<PAGE>

                                                                     EXHIBIT 3.1

                                                                               D
/s/ [ILLEGIBLE]
--------
Examiner                The Commonwealth of Massachusetts
                             William Francis Galvin
                          Secretary of the Commonwealth
              One Ashburton Place, Boston, Massachusetts 02108-1512

                            ARTICLES OF ORGANIZATION
                           (General Laws, Chapter 164)

CC
--------
Name
Approved

                                    ARTICLE I
                      The exact name of the corporation is:

                              COLONIAL GAS COMPANY


                                   ARTICLE II

         The purpose of the corporation is to engage in the following
         business activities:

         See attached Continuation Sheet 2.

C    |_|
P    |X|
M    |_|
R.A. |_|

9
----
P.C.

Note: If the space provided under any article or item on this form is
insufficient, additions shall be set forth on one side only of separate 8 1/2 x
11 sheets of paper with a left margin of at least 1 inch. Additions to more than
one article may be made on a single sheet so long as each article requiring each
addition is clearly indicated.
<PAGE>

                                   ARTICLE III

State the total number of shares and par value, if any, of each class of stock
which the corporation is authorized to issue.

--------------------------------------------------------------------------------
   WITHOUT PAR VALUE                          WITH PAR VALUE
--------------------------------------------------------------------------------
 TYPE     NUMBER OF SHARES         TYPE      NUMBER OF SHARES    PAR VALUE
--------------------------------------------------------------------------------
Common:                          Common:     200,000             $1.00
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
Preferred:                       Preferred:
--------------------------------------------------------------------------------

--------------------------------------------------------------------------------

                                   ARTICLE IV

If more than one class of stock is authorized, state a distinguishing
designation for each class. Prior to the issuance of any shares of a class, if
shares of another class are outstanding, the corporation must provide a
description of the preferences, voting powers, qualifications, and special or
relative rights or privileges of that class and of each other class of which
shares are outstanding and of each series then established within any class.

N/A


                                    ARTICLE V

The restrictions, if any, imposed by the Articles of Organization upon the
transfer of shares of stock of any class are:

None.

                                   ARTICLE VI

"Other lawful provisions, if any, for the conduct and regulation of the business
and affairs of the corporation, for its voluntary dissolution, or for limiting,
defining, or regulating the powers of the corporation, or of its directors or
stockholders, or of any class of stockholders:

See attached Continuation Sheets 6A, 6B and 6C.

**If there are no provisions state "None".
Note: The preceding six (6) articles are considered to be permanent and may ONLY
be charged by filing appropriate Articles of Amendment.
<PAGE>

                              CONTINUATION SHEET 2

      To engage in business as a gas utility company in any city or town of the
Commonwealth of Massachusetts; to exercise any and all rights, powers, licenses,
permits, privileges, authorizations and franchises at any time possessed by the
corporation or by any predecessor or constituent corporation; to engage in any
activity in any way connected with, incident to or in furtherance of the
foregoing activities; to engage in any other activity lawful for a corporation
subject to Chapter 164 of the Massachusetts General Laws; to engage in any
business, operation or activity through a wholly or partly owned subsidiary; and
to engage in any business, operation or activity referred to above to the same
extent as might an individual, whether as principal, agent, contractor or
otherwise, and either alone or in conjunction or a joint venture or other
arrangement with any corporation, association, trust, firm or individual.
<PAGE>

                              CONTINUATION SHEET 6A

                                     BY-LAWS

The directors may make, amend or repeal the by-laws in whole or in part, except
with respect to any provision thereof which by law or the by-laws requires
action by the stockholders.

                              STOCKHOLDERS MEETINGS

Meetings of the stockholders may be held anywhere in the United States.

                      RELIANCE UPON BOOKS OF ACCOUNT, ETC.

Each director and officer of the corporation shall, in the performance of his
duties, be fully protected in relying in good faith upon the books of account of
the corporation, reports made to the corporation by any of its officers or
employees or by counsel, accountants, appraisers or other experts or consultants
selected with reasonable care by the directors, or upon other records of the
corporation.

                              CERTAIN TRANSACTIONS

The directors shall have the power to fix from time to time their compensation.
No person shall be disqualified from holding any office by reason of any
interest. In the absence of fraud, any director, officer or stockholder of this
corporation individually, or any individual having any interest in any concern
which is a stockholder of this corporation, or any concern in which any such
directors, officers, stockholders or individuals have any interest, may be a
party to, or may be pecuniarily or otherwise interested in, any contract,
transaction or other act of this corporation, and

      (1)   such contract, transactions or act shall not be in any way
            invalidated or otherwise affected by that fact;

      (2)   no such director, officer, stockholder or individual shall be liable
            to account to this corporation for any profit or benefit realized
            through any such contract, transaction or act; and

      (3)   any such director of this corporation may be counted in determining
            the existence of a quorum at any meeting of the directors or of any
            committee thereof which shall authorize any such contract,
            transaction or act, and may vote to authorize the same;
<PAGE>

                              CONTINUATION SHEET 6B

provided, however, that any contract, transaction or act in which any director
or officer of this corporation is so interested individually or as a director,
officer, trustee or member of any concern which is not a subsidiary or affiliate
of this corporation, or in which any directors or officers are so interested as
holders, collectively, of a majority of shares of capital stock or other
beneficial interest at the time outstanding in any concern which is not a
subsidiary or affiliate of this corporation, shall be duly authorized or
ratified by a majority of the directors who are not so interested and to whom
the nature of such interest has been disclosed;

      the term "interest" including personal interest and interest as a
      director, officer, stockholder, shareholder, trustee, member or
      beneficiary of any concern;

      the term "concern" meaning any corporation, association, trust,
      partnership, firm, person or other entity other than this corporation; and

      the phrase "subsidiary or affiliate" meaning a concern in which a majority
      of the directors, trustees, partners or controlling persons are elected or
      appointed by the directors of this corporation, or are constituted of the
      directors or officers of this corporation.

To the extent permitted by law, the authorizing or ratifying vote of a majority
in interest of each class of the capital stock of this corporation outstanding
and entitled to vote for directors at any annual meeting or a special meeting
duly called for the purpose (whether such vote is passed before or after
judgment rendered in a suit with respect to such contract, transaction or act)
shall validate any contract, transaction or act of this corporation, or of the
board of directors or any committee thereof, with regard to all stockholders of
this corporation, whether or not of record at the time of such vote, and with
regard to all creditors and other claimants under this corporation;

      provided, however, that with respect to the authorization or ratification
      of contracts, transactions or acts in which any of the directors, officers
      or stockholders of this corporation have an interest, the nature of such
      contracts, transactions or acts and the interest of any director, officer
      or stockholder therein shall be summarized in the notice of any such
      annual or special meeting, or in a statement or letter accompanying such
      notice, and shall be fully disclosed at any such meeting;

      provided, also, that stockholders so interested may vote at any such
      meeting; and
<PAGE>

                              CONTINUATION SHEET 6C

provided, further, that any failure of the stockholders to authorize or ratify
such contract, transaction or act not be deemed in any way to invalidate the
same or to deprive this corporation, its directors, officers or employees of its
or their right to proceed with such contract, transaction or act.

No contract, transaction or act shall be avoided by reason of any provision of
this paragraph which would be valid but for those provisions.

                                   PARTNERSHIP

The corporation may be a partner in any business enterprise which the
corporation would have power to conduct by itself.
<PAGE>

                             CONTINUTATION SHEET 8b

                           CG ACQUISITION GAS COMPANY

                               Officers & Director


            Name                   Resident Address          Post Office Address
            ----                   ----------------          -------------------

President   Walter J. Flaherty     76 Old Post Road          Eastern Enterprises
                                   East Walpole, MA 02032    9 Riverside Road
                                                             Weston, MA 02493

Treasurer   Jean A. Scholtens      2 Rice Spring Lane        Eastern Enterprises
                                   Wayland, MA 01778         9 Riverside Road
                                                             Weston, MA 02493

Clerk       L. William Law, Jr.    75 Bacon Street           Eastern Enterprises
                                   Winchester, MA 01890      9 Riverside Road
                                                             Weston, MA 02493

Assistant   W. Brett Davis         6 Wellington Street       Eastern Enterprises
Clerk                              Boston, MA 02118          9 Riverside Road
                                                             Weston, MA 02493

Director    Walter J. Flaherty     76 Old Post Road          Eastern Enterprises
                                   East Walpole, MA 02032    9 Riverside Road
                                                             Weston, MA 02493
<PAGE>

                                   ARTICLE VII

The effective date of organization of the corporation shall be the date approved
and filed by the Secretary of the Commonwealth. If a later effective date is
desired, specify such date which shall not be more than thirty days after the
date of filing.

      N/A

                                  ARTICLE VIII

The information contained in Article VIII is not a permanent part of the
Articles of Organization.

a. The street address (post office boxes are not acceptable) of the principal
   office of the corporation in Massachusetts is:

   c/o Boston Gas Company, One Beacon Street, Boston, MA 02108

b. The name, residential address and post office address of each director and
   officer of the corporation is as follows:

              NAME        RESIDENTIAL ADDRESS        POST OFFICE ADDRESS

President:

Treasurer:

Clerk:                See attached Continuation Sheet 8b.

Directors:


c. The fiscal year (i.e., tax year) of the corporation shall end on the last day
   of the month of: December

d. The name and business address of the resident agent, if any, of the
   corporation is: N/A

e. The date fixed by the by-laws for the annual meeting of Stockholders is:
   2nd Thursday in March unless otherwise determined by the Board of Directors.

                                   ARTICLE IX

By-laws of the corporation have been duly adopted and the president, treasurer,
clerk and directors whose names are set forth above, have been duly elected.

IN WITNESS WHEREOF AND UNDER THE PAINS AND PENALTIES OF PERJURY, I/we, whose
signature(s) appear below as incorporator(s) and whose name(s) and business or
residential address(es) are clearly typed or printed beneath each signature do
hereby associate with the intention of forming this corporation under the
provisions of General Laws, Chapter 164 and do hereby sign these Articles of
Organization as incorporator(s) this 5th day of August, 1999.

/s/ L. William Law, Jr., Esq.
--------------------------------------------------------------------------------
L. William Law, Jr., Esq.
--------------------------------------------------------------------------------
c/o Eastern Enterprises
--------------------------------------------------------------------------------
9 Riverside Road
--------------------------------------------------------------------------------
Weston, MA 02493
--------------------------------------------------------------------------------

Note: If an existing corporation is acting as incorporator, type in the exact
name of the corporation, the state or other jurisdiction where it was
incorporated, the name of the person signing on behalf of said corporation and
the title he/she holds or other authority by which such action is taken.
<PAGE>

                        THE COMMONWEALTH OF MASSACHUSETTS

                            ARTICLES OF ORGANIZATION
                           (General Laws, Chapter 164)

            ========================================================

            I hereby certify that, upon examination of these
            Articles of Organization, duly submitted to me, it
            appears that the provisions of the General Laws relative
            to the organization of corporations have been complied
            with, and I hereby approve said articles; and the filing
            fee in the amount of $200 having been paid, said
            articles are deemed to have been filed with me this 6th
            day of August 1999.

            Effective date: ________________________________________

                           /s/ William Francis Galvin

                             WILLIAM FRANCIS GALVIN

                          Secretary of the Commonwealth

            FILING FEE: One tenth of one percent of the total
            authorized capital stock, but not less than $200.00. For
            the purpose of filing, shares of stock with a par value
            less than $1.00, or no par stock, shall be deemed to
            have a par value of $1.00 per share.

                         TO BE FILLED IN BY CORPORATION

                      Photocopy of document to be sent to:

                             W. Brett Davis, Esq.
                  -------------------------------------------
                             c/o Eastern Enterprises
                  -------------------------------------------
                             9 Riverside Road
                  -------------------------------------------
                             Weston, MA 02493
                  -------------------------------------------
                  Telephone: (781) 647-2300
                             --------------------------------