)      The Bondholder Trustee acknowledges that, as a consequence of
                  the assignment and assumption contained herein, Holdings does
                  not have any liability under the Bonds and the Bondholder
                  Trustee agrees, and by its acceptance, each holder of a Bond
                  agrees, that it will not look to Holdings for payments of any
                  amounts owed in respect of the Bonds.

         (b)      The Collateral Agent acknowledges that the Subsidiary
                  Guarantors have been released from their obligations under the
                  Guarantee and Collateral Agreement pursuant to SECTION 8.14(B)
                  thereof.

         4. BINDING OBLIGATION. Each of Holdings, EME Homer City, the Bondholder
Trustee and the Collateral Agent hereby represents that its respective
obligations under this Agreement constitute its legal, valid and binding
obligations, enforceable in accordance with their respective terms.

         5. SUCCESSORS AND ASSIGNS. This Agreement shall inure to the benefit of
and be binding upon Holdings, EME Homer City, the Bondholder Trustee and the
Collateral Agent and their respective heirs, successors and assigns as permitted
under the Indenture.

         6. COUNTERPARTS. This Agreement may be executed in one or more
counterparts, each of which shall be deemed an original, but all of which shall
together constitute one and the same instrument.

         7. GOVERNING LAW. This Agreement shall be governed by, and construed
and interpreted in accordance with, the laws of the State of New York.


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         IN WITNESS WHEREOF, this Agreement has been duly executed and delivered
as of the date first written above.



                                           EME HOMER CITY GENERATION L.P.

                                           By: MISSION ENERGY WESTSIDE INC.,
                                               as General Partner


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


                                           EDISON MISSION HOLDINGS CO.


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


                                           THE BANK OF NEW YORK,
                                           As Bondholder Trustee


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


                                           THE BANK OF NEW YORK,
                                           As Collateral Agent


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




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