<PAGE>   1
                                                                   EXHIBIT 10-CR

                                U.S. $850,000,000

               THIRD AMENDED AND RESTATED 364-DAY CREDIT AGREEMENT


                          Dated as of October 11, 2000

                                      among

                             COLUMBIA ENERGY GROUP,


                                  as Borrower,

                                       and

                            THE LENDERS NAMED HEREIN,


                                   as Lenders,

                                       and

                           SALOMON SMITH BARNEY INC.,


                          as Arranger and Book Manager,

                                       and

                                 CITIBANK, N.A.,


                    as Administrative and Syndication Agent,

                                       and

                          THE CHASE MANHATTAN BANK AND

                           FIRST UNION NATIONAL BANK,
                            as Documentation Agents,

                                       and

                           BANK ONE, N.A., THE BANK OF
  NOVA SCOTIA, PNC BANK, NATIONAL ASSOCIATION, COMMERZBANK AG, NEW YORK BRANCH
                               as Managing Agents
<PAGE>   2
                                       and

          CREDIT AGRICOLE INDOSUEZ AND DEUTSCHE BANK AG NEW YORK BRANCH

                                  as Co-Agents
<PAGE>   3
                           THIRD AMENDED AND RESTATED

                            364-DAY CREDIT AGREEMENT


Dated as of October 11, 2000

                  This THIRD AMENDED AND RESTATED 364-DAY CREDIT AGREEMENT (this
"Amendment and Restatement") among COLUMBIA ENERGY GROUP, a Delaware corporation
(the "Borrower"), the banks, financial institutions and other institutional
lenders parties to the Credit Agreement referred to below (collectively, the
"Lenders"), and SALOMON SMITH BARNEY INC., as arranger and book manager
("Arranger and Book Manager"), and CITIBANK, N.A. ("Citibank"), as
administrative and syndication agent (the "Agent") for the Lenders, evidences
the agreement of the parties as follows:

                  PRELIMINARY STATEMENTS:

                  The Borrower, the Lenders and the Agent have entered into a
Second Amended and Restated 364-Day Credit Agreement dated as of March 8, 2000
(as amended, amended and restated, supplemented or otherwise modified through
the date hereof, the "Credit Agreement"). Capitalized terms not otherwise
defined in this Amendment and Restatement have the same meanings as specified in
the Credit Agreement.

                  The Borrower and the Lenders have agreed to amend the Credit
Agreement as hereinafter set forth and to restate the Credit Agreement in its
entirety to read as set forth in the Credit Agreement with the amendments
specified below.

Amendments to Credit Agreement. The Credit Agreement, effective as of the date
hereof and, subject to the satisfaction of the conditions precedent set forth in
Section 3.02, is hereby amended as follows:

Section 1.01 is hereby amended by amending in full the proviso clause appearing
at the end of the definition of "Tangible Net Worth" to read "provided, however,
that notwithstanding the foregoing exclusions, (A) regulatory assets recorded on
the Consolidated balance sheet of the Borrower and its Subsidiaries, and (B) any
acquisition goodwill which may appear on the Consolidated balance sheet of the
Borrower and its Subsidiaries resulting from the NiSource Merger shall not be
excluded for purposes of determining Tangible Net Worth."

Section 1.01 is hereby amended by (i) deleting the definitions of "Five-Year
Credit Agreement," "Five-Year Loan Documents" and "Five-Year Notes," (ii)
amending in full certain existing definitions appearing therein as set forth
below, and (iii) adding new definitions thereto to read as follows:

                         "Advance" means a Revolving Credit Advance and a Swing
                  Line Advance.

                         "Appropriate Lender" means, at any time, with respect
                  to (a) the Revolving Credit Facility, a Lender that has a
                  Revolving Credit Commitment with respect to such Facility at
                  such time, and (b) the Swing Line Facility, a Swing Line Bank
                  that has a Swing Line Commitment.

                         "Borrowing" means a Revolving Credit Borrowing or a
                  Swing Line Borrowing.

                         "Facility" means the Revolving Credit Facility or the
                  Swing Line Facility.
<PAGE>   4
                           "Information Memorandum" means the information
                  memorandum dated September 2000 used by the Arranger and Book
                  Manager in connection with the syndication of the Revolving
                  Credit Commitments.

                           "Initial Swing Line Bank" means either Citibank or
                  PNC Bank.

                           "Lenders" means the Initial Lenders, the Initial
                  Swing Line Bank and each Person that shall become a Party
                  hereto pursuant to Section 8.07(a), (b) and (c).

                           "NiSource Merger" means a series of mergers, as a
                  result of which the Borrower will become a wholly owned
                  subsidiary of NiSource, Inc., an Indiana corporation
                  ("NiSource"), as contemplated under the terms of the NiSource
                  Merger Agreement.

                           "NiSource Merger Agreement" means a Merger Agreement
                  dated as of February 27, 2000 (as amended, amended and
                  restated or otherwise modified to the date hereof) between the
                  Borrower and NiSource.

                           "Note" means a Revolving Credit Note or a Swing Line
                  Note.

                           "Notice of Swing Line Borrowing" has the meaning
                  specified in Section 2.02(f).

                           "Pro Rata Share" of any amount means, with respect to
                  any Lender or any Swing Line Bank, as the case may be, at any
                  time, the product of such amount times, in the case of a
                  Lender, a fraction the numerator of which is the amount of
                  such Lender's Revolving Credit Commitment at such time and the
                  denominator of which is the aggregate amount of the Revolving
                  Credit Commitments of all Lenders at such time, in the case of
                  a Swing Line Bank, a fraction the numerator of which is the
                  amount of such Swing Line Bank's Swing Line Commitment and the
                  denominator of which is the aggregate amount of the Swing Line
                  Commitments of all Swing Line Banks at such time.

                           "Swing Line Advance" means an advance made by a Swing
                  Line Bank pursuant to Section 2.01(b).

                           "Swing Line Banks" means Citibank, PNC Bank and such
                  other Lenders mutually acceptable to the Borrower and the
                  Agent.

                           "Swing Line Borrowing" means a Borrowing consisting
                  of a Swing Line Advance made by a Swing Line Bank.

                           "Swing Line Commitment" has the meaning specified in
                  Section 2.01(b).

                           "Swing Line Cost of Funds Advance" means a Swing Line
                  Advance which shall bear interest, during such periods as such
                  Swing Line Advance is a Swing Line Cost of Funds Advance, at a
                  rate per annum equal, at all times during each Interest Period
                  for such Swing Line Advance, to the sum of (i) the weighted
                  average cost per annum of funds as reasonably determined by
                  each Swing Line Bank making such Advance plus (ii) the greater
                  of (a) 1.00% per annum or (b) two times the sum of (x) the
                  Applicable Margin then in effect for Eurodollar Rate Advances
                  plus (y) the applicable Margin then in effect for the Facility
                  Fee.

                           "Swing Line Facility" has the meaning specified in
                  Section 2.01(b).
<PAGE>   5
                           "Swing Line Note" means a promissory note of the
                  Borrower payable to the order of a Swing Line Bank, in
                  substantially the form of Exhibit AA hereto, evidencing the
                  Swing Line Advances made by such Swing Line Bank.

                           "Termination Date" means the earlier of (a) October
                  10, 2001 or, if extended pursuant to Section 2.16(a), the date
                  that is 364 days after the Termination Date then in effect,
                  and (b) the date of termination in whole of the Revolving
                  Credit Commitments pursuant to Section 2.03 or 6.01.

                           "Two-Year Credit Agreement" means the Amended and
                  Restated Credit Agreement dated as of October 11, 2000 among
                  the Borrower, the Agent and the lenders named therein.

                           "Two-Year Loan Documents" means the Two-Year Credit
                  Agreement and the Two-Year Notes.

                           "Two-Year Notes" means each of the promissory notes
                  of the Borrower executed pursuant to the Two-Year Credit
                  Agreement.

                           "Unused Revolving Credit Commitment" means, at any
                  time, (a) the aggregate Revolving Credit Commitment at such
                  time, minus (b) the sum, without duplication, of (i) the
                  aggregate principal amount of all Revolving Credit Advances
                  made by all Lenders and outstanding at such time, and (ii) the
                  aggregate principal amount of all Swing Ling Advances
                  outstanding at such time.

The chart contained in the definition of "Applicable Margin" in Section 1.01 is
amended in full to read as set forth on Exhibit A hereto.

Section 2.01 is amended by (i) inserting a new section heading "The Advances" in
the first line thereof, (ii) inserting "(a)" before the former heading "The
Revolving Credit Advances" in the first line thereof, and (iii) adding a new
subsection (b) thereto to read as follows:

                           "(b) The Swing Line Advances. Each Swing Line Bank
                  severally agrees, on the terms and conditions hereinafter set
                  forth, to make Swing Line Advances to the Borrower from time
                  to time on any Business Day from the Effective Date until the
                  Termination Date in an aggregate amount which shall not exceed
                  at any time outstanding the amount set opposite such Swing
                  Line Bank's name on the signature pages hereof under the
                  caption "Swing Line Commitments" (such amount being such Swing
                  Line Bank's "Swing Line Commitment"); provided, however, that
                  the aggregate amount of all Swing Line Advances outstanding at
                  any time shall not exceed $127,500,000 (the "Swing Line
                  Facility") and, provided further that no Swing Line Borrowing
                  shall be made if, following the making of such Swing Line
                  Borrowing, either (i) the Unused Revolving Credit Commitments
                  of the Lenders shall be less than the aggregate unpaid
                  principal amount of the Swing Line Advances or (ii) the
                  aggregate amount of the Advances then outstanding would exceed
                  the aggregate amount of the Revolving Credit Commitments of
                  the Lenders. No Swing Line Advance shall be used for the
                  purpose of funding the payment of principal of any other Swing
                  Line Advance. Each Swing Line Borrowing shall be in an amount
                  of $100,000 or an integral multiple of $10,000 in excess
                  thereof and shall be made, at the determination of the
                  Borrower, either (i) as a Base Rate Advance, (ii) as a Swing
                  Line Cost of Funds Advance or (iii) as an Advance bearing
                  interest as the Borrower and the Applicable Swing Line Bank
                  shall otherwise agree. The
<PAGE>   6
                  terms and conditions of the Swing Line Commitment of any Swing
                  Line Bank and the Swing Line Advances made by any such Swing
                  Line Bank (other than terms and conditions relating to the
                  amount of the Swing Line Commitment, interest rate, tenor or
                  term of any such Swing Line Advance) may be modified from the
                  terms and conditions provided herein upon mutual agreement of
                  the Borrower and such Swing Line Bank. Within the limits of
                  the Swing Line Facility and within the limits referred to in
                  this Section 2.01(b), the Borrower may borrow under this
                  Section 2.01(b), repay pursuant to Section 2.04(b) or prepay
                  pursuant to Section 2.09 and reborrow under this Section
                  2.01(b)."

Section 2.02 is amended by adding a new subsection (f) at the end thereof to
read as follows:

                           "(f) Each Swing Line Borrowing shall be made on
                  notice, given not later than 2:00 P.M. (New York City time),
                  or such later time as agreed to by the Borrower and the
                  applicable Swing Line Bank, on the date of the proposed Swing
                  Line Borrowing, by the Borrower to the applicable Swing Line
                  Bank and the Agent. Each such notice of a Swing Line Borrowing
                  (a "Notice of Swing Line Borrowing") shall be by telephone,
                  confirmed immediately in writing, or tested telex or
                  telecopier, specifying therein the requested (i) date of such
                  Swing Line Borrowing, (ii) amount of such Swing Line Borrowing
                  and (iii) maturity of such Swing Line Borrowing (which
                  maturity shall be no later than the tenth day after the
                  requested date of such Borrowing). The applicable Swing Line
                  Bank will make the amount of each Swing Line Advance available
                  to the Agent at the Agent's Account, in same day funds or make
                  such amount available to the Borrower as agreed between such
                  applicable Swing Line Bank and the Borrower. Upon written
                  demand to the Agent (who shall promptly notify each other
                  Lender) by any Swing Line Bank with an outstanding Swing Line
                  Advance, each other Lender shall purchase from such Swing Line
                  Bank, and such Swing Line Bank shall sell and assign to each
                  such other Lender, such other Lender's Pro Rata Share of such
                  outstanding Swing Line Advance as of the date of such demand,
                  by making available for the account of its Applicable Lending
                  Office to the Agent for the account of such Swing Line Bank,
                  by deposit to the Agent's Account, in same day funds, an
                  amount equal to the portion of the outstanding principal
                  amount of such Swing Line Advance to be purchased by such
                  Lender. The Borrower hereby agrees to each such sale and
                  assignment. Each Lender unconditionally agrees to purchase its
                  Pro Rata Share of an outstanding Swing Line Advance on (i) the
                  Business Day on which demand therefor is made by the Swing
                  Line Bank that made such Advance, provided that notice of such
                  demand is given not later than 11:00 A.M. (New York City time)
                  on such Business Day or (ii) the first Business Day next
                  succeeding such demand if notice of such demand is given after
                  such time. Upon any such assignment by a Swing Line Bank to
                  any other Lender of a portion of a Swing Line Advance, such
                  Swing Line Bank represents and warrants to such other Lender
                  that such Swing Line Bank is the legal and beneficial owner of
                  such interest being assigned by it, but makes no other
                  representation or warranty and assumes no responsibility with
                  respect to such Swing Line Advance, the Loan Documents, the
                  Borrower or any of its Subsidiaries. If and to the extent that
                  any Lender shall not have so made the amount of such Swing
                  Line Advance available to the Agent, such Lender agrees to pay
                  to the Agent forthwith on demand such amount together with
                  interest thereon, for each day from the date of demand by such
                  Swing Line Bank until the date such amount is paid to the
                  Agent, at the Federal Funds Rate. If such Lender shall pay to
                  the Agent such amount for the account of such Swing Line Bank
                  on any Business Day, such amount so paid in respect of
                  principal shall constitute a Swing Line Advance made by such
                  Lender on such Business Day for purposes of this Agreement,
                  and the outstanding principal amount of the Swing
<PAGE>   7
                  Line Advance made by such Swing Line Bank shall be reduced by
                  such amount on such Business Day. The obligation of each other
                  Lender to purchase a pro-rata share of any Swing Line Bank's
                  Swing Line Advances is absolute and unconditional
                  notwithstanding the occurrence of any circumstances,
                  including, without limitation, any Event of Default, set-off
                  or deduction by the Borrower or its Subsidiaries."

Section 2.04 is amended by (i) inserting a new section heading "Repayment of
Advances" in the first line thereof, (ii) inserting "(a)" before the former
heading "Repayment of Revolving Credit Advances" in the first line thereof, and
(iii) adding a new subsection (b) thereto to read as follows:

                           "(b) Repayment of Swing Line Advances. The Borrower
                  shall repay to each Lender that has made a Swing Line Advance
                  the outstanding principal amount of each Swing Line Advance
                  made by each of them (together with interest thereon) on the
                  earlier of the maturity date specified in the applicable
                  Notice of Swing Line Borrowing (which maturity shall be no
                  later than the tenth day after the requested date of such
                  Borrowing) and the Termination Date."

Section 2.07(e) is amended by deleting the figure "33 1/3%" in the second line
thereof and substituting "25%" therefor.

Section 2.09 is amended in full to read as follows:

                           "Section 2.09. Prepayments of Advances. Optional. The
                  Borrower may, upon (i) at least three Business Days' notice,
                  in the case of a Eurodollar Rate Advance or CD Rate Advance,
                  (ii) at least one Business Day's notice, in the case of a Base
                  Rate Advance, and (iii) same day notice, in the case of a
                  Swing Line Advance, in each case to the Agent, stating the
                  proposed date and aggregate principal amount of the
                  prepayment, and, if such notice is given, the Borrower shall,
                  prepay the outstanding principal amount of such Advances
                  comprising part of the same Borrowing in whole or ratably in
                  part, together with accrued interest to the date of such
                  prepayment on the principal amount prepaid; provided, however,
                  that (x) each partial prepayment shall be in an aggregate
                  principal amount of $10,000,000 or an integral multiple of
                  $1,000,000 in excess thereof (or, in the case of Swing Line
                  Advances, the full amount of any such Swing Line Advance);
                  provided, however, that, following each partial prepayment of
                  any Eurodollar Rate Advance, the remaining outstanding amount
                  of such Advance shall be at least $10,000,000 and (y) in the
                  event of any such prepayment of a Eurodollar Rate Advance or
                  CD Rate Advance other than on the last day of the Interest
                  Period therefor, the Borrower shall be obligated to reimburse
                  the Lenders in respect thereof pursuant to Section 8.04(c).

                           (b) Mandatory. The Borrower shall, on each Business
                  Day, prepay an aggregate principal amount of the Revolving
                  Credit Advances comprising part of the same Borrowings and the
                  Swing Line Advances equal to the amount by which (A) the sum
                  of the aggregate principal amount of (x) the Revolving Credit
                  Advances and (y) the Swing Line Advances then outstanding
                  exceeds (B) the Revolving Credit Facility on such Business
                  Day.

                           (i) Prepayments made pursuant to this subsection (b)
                  shall be, first, applied to prepay Swing Line Advances then
                  outstanding until such Advances are paid in full and, second,
                  applied to prepay Revolving Credit Advances then outstanding
                  comprising part of the same Borrowings until such Advances are
                  paid in full.
<PAGE>   8
                           (ii) All prepayments under this subsection (b) shall
                  be made together with accrued interest to the date of such
                  prepayment on the principal amount prepaid. If any payment
                  required to be made under this Section 2.09(b) on account of
                  Eurodollar Rate Advances or CD Rate Advances would be made
                  other than on the last day of the applicable Interest Period
                  therefor, the Borrower may, in lieu of prepaying such Advance,
                  deposit the amount of such payment in the Cash Collateral
                  Account until the last day of the applicable Interest Period
                  at which time such payment shall be made."

Section 2.16(b) is hereby deleted in its entirety.

Section 3.01(a) is amended by deleting the reference to "December 31, 1998" and
substituting "December 31, 1999" therefor.

Section 3.01(h) is amended in full to read as follows:

                           "(h) The Agent shall have received, on or before the
                  Effective Date, the following, each dated such day, in form
                  and substance satisfactory to the Agent and (except for the
                  Revolving Credit Notes and the Swing Line Notes) in sufficient
                  copies for each Lender:

The Revolving Credit Notes to the order of the Lenders and the Swing Line Notes
to the order of the Swing Line Banks, respectively."

Section 4.01(e) is amended by (i) deleting the reference to "December 31, 1998"
in each place in which it appears and substituting "December 31, 1999" therefor,
(ii) deleting the reference to "September 30, 1999" in each place in which it
appears and substituting "June 30, 2000" therefor, and (iii) deleting the word
"nine" in the sixth and eighth lines thereof and substituting "six" therefor.

 Section 5.02(b) is amended by adding the following proviso clause after the
phrase "the Revolving Credit Commitments)" in the fifth line thereof to read
"provided that the foregoing provisions of this Section 5.02(b) shall not be
applicable to the NiSource Merger, and further."

Section 6.01(h) is amended by adding the following proviso clause after the word
"Borrower" in the last line thereof to read "; provided, however, that the
foregoing provisions of this Section 6.01(h) shall not be applicable to the
NiSource Merger."

The Commitments are amended in full to read as set forth on Schedule I hereto.

Conditions of Effectiveness. This Amendment and Restatement shall become
effective as of the date first above written when, and only when, the Agent
shall have received counterparts of this Amendment and Restatement executed by
the Borrower and all of the Lenders that have a Commitment greater than $0 on
Schedule I or, as to any of the Lenders, advice satisfactory to the Agent that
such Lender has executed this Amendment and Restatement, and when the Agent
shall have additionally received all of the following documents, each such
document (unless otherwise specified) dated the date of receipt thereof by the
Agent (unless otherwise specified) and (except for the Revolving Credit Notes
and the Swing Line Notes) in sufficient copies for each Lender, in form and
substance satisfactory to the Agent (unless otherwise specified):

The new Revolving Credit Notes and the Swing Line Notes issued in connection
with this Amendment and Restatement to the order of each of the Lenders that has
a Commitment in a different amount from that with respect to the Credit
Agreement.
<PAGE>   9
Certified copies of (i) the resolutions of the Board of Directors of the
Borrower approving (or authorizing the transactions encompassed by) this
Amendment and Restatement and (ii) all documents evidencing other necessary
corporate action and governmental approvals, if any, with respect to this
Amendment and Restatement.

A certificate of the Secretary or an Assistant Secretary of the Borrower
certifying the names and true signatures of the officers of the Borrower
authorized to sign this Amendment and Restatement and the other documents to be
delivered hereunder.

A favorable opinion of LeBoeuf, Lamb, Greene & MacRae, L.L.P., counsel for the
Borrower, in substantially the form of Exhibit B hereto.

A favorable opinion of Shearman & Sterling, counsel for the Agent, in form and
substance satisfactory to the Agent.

A certificate signed by a duly authorized officer of the Borrower stating that:

The representations and warranties contained in Section 4.01 of the Credit
Agreement and in Section 3 hereof are correct on and as of the date of such
certificate as though made on and as of such date; and

No event has occurred and is continuing that constitutes a Default.

Representations and Warranties of the Borrower. The Borrower represents and
warrants as follows:

The execution, delivery and performance by the Borrower of this Amendment and
Restatement are within the Borrower's corporate powers, have been duly
authorized by all necessary corporate action and do not contravene (i) the
Borrower's charter or by-laws or (ii) any law or any contractual restriction
binding on or affecting the Borrower, except where such contravention would not
be reasonably likely to have a Material Adverse Effect.

No authorization or approval or other action by, and no notice to or filing
with, any governmental authority or regulatory body or any other third party is
required for the due execution, delivery or performance by the Borrower of this
Amendment and Restatement, except where the Borrower's failure to receive, take
or make such authorization, approval, action, notice or filing would not have a
Material Adverse Effect.

This Amendment and Restatement has been duly executed and delivered by the
Borrower. This Amendment and Restatement is a legal, valid and binding
obligation of the Borrower, enforceable against the Borrower in accordance with
its terms, subject to applicable bankruptcy, reorganization, insolvency,
moratorium or similar laws affecting creditors' rights generally and general
principles of equity.

Reference to and Effect on the Credit Agreement. On and after the effectiveness
of this Amendment and Restatement, each reference in the Credit Agreement to
"this Agreement", "hereunder", "hereof" or words of like import referring to the
Credit Agreement, shall mean and be a reference to the Credit Agreement, as
amended and restated by this Amendment and Restatement; provided, however, that
the word "hereafter" appearing in the definition of "Material Subsidiaries" in
Section 1.01 shall refer to the period after March 11, 1998. Each Lender on
Schedule I with a Commitment of "$0" shall cease to be a party to the Credit
Agreement.

The Credit Agreement, as specifically amended and restated by this Amendment and
Restatement, is and shall continue to be in full force and effect and is hereby
in all respects ratified and confirmed.
<PAGE>   10
The execution, delivery and effectiveness of this Amendment and Restatement
shall not, except as expressly provided herein, operate as a waiver of any
right, power or remedy of any Lender or the Agent under the Credit Agreement,
nor constitute a waiver of any provision of the Credit Agreement.

Costs, Expenses, Etc. The Borrower agrees to pay on demand all costs and
expenses of the Agent in connection with the preparation, execution, delivery
and administration, modification and amendment of this Amendment and Restatement
and the other instruments and documents to be delivered hereunder (including,
without limitation, the reasonable fees and expenses of counsel for the Agent)
in accordance with the terms of Section 8.04 of the Credit Agreement. The Agent
agrees to request as promptly as practicable from (a) Lenders whose Revolving
Credit Notes or the Swing Line Notes, as the case may be, are being replaced
pursuant to this Amendment and Restatement as of the date hereof, and (b)
Lenders who shall have ceased to be parties to the Credit Agreement as of the
date hereof, the return of their old Revolving Credit Notes or the Swing Line
Notes, as the case may be. The Agent agrees to release any new Revolving Credit
Note or the Swing Line Notes, as the case may be, payable to a Lender only upon
the return of the old Revolving Credit Note or the Swing Line Notes, as the case
may be, payable to such Lender.

Execution in Counterparts. This Amendment and Restatement may be executed in any
number of counterparts and by different parties hereto in separate counterparts,
each of which when so executed shall be deemed to be an original and all of
which taken together shall constitute but one and the same agreement. Delivery
of an executed counterpart of a signature page to this Amendment and Restatement
by telecopier shall be effective as delivery of an original executed counterpart
of this Amendment and Restatement.

Governing Law. This Amendment and Restatement shall be governed by, and
construed in accordance with, the laws of the State of New York.

IN WITNESS WHEREOF, the parties hereto have caused this Amendment and
Restatement to be executed by their respective officers thereunto duly
authorized, as of the date first above written.

                 COLUMBIA ENERGY GROUP

                 By     /s/ Michael W. O'Donnell
                        ------------------------
                        Name: Michael W. O'Donnell
                        Title: Senior Vice President and Chief Financial Officer


                 SALOMON SMITH BARNEY INC.,
                    as Arranger and Book Manager

                 By     /s/ Steven R. Veterin
                        ---------------------
                        Name: Steven R. Veterin
                        Title: Managing Director


                 CITIBANK, N.A.,
                    as Administrative and Syndication Agent

                 By     /s/ Steven M. Baillie
                        ---------------------
                        Name: Steven M. Baillie
                        Title: Attorney in Fact
<PAGE>   11
Lenders

                 CITIBANK, N.A.

                 By     /s/ Steven M. Baillie
                        ---------------------
                        Name: Steven M. Baillie
                        Title: Attorney in Fact

                 Amount of Revolving Credit Commitment
                 $75,000,000.00

                 Amount of Swing-line Commitment
                 $127,500,000.00


                 THE CHASE MANHATTAN BANK

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

                 Amount of Revolving Credit Commitment
                 $75,000,000.00


                 FIRST UNION NATIONAL BANK

                 By     /s/ Michael J. Kolosowsky
                        -------------------------
                        Name:  Michael J. Kolosowsky
                        Title: Vice President

                 Amount of Revolving Credit Commitment
                 $75,000,000.00


                 THE BANK OF NOVA SCOTIA

                 By     /s/ P. C. B. Ashby
                        ------------------
                        Name:  P. C. B. Ashby
                        Title: Senior Manager Loan Operations

                 Amount of Revolving Credit Commitment
                 $62,500,000.00
<PAGE>   12
                 BANK ONE, NA

                 By     /s/ George R. Schanz
                        --------------------
                        Name:  George R. Schanz
                        Title: First Vice President

                 Amount of Revolving Credit Commitment
                 $62,500,000.00


                 COMMERZBANK AG, NEW YORK BRANCH

                 By     /s/ Timothy Chin
                        ----------------
                        Name:  Timothy Chin
                        Title: Vice President

                 By     /s/ Andrew Kjoller
                        ------------------
                        Name:  Andrew Kjoller
                        Title: Assistant Vice President

                 Amount of Revolving Credit Commitment
                 $62,500,000.00


                 PNC BANK, NATIONAL ASSOCIATION

                 By     /s/ Brian M. Begg
                        -----------------
                        Name:  Brian M. Begg
                        Title: Director

                 Amount of Revolving Credit Commitment
                 $62,500,000.00

                 Amount of Swing-line Commitment
                 $127,500,000.00


                 CREDIT AGRICOLE INDOSUEZ

                 By     /s/ Brian D. Knezeak
                        --------------------
                        Name:  Brian D. Knezeak
                        Title: First Vice President


                  By    /s/ Michael Willis
                        ------------------
                        Name:  Michael Willis
                        Title: Vice President Credit Analysis

                   Amount of Revolving Credit Commitment
                   $50,000,000.00
<PAGE>   13
                   DEUTSCHE BANK AG NEW YORK AND/OR CAYMAN ISLANDS BRANCHES

                   By   /s/ Belinda J. Wheeler
                        ----------------------
                        Name:  Belinda J. Wheeler
                        Title: Vice President

                   By   /s/ Catherine Ruhland
                        ---------------------
                        Name:  Catherine Ruhland
                        Title: Vice President

                    Amount of Revolving Credit Commitment
                    $50,000,000.00


                    ALL FIRST BANK

                    By  /s/ Stefan Hoenicke
                        -------------------
                        Name:  Stefan Hoenicke
                        Title: Vice President

                    Amount of Revolving Credit Commitment
                    $37,500,000.00


                    ARAB BANK, PLC

                    By  /s/ Samer Tamimi
                        ----------------
                        Name:  Samer Tamimi
                        Title: Vice President

                    Amount of Revolving Credit Commitment
                    $37,500,000.00


                    BANCA MONTE DEI PASCHI DI SIENA S.p.A.

                    By  /s/ Giulio Natalicchi
                        ------------------------
                        Name:  Giulio Natalicchi
                        Title: Senior Vice President and General Manager

                    By  /s/ Brian Landy
                        ---------------
                        Name:  Brian Landy
                        Title: Vice President

                    Amount of Revolving Credit Commitment
                    $37,500,000.00
<PAGE>   14
                    BANK OF MONTREAL

                    By  /s/ Ian M. Plester
                        ------------------
                        Name:  Ian M. Plester
                        Title: Director

                    Amount of Revolving Credit Commitment
                    $37,500,000.00


                    NATIONAL CITY BANK

                    By  /s/ William J. Whitley
                        ------------------------
                        Name:  William J. Whitley
                        Title: Senior Vice President

                    Amount of Revolving Credit Commitment
                    $37,500,000.00


                    SUNTRUST BANK

                    By  /s/ Nancy R. Petrash
                        --------------------
                        Name:  Nancy R. Petrash
                        Title: Director Corporate and Investment Banking

                    Amount of Revolving Credit Commitment
                    $37,500,000.00


                    BANK OF TOKYO-MITSUBISHI TRUST COMPANY

                    By  /s/ Nicholas R. Battista
                        ------------------------
                        Name:  Nicholas R. Battista
                        Title: Vice President

                    Amount of Revolving Credit Commitment
                    $28,000,000.00


                    UNION BANK OF CALIFORNIA

                    By  /s/ David M. Musicant
                        ---------------------
                           Name:  David M. Musicant
                           Title: Vice President

                    Amount of Revolving Credit Commitment
                    $22,000,000.00
<PAGE>   15
<TABLE>
<CAPTION>
                                                             SCHEDULE I

------------------------------------------------------------------------------------------------------------------------------------
                                                                                                      AMOUNT OF     AMOUNT OF SWING
    NAME OF INITIAL LENDER          DOMESTIC LENDING OFFICE          EURODOLLAR LENDING OFFICE        COMMITMENT    LINE COMMITMENT
------------------------------------------------------------------------------------------------------------------------------------
<S>                             <C>                               <C>                               <C>                <C>
Citibank, N.A.                    2 Allen Center, 20th Floor        2 Allen Center, 20th Floor      $75,000,000         $127,500,000
                                       1200 Smith Street                 1200 Smith Street
                                       Houston, TX 77002                 Houston, TX 77002
                                         Steve Baillie                     Steve Baillie
                                       Tel: 713-654-2887                 Tel: 713-654-2887
                                       Fax: 713-654-2849                 Fax: 713-654-2849
------------------------------------------------------------------------------------------------------------------------------------
The Chase Manhattan Bank          270 Park Avenue-21st Floor        270 Park Avenue-21st Floor      $75,000,000              $0
                                    New York, NY 10017-2070           New York, NY 10017-2070
                                          Steve Wood                        Steve Wood
                                       Tel: 212-270-7056                 Tel: 212-270-7056
                                       Fax: 212-270-3897                 Fax: 212-270-3897
------------------------------------------------------------------------------------------------------------------------------------
First Union National Bank           One First Union Center            One First Union Center        $75,000,000              $0
                                   301 South College Street          301 South College Street
                                   Charlotte, NC 28288-0735          Charlotte, NC 28288- 0735
                                        Chanue Michael                    Chanue Michael
                                       Tel: 704-715-1195                 Tel: 704-715-1195
                                       Fax: 704-383-7999                 Fax: 704-383-7999
------------------------------------------------------------------------------------------------------------------------------------
The Bank of Nova Scotia             600 Peachtree Street NE           600 Peachtree Street NE       $62,500,000              $0
                                          Suite 2700                        Suite 2700
                                       Atlanta, GA 30308                 Atlanta, GA 30308
                                      Anthony Millington                Anthony Millington
                                       Tel: 404-877-1579                 Tel: 404-877-1579
                                       Fax: 404-888-8998                 Fax: 404-888-8998
------------------------------------------------------------------------------------------------------------------------------------
Bank One, NA                           1 Bank One Plaza                  1 Bank One Plaza           $62,500,000              $0
                                   Mail Stop IL1 Suite 0363          Mail Stop IL1 Suite 0363
                                         Kenneth Bauer                     Kenneth Bauer
                                       Tel: 312-732-6282                 Tel: 312-732-6282
                                       Fax: 312-732-3055                 Fax: 312-732-3055
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   16
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
<S>                             <C>                               <C>                               <C>                <C>


Commerzbank AG,                    2 World Financial Center          2 World Financial Center       $62,500,000              $0
New York Branch                     New York, NY 10281-1050           New York, NY 10281-1050
                                        Barbara Stacks                    Barbara Stacks
                                       Tel: 212-266-7313                 Tel: 212-266-7313
                                       Fax: 212-266-7235                 Fax: 212-266-7235
------------------------------------------------------------------------------------------------------------------------------------
PNC Bank, National Association      1 PNC Plaza, 3rd Floor            1 PNC Plaza, 3rd Floor        $62,500,000         $127,500,000
                                       249 Fifth Avenue                  249 Fifth Avenue
                                   Pittsburgh, PA 15222-2707         Pittsburgh, PA 15222-2707
                                          Brian Begg                        Brian Begg
                                       Tel: 412-762-3440                 Tel: 412-762-3440
                                       Fax: 412-705-3231                 Fax: 412-705-3231
------------------------------------------------------------------------------------------------------------------------------------
Credit Agricole Indosuez         600 Travis Street, Suite 2340     600 Travis Street, Suite 2340    $50,000,000              $0
                                       Houston, TX 77002                 Houston, TX 77002
                                         Brian Knezeak                     Brian Knezeak
                                       Tel: 713-223-7001                 Tel: 713-223-7001
                                       Fax: 713-223-7029                 Fax: 713-223-7029
------------------------------------------------------------------------------------------------------------------------------------
Deutsche Bank AG New York             31 West 52nd Street               31 West 52nd Street         $50,000,000              $0
and/or Cayman Islands Branches        New York, NY 10019                New York, NY 10019
                                         Joel Makowsky                     Joel Makowsky
                                       Tel: 212-469-7896                 Tel: 212-469-7896
                                       Fax: 212-469-5711                 Fax: 212-469-5711
------------------------------------------------------------------------------------------------------------------------------------
Allfirst Bank                          25 S Charles St.                  25 S Charles St.           $37,500,000              $0
                                      Baltimore, MD 21201               Baltimore, MD 21201
                                        Stefan Hoenicke                   Stefan Hoenicke
                                       Tel: 410-244-4208                 Tel: 410-244-4208
                                       Fax: 410-244-4239                 Fax: 410-244-4239
------------------------------------------------------------------------------------------------------------------------------------
Arab Bank, PLC                    520 Madison Ave., 2nd Floor       520 Madison Ave., 2nd Floor     $37,500,000              $0
                                      New York, NY 10022                New York, NY 10022
                                        John C.Korthuis                   John C.Korthuis
                                       Tel: 212-715-9741                 Tel: 212-715-9741
                                       Fax: 212-593-4632                 Fax: 212-593-4632
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   17
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
<S>                             <C>                               <C>                               <C>                <C>
Banca Monte dei Paschi di            55 East 59th Street                55 East 59th Street         $37,500,000              $0
Siena S.p.A.                        New York, NY 10022-1112           New York, NY 10022-1112
                                         Serge Sondak                      Serge Sondak
                                       Tel: 212-891-3600                 Tel: 212-891-3600
                                       Fax: 212-891-6144                 Fax: 212-891-6144
------------------------------------------------------------------------------------------------------------------------------------
Bank of Montreal                     US Corporate Banking              US Corporate Banking         $37,500,000              $0
                                        430 Park Avenue                   430 Park Avenue
                                      New York, NY 10022                New York, NY 10022
                                      Bernard J. Silgardo               Bernard J. Silgardo
                                       Tel: 212-605-1647                 Tel: 212-605-1647
                                       Fax: 212-605-1451                 Fax: 212-605-1451
------------------------------------------------------------------------------------------------------------------------------------
National City Bank                   155 East Broad Street             155 East Broad Street        $37,500,000              $0
                                    Columbus, OH 43251-0033           Columbus, OH 43251-0033
                                        William Whitley                   William Whitley
                                       Tel: 614-463-8543                 Tel: 614-463-8543
                                       Fax: 614-463-6770                 Fax: 614-463-6770
------------------------------------------------------------------------------------------------------------------------------------
SunTrust Bank                    1445 New York Ave, NW 5th Fl.     1445 New York Ave, NW 5th Fl.    $37,500,000              $0
                                  Washington, D.C. 20005-2106       Washington, D.C. 20005-2106
                                         Nancy Petrash                     Nancy Petrash
                                       Tel: 202-879-6432                 Tel: 202-879-6432
                                       Fax: 202-879-6137                 Fax: 202-879-6137
------------------------------------------------------------------------------------------------------------------------------------
Bank of Tokyo-Mitsubishi Trust    1251 Avenue of the Americas       1251 Avenue of the Americas     $28,000,000              $0
Company                             New York, NY 10020-1104           New York, NY 10020-1104
                                        William Rhodes                    William Rhodes
                                       Tel: 212-782-4580                 Tel: 212-782-4580
                                       Fax: 212-782-4979                 Fax: 212-782-4979
------------------------------------------------------------------------------------------------------------------------------------
Union Bank of California             445 S. Figueroa St.,              445 S. Figueroa St.,         $22,000,000              $0
                                          Suite 1500                        Suite 1500
                                     Los Angeles, CA 90071             Los Angeles, CA 90071
                                      David Musicant, VP                David Musicant, VP
                                       Tel: 213-236-5023                 Tel: 213-236-5023
                                       Fax: 213-236-4096                 Fax: 213-236-4096
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   18
<TABLE>
------------------------------------------------------------------------------------------------------------------------------------
<S>                             <C>                               <C>                               <C>                <C>
Bank of America, N.A.                    MD2-600-06-13                     MD2-600-06-13            $0                       $0
                                6610 Rockledge Drive, 6th Floor   6610 Rockledge Drive, 6th Floor
                                    Bethesda, MD 20817-1876           Bethesda, MD 20817-1876
                                       Lawrence Saunders                 Lawrence Saunders
                                       Tel: 301-571-0704                 Tel: 301-571-0704
                                       Fax: 301-571-0719                 Fax: 301-571-0719
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>   19
                                    EXHIBIT A


<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------------
                                                 Applicable Margin
                           Applicable Margin            For             Applicable Margin       Applicable        Applicable Margin
    Public Debt Rating             for            Eurodollar Rate          for CD Rate          Margin for       for Utilization Fee
        S&P/Moody's        Base Rate Advances         Advances               Advances           Facility Fee            (25%)
------------------------------------------------------------------------------------------------------------------------------------
<S>                        <C>                   <C>                    <C>                     <C>              <C>
Level 1                            0                    .125%                 .255%              .075%                  .250%
  AA-/AA3 or higher
------------------------------------------------------------------------------------------------------------------------------------
Level 2                            0                    .415%                 .540%              .085%                  .250%
  A+/A/A-/A1/A2/A3
------------------------------------------------------------------------------------------------------------------------------------
Level 3                            0                    .525%                 .650%              .100%                  .250%
  BBB+/Baa1
------------------------------------------------------------------------------------------------------------------------------------
Level 4                            0                    .625%                 .750%              .125%                  .250%
  BBB/Baa2
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Level 5                            0                   1.025%                 .850%              .225%                  .250%
  BBB-/Baa3 or lower
------------------------------------------------------------------------------------------------------------------------------------
</TABLE>


                                                            EXHIBIT AA - FORM OF
                                                                      SWING LINE
                                                                 PROMISSORY NOTE

U.S.$_______________       Dated:  -----_________, ____

                  FOR VALUE RECEIVED, the undersigned, Columbia Energy Group, a
Delaware corporation (the "Borrower"), HEREBY PROMISES TO PAY to the order of
_________________________ (the "Lender") for the account of its Applicable
Lending Office on the earlier of the maturity date for any Swing Line Advance or
the Termination Date (each as defined in the Credit Agreement referred to below)
the principal sum of U.S.$[amount of the Lender's Swing Line Commitment in
figures] or, if less, the aggregate principal amount of the Swing Line Advances
made by the Lender to the Borrower pursuant to the Third Amended and Restated
364-Day Credit Agreement dated as of October 11, 2000 among the Borrower, the
Lender and certain other lenders parties thereto, and Citibank, N.A., as Agent
for the Lender and such other lenders (as amended or modified from time to time,
the "Credit Agreement"; the terms defined therein being used herein as therein
defined) outstanding on the earlier of such maturity date or the Termination
Date as the case may be.

                  The Borrower promises to pay interest on the unpaid principal
amount of each Swing Line Advance from the date of such Swing Line Advance until
such principal amount is paid in full, at such interest rates, and payable at
such times, as are specified in the Credit Agreement.

                  Both principal and interest are payable in lawful money of the
United States of America to Citibank, N.A., as Agent, at 2 Penn's Way, Suite
200, New Castle, DE 19720, Attn: Pia Saenganan, in same day funds. Each Swing
Line Advance owing to the Lender by the Borrower pursuant to the Credit
Agreement, and all payments made on account of principal thereof, shall be
recorded by the Lender and, prior to any transfer hereof, endorsed on the grid
attached hereto which is part of this Promissory Note.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

This Promissory Note is one of the Swing Line Notes referred to in, and is
entitled to the benefits of, the Credit Agreement. The Credit Agreement, among
other things, (i) provides for the making of Swing Line Advances by the Lender
to the Borrower from time to time in an aggregate amount not to exceed at any
<PAGE>   20
time outstanding the U.S. dollar amount first above mentioned, the indebtedness
of the Borrower resulting from each such Swing Line Advance being evidenced by
this Promissory Note, and (ii) contains provisions for acceleration of the
maturity hereof upon the happening of certain stated events.

                  The Borrower hereby waives presentment, demand, protest and
notice of any kind except as is expressly set forth in the Credit Agreement. No
failure to exercise, and no delay in exercising, any rights hereunder on the
part of the holder hereof shall operate as a waiver of such rights.

COLUMBIA ENERGY GROUP
By:  ________________________________
Title:
                       ADVANCES AND PAYMENTS OF PRINCIPAL


<TABLE>
<CAPTION>
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                                                                 AMOUNT OF
      DATE             AMOUNT OF           MATURITY           PRINCIPAL PAID          UNPAID PRINCIPAL              NOTATION
                        ADVANCE              DATE               OR PREPAID                 BALANCE                  MADE BY
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<S>                    <C>                 <C>                <C>                     <C>                          <C>
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</TABLE>


<PAGE>   21
<TABLE>
-----------------------------------------------------------------------------------------------------------------------------------
<S>                    <C>                 <C>                <C>                     <C>                          <C>
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</TABLE>