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                                                                    Exhibit 4.8

                          THIRD SUPPLEMENTAL INDENTURE

         This Third Supplemental Indenture (the "Third Supplemental
Indenture"), dated as of February 25, 1998, is made and entered into by and
between Belco Oil & Gas Corp., a Nevada corporation ("Belco"), the undersigned
Belco Subsidiaries who are, pursuant to this Third Supplemental Indenture,
making a Subsidiary Guarantee (individually, the "Guarantor"), and Chase Bank
of Texas, National Association, formerly known as Texas Commerce Bank National
Association (the "Trustee").

RECITALS

         A. Coda Energy, Inc., a Delaware corporation (the "Company"), was a
party to that certain Indenture, dated as of March 18, 1996 (the "Indenture"),
entered into by and among the Company (as issuer) and Taurus Energy Corp.,
Diamond Energy Operating Company and Electra Resources, Inc. (as guarantors),
and the Trustee (as trustee) providing for the issuance of $110 million in
aggregate principal amount of 10 1/2% Senior Subordinated Notes due 2006 (the
"Notes").

         B. Pursuant to the terms of the Indenture, Taurus Energy Corp. was
released as a guarantor of the Notes upon the sale of Taurus Energy Corp. by
the Company.

         C. Pursuant to a Plan of Merger adopted by the Board of Directors of
Belco, the Company merged with and into Belco, and Belco was the surviving and
successor entity. Pursuant to Section 92A.250 of the Nevada corporate laws, at
the effective time of such merger (the "Effective Time"), Belco acquired all of
the liabilities of the Company.

         D. In order to further evidence the succession of the Company into
Belco and the assumption by Belco of all the obligations of the Company under
the Notes and the Indenture at the Effective Time, and to satisfy the
provisions of Section 5.01 of the Indenture, Belco has previously entered into
a Second Supplemental Indenture with the Trustee dated February 25, 1998,
whereby Belco expressly assumed all of the obligations of the Company under the
Notes and the Indenture.

         E. Pursuant to Section 5.02 of the Indenture, from and after the
Effective Time, the provisions of the Indenture referring to the "Company"
refer to Belco and not to the Company. Section 4.14 of the Indenture requires,
under certain circumstances, the Company to require certain of its
Subsidiaries, who are deemed to make the guarantee set forth in Section 11.01
of the Indenture, to evidence such guarantee in the manner set forth in Section
11.02.

         F. Each of the Guarantors is executing this Third Supplemental
Indenture for the purpose of making the Subsidiary Guarantee contained in
Section 11.01 of the Indenture, pursuant to the terms and conditions of the
Indenture, and complying with Section 11.02 of the Indenture.

         NOW, THEREFORE, Belco, each of the Guarantors and the Trustee agree as
follows:

                  1. Capitalized terms used herein but not defined herein shall
have the meanings assigned to them in the Indenture.

                  2. This Third Supplemental Indenture is being executed and 
delivered pursuant to Sections 4.14 and 11.02.

                  3. Each of the Guarantors makes the Subsidiary Guarantee
contemplated by Section 11.01 of the Indenture, subject to the terms,
conditions and limitations set forth in the Indenture, including but not
limited to those contained in Article 11 of the Indenture.

                  4. This Third Supplemental Indenture is solely for the
benefit of the Trustee and the Holders (as defined in the Indenture) of the
Notes.

                  5. THIS THIRD SUPPLEMENTAL INDENTURE SHALL BE GOVERNED BY AND
CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.





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         IN WITNESS WHEREOF, Belco, each of the Guarantors and the Trustee have
caused this Third Supplemental Indenture to be executed by their respective
officers thereunto duly authorized, as of the date first written above.

                                BELCO OIL & GAS CORP.



Attest:                         By:
                                     ----------------------------------
                                Name:    Robert A. Belfer
-------------------------       Title:   Chairman of the Board; Chief Executive 
                                         Officer


                                CHASE BANK OF TEXAS, NATIONAL ASSOCIATION



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

                                CODA ENERGY, INC.,
                                a Nevada corporation



Attest:                         By:
                                Name:    Grant W. Henderson
-----------------------         Title:   President and Chief Financial Officer

                                BELCO OPERATING CORP.,
                                a Delaware corporation



Attest:                         By:
                                     ---------------------------------
                                Name:
                                     ---------------------------------
-----------------------         Title:            President