<PAGE>
                                                                  EXHIBIT 10.2.1


         FIRST AMENDMENT TO FIFTH AMENDED AND RESTATED CREDIT AGREEMENT

         THIS FIRST AMENDMENT dated as of October 10, 2001 TO FIFTH AMENDED AND
RESTATED CREDIT AGREEMENT (this "First Amendment"), is by and among EL PASO
ENERGY PARTNERS, L.P., a Delaware limited partnership (formerly known AS
LEVIATHAN GAS PIPELINE PARTNERS, L.P., the "Borrower"), EL PASO ENERGY PARTNERS
FINANCE CORPORATION, a Delaware corporation (formerly known as LEVIATHAN FINANCE
CORPORATION, the "Co-Borrower"), CREDIT LYONNAIS NEW YORK BRANCH and FIRST UNION
NATIONAL BANK, as Co-Syndication Agents, FLEET NATIONAL BANK and FORTIS CAPITAL
Corp., as Co-Documentation Agents, THE CHASE MANHATTAN BANK, a New York banking
corporation, as Administrative Agent, and the several banks and other financial
institutions signatories hereto, and shall amend the FIFTH AMENDED AND RESTATED
CREDIT AGREEMENT, dated as of March 23, 1995, as amended and restated through
May 16, 2001 (as amended, supplemented or otherwise modified prior to the date
hereof, the "Credit Agreement"), among the Borrower, the Co-Borrower, the
several banks and other financial institutions (the "Lenders") parties thereto,
Credit Lyonnais New York Branch and First Union National Bank, as Co-Syndication
Agents, Fleet National Bank and Fortis Capital Corp., as Co-Documentation Agents
and The Chase Manhattan Bank, a New York banking corporation, as Administrative
Agent for the Lenders. Unless otherwise defined herein, capitalized terms used
herein shall have the respective meanings assigned to them in the Credit
Agreement and the other Loan Documents (as defined in the Credit Agreement).

         WHEREAS, the Borrower desires to redeem certain of its outstanding
Series B Preference Units with proceeds from a substantially contemporaneous
offering of its Common Units;

         WHEREAS, the Borrower desires to enter into a series of related
transactions with certain subsidiaries of El Paso and certain other entities
with respect to the Chaco cryogenic plant and certain related facilities located
in San Juan County, New Mexico, which transactions are more specifically
described on Exhibit A attached hereto (the "Chaco Transactions");

         WHEREAS, the Borrower desires to correct and clarify certain other
matters related to the Credit Agreement;

         WHEREAS, the Borrower has requested that the Lenders (i) modify and
amend the Credit Agreement as more fully described herein and (ii) waive any and
all violations of or breaches of the Loan Document or Defaults or Events of
Default in connection with the provisions of the Credit Agreement to be amended,
as more fully described herein;

         WHEREAS, the Lenders are willing to agree to the amendments, consents,
waivers and releases being requested by the Borrower, but only on the terms and
subject to the conditions set forth in this First Amendment; and

         WHEREAS, each of the signatories hereto is a party to the Credit
Agreement.

         NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrower, the


                                       1
<PAGE>

Administrative Agent, the Lenders and each of the other signatories hereto
hereby agree as follows:

         1. Amendments. The Amended Loan Documents are hereby amended as
follows:

                  (a) Section 8.7 of the Credit Agreement currently reads as
         follows:

                           Section 8.7 Limitation on Dividends. Declare or pay
                           any dividend or distribution on (other than
                           dividends, including splits, payable solely in
                           non-mandatorily redeemable Capital Stock or
                           mandatorily redeemable Capital Stock that does not
                           require redemption prior to the first anniversary of
                           the Revolving Credit Termination Date), or make any
                           payment on account of, or set apart assets for a
                           sinking or other analogous fund for, the purchase,
                           redemption, defeasance, retirement or other
                           acquisition of, any shares of any class of Capital
                           Stock of the Borrower or any warrants or options to
                           purchase any such Capital Stock, whether now or
                           hereafter outstanding, or make any other distribution
                           in respect thereof, either directly or indirectly,
                           whether in cash or property or in obligations of the
                           Borrower or any Restricted Subsidiary (such
                           declarations, payments, setting apart, purchases,
                           redemptions, defeasances, retirements, acquisitions
                           and distributions being herein called "Restricted
                           Payments"), except that as long as no Default or
                           Event of Default has occurred and is continuing or
                           would result therefrom, the Borrower may make
                           Restricted Payments once each fiscal quarter
                           consisting of cash distributions in accordance with
                           the terms of the Partnership Agreement on its Units
                           and the General Partnership Interest.

         Section 8.7 of the Credit Agreement is amended by adding the following
         sentence to the end thereof:

                           "Notwithstanding anything in this Agreement to the
                           contrary, the Borrower may purchase, redeem, defease,
                           retire or otherwise acquire, or make a distribution
                           in respect of, any of its Series B Preference Units
                           in exchange for, or out of the net cash proceeds of,
                           an issuance of Common Units occurring within 120 days
                           of such purchase, redemption, defeasance, retirement,
                           acquisition, or distribution."

                  (b) Section 1.1 of the Credit Agreement is hereby amended by
         adding the following as a defined term therein:

                           ""Chaco Transactions": The series of related
                  transactions among the Borrower, certain subsidiaries of El
                  Paso and certain other entities with respect to the Chaco
                  cryogenic plant and certain related facilities located in San
                  Juan County, New Mexico, which transactions are more
                  specifically described on Exhibit A attached to the First
                  Amendment dated as of October 10, 2001 to the Credit
                  Agreement.


                                       2
<PAGE>

                  (c) Section 4.13 of the Credit Agreement is hereby amended by
         adding the following as subsection (d) thereof:

                           (d) The consummation by the Borrower and its
                  Subsidiaries of the Chaco Transactions.

                  (d) Section 8.3 of the Credit Agreement is amended as follows:

                      (i) the word "and" is deleted from the end of subsection
                  (i) thereof;

                      (ii) the period at the end of subsection (j) thereof is
                  replaced with a semicolon; and

                      (iii) the following subsections (k) and (l) are added at
                  the end of such section:

                           "(k) Liens securing Indebtedness permitted under
                           Section 8.2(b) to the extent that such Liens arise as
                           a result of the consummation by the Borrower and its
                           Subsidiaries of the Chaco Transactions; and

                           "(l) Liens securing Indebtedness permitted under
                           Section 8.2(f) provided that (i) such Liens are not
                           created in contemplation of or in connection with (A)
                           any Person being merged with or into or becoming a
                           Subsidiary of the Borrower or any Restricted
                           Subsidiary as described in Section 8.2(f)(i),or (B)
                           any asset being acquired by the Borrower or any
                           Restricted Subsidiary as described in Section
                           8.2(f)(ii), as the case may be, (ii) such Liens shall
                           secure only those obligations which such Liens secure
                           on the date on which (A) such Person merges into or
                           becomes a Subsidiary of the Borrower or any
                           Restricted Subsidiary or (B) such asset is acquired
                           by the Borrower or any Restricted Subsidiary, as the
                           case may be, and any refinancing, refunding or
                           replacement of such obligations (provided that such
                           refinancing, refunding or replacement does not result
                           in an increase in the amount of such obligations),
                           and (iii) such Liens shall not apply to any property
                           or assets of the Borrower or any of its Subsidiaries
                           or any Restricted Subsidiary other than property or
                           assets as to which a Lien has been granted prior to
                           the date on which (A) such Person merges into or
                           becomes a Subsidiary or the Borrower or any
                           Restricted Subsidiary or (B) such asset is acquired
                           by the Borrower or any Restricted Subsidiary, as the
                           case may be, and the proceeds thereof."

                  (e) Section 7.13 of the Credit Agreement is hereby amended by
         changing the phrase "Within 60 days of the Closing Date" to "On or
         before January 31, 2002".



                                       3
<PAGE>

         2. Consent and Waiver. The Lenders hereby waive any and all violations
of or breaches of Section 7.13 of the Credit Agreement to the extent occurring
prior to the date hereof.

         3. Conditions to Effectiveness. This First Amendment shall become
effective on the date (the "First Amendment Effective Date") on which all of the
following conditions precedent have been satisfied or waived: (i) the Borrower,
the Co-Borrower, the Administrative Agent and the Required Lenders shall have
executed and delivered to the Administrative Agent this First Amendment and (ii)
the Administrative Agent and the Lenders shall have received payment of all fees
and costs payable by the Borrower on or before the First Amendment Effective
Date in connection with this First Amendment, including an amendment fee of
$5,000 payable to each Lender which delivers an executed copy of this First
Amendment to the Administrative Agent on or before the First Amendment Effective
Date.

         4. Miscellaneous.

                  (a) Representations and Warranties. After giving effect to the
         effectiveness of this First Amendment, the representations and
         warranties made by the Loan Parties in the Loan Documents are true and
         correct in all material respects on and as of the First Amendment
         Effective Date (unless such representations or warranties are stated to
         refer to a specific earlier date, in which case such representations
         and warranties shall be true and correct in all material respects as of
         such earlier date) as if made on and as of the First Amendment
         Effective Date and no Default or Event of Default will have occurred
         and be continuing.

                  (b) Payment of Expenses. The Borrower agrees to pay or
         reimburse the Administrative Agent for all of its out-of-pocket costs
         and reasonable expenses incurred in connection with this First
         Amendment, any other documents prepared in connection herewith and the
         transactions contemplated hereby, including, without limitation, the
         reasonable fees and disbursements of counsel to the Administrative
         Agent.

                  (c) No Other Amendments; Confirmation. Except as expressly
         amended, modified and supplemented hereby, the provisions of the Credit
         Agreement and the other Loan Documents are and shall remain in full
         force and effect.

                  (d) Governing Law. THIS AMENDMENT AND THE RIGHTS AND
         OBLIGATIONS OF THE PARTIES HERETO SHALL BE GOVERNED BY, AND CONSTRUED
         AND INTERPRETED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW YORK.

                  (e) Counterparts. This First Amendment may be executed by one
         or more of the parties to this First Amendment on any number of
         separate counterparts (including by telecopy), and all of said
         counterparts taken together shall be deemed to constitute one and the
         same instrument.


                                   *********


                                       4

<PAGE>
         IN WITNESS WHEREOF, the parties hereto have caused this First Amendment
to be duly executed and delivered as of the day and year first above written.


                                EL PASO ENERGY PARTNERS, L.P.


                                By: /s/ KEITH FORMAN
                                    -------------------------------------------
                                Name:   Keith Forman
                                      -----------------------------------------
                                Title:  Vice President and
                                        Chief Financial Officer
                                      -----------------------------------------


                                EL PASO ENERGY PARTNERS FINANCE CORPORATION


                                By: /s/ KEITH FORMAN
                                    -------------------------------------------
                                Name:   Keith Forman
                                      -----------------------------------------
                                Title:  Vice President and
                                        Chief Financial Officer
                                      -----------------------------------------


                                THE CHASE MANHATTAN BANK,
                                  as Administrative Agent and as a Lender


                                By: /s/ STEVEN WOOD
                                    -------------------------------------------
                                Name:   Steven Wood
                                      -----------------------------------------
                                Title:  Vice President
                                      -----------------------------------------


<PAGE>


                                CREDIT LYONNAIS NEW YORK BRANCH



                                By: /s/ BERNARD WAYMULLER
                                    --------------------------------------------
                                Name:   Bernard Waymuller
                                      ------------------------------------------
                                Title:  Senior Vice President
                                       -----------------------------------------




<PAGE>

                                FLEET NATIONAL BANK



                                By: /s/ CHRISTOPHER C. HOLMGREN
                                    --------------------------------------------
                                Name:   Christopher C. Holmgren
                                      ------------------------------------------
                                Title:  Managing Director
                                       -----------------------------------------



<PAGE>


                                ARAB BANKING CORPORATION (B.S.C.)


                                By: /s/ GRANT E. McDONALD
                                    --------------------------------------------
                                Name:   Grant E. McDonald
                                      ------------------------------------------
                                Title:  Vice President
                                       -----------------------------------------

<PAGE>


                                THE BANK OF NOVA SCOTIA


                                By:      /s/ M.D. SMITH
                                         ---------------------------------------
                                Name:        M.D. Smith
                                         ---------------------------------------
                                Title:       Agent
                                         ---------------------------------------





<PAGE>


                                BANK OF SCOTLAND


                                By:      /s/ JOSEPH FRATUS
                                         ---------------------------------------
                                Name:        Joseph Fratus
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------


<PAGE>


                                BANK ONE, NA


                                By:      /s/ DIANNE RUSSELL
                                         ---------------------------------------
                                Name:        Dianne Russell
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------

<PAGE>


                                BANK OF AMERICA, N.A.


                                By: /s/ MICHAEL J. DILLON
                                   -----------------------------------------
                                Name:   Michael J. Dillon
                                     ---------------------------------------
                                Title:  Managing Director
                                      --------------------------------------


<PAGE>


                                CREDIT AGRICOLE INDOSUEZ


                                By: /s/ BRIAN KNEZEAK
                                   ----------------------------------------
                                Name:   Brian Knezeak
                                     --------------------------------------
                                Title:  FVP, Manager
                                      -------------------------------------


                                By: /s/ MICHAEL D. WILLIS
                                   ----------------------------------------
                                Name:   Michael D. Willis
                                     --------------------------------------
                                Title:  VP, Credit Analysis
                                      -------------------------------------


<PAGE>


                                CREDIT SUISSE FIRST BOSTON


                                By: /s/ JAMES P. MORAN
                                   -----------------------------------------
                                Name:   James P. Moran
                                     ---------------------------------------
                                Title:  Director
                                      --------------------------------------


                                By: /s/ DAVID M. KOCZAN
                                   -----------------------------------------
                                Name:   David M. Koczan
                                     ---------------------------------------
                                Title:  Assistant Vice President
                                      --------------------------------------
<PAGE>


                                THE FUJI BANK, LIMITED


                                By: /s/ TORU MAEDA
                                   -----------------------------------------
                                Name:   Toru Maeda
                                     ---------------------------------------
                                Title:  General Manager
                                      --------------------------------------

<PAGE>


                                FORTIS CAPITAL CORP.


                                By:      /s/ DARRELL HOLLEY
                                         ---------------------------------------
                                Name:        Darrell Holley
                                         ---------------------------------------
                                Title:       Managing Director
                                         ---------------------------------------


                                By:      /s/ CHRIS PARADA
                                         ---------------------------------------
                                Name:        Chris Parada
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------


<PAGE>


                                KBC BANK N.V.


                                By:      /s/ ROBERT SNAUTHER
                                         ---------------------------------------
                                Name:        Robert Snauther
                                         ---------------------------------------
                                Title:       First Vice President
                                         ---------------------------------------


                                By:      /s/ ERIC RASKIN
                                         ---------------------------------------
                                Name:        Eric Raskin
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------


<PAGE>


                                WELLS FARGO BANK TEXAS, N.A.


                                By:      /s/ KAREN PATTERSON
                                         ---------------------------------------
                                Name:        Karen Patterson
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------

<PAGE>


                                BNP PARIBAS


                                By:      /s/ MARK A. COX
                                         ---------------------------------------
                                Name:        Mark A. Cox
                                         ---------------------------------------
                                Title:       Director
                                         ---------------------------------------


                                By:      /s/ LARRY ROBINSON
                                         ---------------------------------------
                                Name:        Larry Robinson
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------
<PAGE>


                                SUNTRUST BANK


                                By:      /s/ STEVE NEWBY
                                         ---------------------------------------
                                Name:        Steve Newby
                                         ---------------------------------------
                                Title:       Vice President
                                         ---------------------------------------


<PAGE>


                                RZB FINANCE LLC


                                By:      /s/ DIETER BEINTREXTER
                                         ---------------------------------------
                                Name:        Dieter Beintrexter
                                         ---------------------------------------
                                Title:       President
                                         ---------------------------------------


                                By:      /s/ FRANK J. YAUTZ
                                         ---------------------------------------
                                Name:        Frank J. Yautz
                                         ---------------------------------------
                                Title:       First Vice President
                                         ---------------------------------------


<PAGE>


                                BAYERISCHE HYPO-UND VEREINSBANK, AG
                                (New York Branch)


                                By: /s/ STEVEN ATWELL
                                    --------------------------------------------
                                Name:   Steven Atwell
                                      ------------------------------------------
                                Title:  Director
                                       -----------------------------------------


                                By: /s/ SHANNON BATCHMAN
                                    --------------------------------------------
                                Name:   Shannon Batchman
                                      ------------------------------------------
                                Title:  Director
                                       -----------------------------------------


<PAGE>


                                THE ROYAL BANK OF SCOTLAND plc, New York Branch


                                By: /s/ KEVIN J. HOWARD
                                    --------------------------------------------
                                Name:   Kevin J. Howard
                                      ------------------------------------------
                                Title:  Managing Director
                                       -----------------------------------------


                                By: /s/ KEVIN J. HOWARD
                                    --------------------------------------------
                                Name:   Kevin J. Howard
                                      ------------------------------------------
                                Title:  Managing Director
                                       -----------------------------------------



<PAGE>


                                CITICORP USA


                                By: /s/ MICHAEL W. NERVEUX
                                    --------------------------------------------
                                Name:   Michael W. Nerveux
                                      ------------------------------------------
                                Title:  Director
                                        Citicorp North America, Inc.
                                       -----------------------------------------
<PAGE>


                                NATEXIS BANQUES POPULAIRES


                                By: /s/ DANIEL PAYER
                                    --------------------------------------------
                                Name:   Daniel Payer
                                      ------------------------------------------
                                Title:  Vice President
                                       -----------------------------------------


                                By: /s/ LOUIS P. LAVILLE, III
                                    --------------------------------------------
                                Name:   Louis P. Laville, III
                                      ------------------------------------------
                                Title:  Vice President and Group Manager
                                       -----------------------------------------

<PAGE>


                                ROYAL BANK OF CANADA


                                By: /s/ TOM J. OBERAIGNER
                                    --------------------------------------------
                                Name:   Tom J. Oberaigner
                                      ------------------------------------------
                                Title:  Senior Manager
                                       -----------------------------------------

<PAGE>

                                    EXHIBIT A
                                       TO
                                 FIRST AMENDMENT
                                       TO
                            EL PASO ENERGY PARTNERS'
                   FIFTH AMENDED AND RESTATED CREDIT AGREEMENT

                             THE CHACO TRANSACTIONS

I.       THE CHACO PLANT

         The Chaco Plant, the third largest natural gas processing plant in the
United States measured by liquids produced, is located in the San Juan Basin in
New Mexico. It is capable of processing up to 600 Mmcf/d of natural gas and
handling up to 50,000 bbls/d of NGLs. The Chaco Plant is a state of the art
cryogenic plant that uses high pressures and extremely low temperatures to
remove water, impurities and excess hydrocarbon liquids from the raw natural gas
stream and recover ethane as well as propane and the heavier hydrocarbons. The
Chaco Plant receives and processes natural gas from the San Juan Gathering
System (the "Gathering System"), an over 5,500 mile natural gas gathering system
in New Mexico owned and operated by an affiliate of El Paso Field Services
("Field Services"). Field Services, directly or through subsidiaries, owns
(beneficially) and operates the Chaco Plant, subject to a sale-leaseback
financing agreement.

II.      TRANSACTION OVERVIEW

         In a series of related transactions, the Partnership (through a
Restricted Subsidiary under the Credit Agreement) will pay approximately $198.5
million to acquire title to and other interests in the Chaco Plant and certain
related rights and interests for the next 20 years; including the dedication of
all uncommitted processing rights that Field Services has with respect to
natural gas gathered by the Gathering System. In addition, Field Services has
agreed to continue to acquire processing rights and dedicate the underlying
natural gas to the Chaco Plant. Natural gas delivered by Field Services will
have first priority on plant capacity. Field Services will pay the Partnership
13.44cents for each Mcf of natural gas processed at the plant by Field Services.
The Partnership will bear all costs of ownership and operations of the Chaco
Plant. Field Services personnel will continue to operate the plant for the
Partnership.

III.     CURRENT STATUS OF CHACO PLANT

         Field Services, through a subsidiary, constructed the Chaco Plant in
1995. Field Services financed a portion of the Chaco Plant construction through
a sale-leaseback transaction in which Field Services sold the Chaco Plant to a
Massachusetts business trust (the "Trust") created by the lenders and leased the
Chaco Plant back from the Trust through October 2002. The transaction
effectively was structured as follows:

         (1)  The lenders capitalized the Trust through a loan and a small
              equity contribution, and were issued notes to evidence the loan
              and certificates to evidence the equity from the Trust;

                                      A-1
<PAGE>

         (2)  The Trust purchased the Chaco Plant using the lenders' investment
              and loaned funds, and granted liens covering the Chaco Plant in
              favor of the lenders;

         (3)  The Trust leased the Chaco Plant back to Field Services;

         (4)  Field Services has the obligation to operate the Chaco Plant;

         (5)  Field Services has the right to repurchase the plant in October
              2002 for approximately $72 million; and

         (6)  If Field Services does not exercise its repurchase right, it has
              to pay a substantial forfeiture payment to the Trust.

State Street Bank and Trust Company is currently the trustee of the Trust.

IV.      THE CURRENTLY CONTEMPLATED CHACO TRANSACTIONS

         In order for the Partnership's Restricted Subsidiary to acquire its
interests in the Chaco Plant, the following transactions will occur:

         (1)  The Partnership will acquire title to the Plant, subject to the
              Chaco lease documents, by becoming the beneficiary of the Trust
              through the purchase of the notes and certificates issued by the
              Trust to the sale-leaseback lenders;

         (2)  The Restricted Subsidiary will become agent for the Trust;

         (3)  Another Restricted Subsidiary will become trustee of the Trust;

         (4)  The Trust will become a Restricted Subsidiary and, accordingly,
              will guarantee the indebtedness outstanding under the Credit
              Agreement and pledge its assets as collateral for the Credit
              Agreement;

         (5)  The Restricted Subsidiary and Field Services will enter into a
              Tolling Agreement under which (a) Field Services will dedicate all
              of the natural gas received into the Gathering System to the Chaco
              Plant for processing (except for certain amounts of natural gas
              that have previously been dedicated to the nearby Conoco/Blanco
              Plant, and certain other amounts of natural gas that will be used
              for fuel use, farm taps and lift gas, or temporarily offloaded due
              to capacity constraints on the Gathering System pursuant to terms
              of existing gathering agreements), (b) Field Services will be
              obligated to attempt to acquire additional processing rights for
              gas gathered by the Gathering System, (c) gas delivered to the
              Chaco Plant by Field Services will have a processing priority over
              other gas; and

         (6)  Field Services personnel will continue to operate and provide
              other services related to the Chaco Plant.


                                      A-2