Document:

<PAGE>

                                                                  Exhibit 10.6.4

                               EASTERN ENTERPRISES

                          Amendment of Trust Agreement

      Instrument of amendment dated September 22, 1999 by and between Eastern
Enterprises ("Eastern") and Key Trust Company of Ohio, N.A. (the "Trustee"):

      WHEREAS Eastern and the Trustee are parties to a trust agreement
originally dated January 29, 1987 and subsequently amended, including to
substitute the current Trustee as trustee of the trust established under such
agreement (as heretofore amended, the "Trust Agreement"); and

      WHEREAS Eastern wishes to amend the Trust Agreement as hereinafter
provided; and

      WHEREAS Eastern has reserved the right to make such amendment under
Section 10(a) of the Trust Agreement;

      NOW, THEREFORE, in consideration of these premises, the Trust Agreement is
hereby amended as follows, effective immediately:

      1. Section 2(a) of the Trust Agreement is amended by deleting that portion
of the last sentence thereof which begins "and further provided, that no such
modification or supplement . . ." and ends ". . . prior to the Change of
Control" and replacing the deleted text with the following:

      "and further provided, that no such modification or supplement upon or
      following a Change of Control shall (i) expand the list of plans or other
      compensation or benefit arrangements (as set forth in the most recent
      Schedule A delivered to the Trustee prior to the Change of Control) under
      which compensation or benefits may be provided from assets of the Trust,
      nor shall any amendment or modification of any such plan or arrangement
      adopted upon or following the Change of Control be taken into account in
      determining compensation or benefits that may be provided from assets of
      the Trust (but nothing in this proviso shall be construed as limiting the
      right of a Trust Beneficiary to claim benefits from Eastern or its
      subsidiaries, or a successor, in respect of any such amendment or
      modification), or (ii) add any person as a Trust Beneficiary who was not
      an employee or trustee of Eastern prior to the Change of Control."

      IN WITNESS WHEREOF, Eastern Enterprises and the Trustee have caused this
instrument of amendment to be executed by their duly authorized officers as of
the date set forth above.

                                    EASTERN ENTERPRISES

                               By:  /s/ J. Atwood Ives
                                    -----------------------------

                                    KEY TRUST COMPANY OF OHIO, N.A.

                               By:  /s/ Margaret Halloran, AVP
                                    -----------------------------

----------
Approved by the Board of Trustees on September 22, 1999<PAGE>

                                                                 Exhibit 10.19.3

                                 AMENDMENT NO. 3
                               TO CREDIT AGREEMENT
                            AND OTHER LOAN DOCUMENTS

      AMENDMENT NO. 3 DATED AS OF AUGUST 20, 1999 ("AMENDMENT NO. 3") TO THE
CREDIT AGREEMENT dated as of December 31, 1994 (as amended and in effect
immediately prior to the date hereof, the "Credit Agreement"), by and among (a)
EASTERN ENTERPRISES, a Massachusetts voluntary association, BOSTON GAS COMPANY,
a Massachusetts corporation, MIDLAND ENTERPRISES INC., a Delaware corporation
(collectively the "Borrowers"), (b) FIFTH THIRD BANK, MELLON BANK, N.A., MORGAN
GUARANTY TRUST COMPANY OF NEW YORK, FLEET NATIONAL BANK, THE BANK OF NOVA
SCOTIA, AND BANKBOSTON, N.A. (F/K/A THE FIRST NATIONAL BANK OF BOSTON)
(collectively, the "Banks"), and (c) BANKBOSTON, N.A. (F/K/A THE FIRST NATIONAL
BANK OF BOSTON), as agent (in such capacity, the "Agent") for the Banks, AND
OTHER LOAN DOCUMENTS.

      WHEREAS, the Borrowers, the Agent and the Banks have agreed to modify
certain terms and conditions of the Credit Agreement and the other Loan
Documents, as more fully set forth herein; and

      NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Borrowers, the Agent and the
Banks hereby agree as follows:

      (Sec.) 1. DEFINITIONS. Capitalized terms used herein and not otherwise
defined herein have the meanings given to such terms in the Credit Agreement, as
amended hereby.

      (Sec.) 2. AMENDMENT TO SECTION 1 OF THE CREDIT AGREEMENT. Section 1.1 of
the Credit Agreement is hereby amended as follows:

            (a) The definition of "Designated Documents" set forth in such
      section is amended and restated in its entirety to read as follows:

      "Designated Documents": Eastern's, Boston Gas' and Midland's 1998 Form
      10-K's and Eastern's, Boston Gas' and Midland's quarterly reports on Form
      10-Q's for the fiscal quarters of such Borrowers ended March 31, 1999 and
      June 30, 1999.

            (b) The definition of "FNBB" set forth in such section is amended
      and restated in its entirety to read as follows:

      "FNBB":  BankBoston,  N.A. (f/k/a The First National Bank of Boston),  a
      national banking association.

            (c) The definition of "Special Counsel" set forth in such section is
      amended and restated in its entirety to read as follows:

      "Special  Counsel":  Bingham  Dana LLP,  or such other firm  selected by
      the Agent.

      (Sec.) 3. AMENDMENT TO SECTION 4 OF THE CREDIT AGREEMENT. Section 4 of the
Credit Agreement is hereby amended by inserting a new subsection 4.18 to read as
follows:

            4.18 YEAR 2000 PROBLEM. Each of the Borrowers have (i) reviewed the
      areas within their businesses and operations which could be adversely
      affected by failure to become "Year 2000 Compliant" (i.e. that computer
      applications, imbedded microchips and other systems used by any Borrower
      will be able properly to recognize and perform properly date-sensitive
      functions involving certain dates prior to and any date after December 31,
      1999), (ii) developed a detailed plan and timetable to become Year 2000
      Compliant in a timely manner, and (iii) committed adequate resources to
      support the Year 2000 plan of the Borrowers. Based upon such review, each
      of the Borrowers reasonably believes that the Borrowers will become "Year
      2000 Compliant" in a timely manner except to the extent that failure to do
      so will not have any materially adverse effect on the business or
      financial condition of any Borrower.

      (Sec.) 4. AMENDMENT TO SECTION 5 OF THE CREDIT AGREEMENT. Section 5.5 of
the Credit Agreement is hereby amended by deleting the words "the good standing
and legal existence of, and the payment of franchise taxes therein by, such
Borrower" and substituting in place thereof the words "the good standing and
legal existence of, and the payment of franchise taxes therein by, such Borrower
(except that with respect to Eastern, such certificate shall certify as to
Eastern's filing of all necessary certificates, its payment of all necessary
fees and its ability to exercise in Massachusetts all of the powers recited in
its Declaration of Trust and to transact business in Massachusetts)".

      (Sec.) 5. AMENDMENT TO SECTION 6 OF THE CREDIT AGREEMENT. Section 6.1 of
the Credit Agreement is hereby amended and restated in its entirety to read as
follows:

            6.1 COMPLIANCE. On each Borrowing Date, and after giving effect to
      the Loans to be made on such date (a) each of the Borrowers and the
      Guarantor shall be in compliance with all of the terms, covenants and
      conditions of this Agreement and the other Loan Documents applicable to
      it, (b) there shall exist no Event of Default, and (c) the representations
      and warranties contained in this Agreement or in any other Loan Document,
      or otherwise in writing made by any Borrower or the Guarantor in
      connection herewith or therewith shall be true and correct in all material
      respects with the same effect as though such representations and
      warranties had been made on such Borrowing Date (except such thereof as
      specifically refer to an earlier date and except for changes resulting
      from mergers, consolidations or Sales of assets or stock not prohibited by
      paragraphs 8.6, 8.6A or 8.6B and changes occurring in the ordinary course
      of business that singly or in the aggregate are not materially adverse)
      and the Agent shall have received a certificate, dated the Borrowing Date,
      and signed by a duly authorized officer of Eastern, to the same effect as
      all of the foregoing matters.

      (Sec.) 6. SUBSTITUTION OF NEW EXHIBIT H TO THE CREDIT AGREEMENT. The
Credit Agreement is hereby amended by deleting Exhibit H thereto in its entirety
and substituting in place thereof the form of Exhibit H attached hereto.

      (Sec.) 7. REFERENCES TO THE FIRST NATIONAL BANK OF BOSTON OR FNBB. Each
reference in the Credit Agreement and the other Loan Documents to The First
National Bank of Boston or FNBB shall be deemed to be a reference to BankBoston,
N.A.

      (Sec.) 8. CONDITIONS TO EFFECTIVENESS. This Amendment No. 3 shall be
effective as of the date hereof upon the satisfaction of each of the following
conditions:

      (a)   The  Amendment.  This  Amendment  No. 3 shall  have  been duly and
properly  authorized,  executed and  delivered to the Agent by the  Borrowers,
the Agent and the Banks, and shall be in full force and effect.

      (b) Representations and Warranties; Absence of Default. Each of the
representations and warranties made by or on behalf of the Borrowers to the
Banks or the Agent in the Credit Agreement, as amended hereby, and the other
Loan Documents shall be true and correct in all material respects when made,
shall be repeated on and as of the date hereof, and shall be true and correct in
all material respects on and as of such date except, in each case, as affected
by the consummation of the transactions contemplated hereby or by the Loan
Documents and to the extent that such representation or warranty may relate by
its terms solely to a prior date, and no Default or Event of Default shall have
occurred and be continuing on the date hereof.

      (Sec.) 9. RATIFICATION, ETC. Except as otherwise expressly set forth
herein, all terms and conditions of the Credit Agreement and the other Loan
Documents are hereby ratified and confirmed and shall remain in full force and
effect. Without limiting the generality of the foregoing, each of the Borrowers
expressly affirms all of its obligations under each of the Loan Documents to
which it is a party, including, without limitation, the Credit Agreement, as
amended hereby. Nothing herein shall be construed to be an amendment or a waiver
of any requirements of the Credit Agreement or of any of the other Loan
Documents except as expressly set forth herein.

      (Sec.) 10. COUNTERPARTS. This Amendment No. 3 may be executed in any
number of counterparts, which together shall constitute one instrument.

      (Sec.) 11. GOVERNING LAW. THIS AMENDMENT NO. 3 SHALL BE A CONTRACT UNDER
THE LAWS OF THE COMMONWEALTH OF MASSACHUSETTS, SHALL FOR ALL PURPOSES BE
CONSTRUED IN ACCORDANCE WITH AND GOVERNED BY THE INTERNAL LAWS OF SAID
COMMONWEALTH, WITHOUT REFERENCE TO CONFLICTS OF LAW, AND IS INTENDED TO TAKE
EFFECT AS A SEALED INSTRUMENT.

      (Sec.) 12. IMMUNITY OF INDIVIDUALS. Reference is hereby made to the
Declaration of Trust establishing Eastern Enterprises, dated July 18, 1929, a
copy of which has been filed with the Secretary of the Commonwealth of
Massachusetts and elsewhere as required by law, and to any and all amendments
thereto so filed or hereafter filed. The name "Eastern Enterprises" refers to
the trustees under said Declaration of Trust, as trustees and not personally,
and no trustee, shareholder, officer or agent of Eastern shall be held to any
personal liability hereunder or in connection with the affairs of Eastern, but
only the trust estate under said Declaration of Trust is liable under this
Agreement, any Guaranty, the Notes or any other Loan Document.

                 [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
<PAGE>

      IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 3
as an instrument under seal to be effective as of the date first above written.

                               EASTERN ENTERPRISES

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

                               BOSTON GAS COMPANY

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

                               MIDLAND ENTERPRISES INC.

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

                               BANKBOSTON, N.A.
                               (f/k/a  The  First  National  Bank of  Boston),
                               Individually and as Agent

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

                               THE BANK OF NOVA SCOTIA

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

                               FIFTH THIRD BANK

                               By:
                               ---------------------------
                               Title:
<PAGE>

                                MELLON BANK, N.A.

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

                               MORGAN GUARANTY TRUST
                               COMPANY OF NEW YORK

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

                               FLEET NATIONAL BANK

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

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