CERTIFICATE OF INCORPORATION
                                       OF
                       PLUM STREET ENERGY MARKETING, INC.


      THE UNDERSIGNED, acting as the incorporator of a corporation under and in
accordance with the General Corporation Law of the State of Delaware, hereby
adopts the following Certificate of Incorporation for such corporation:

      FIRST:      The name of the corporation (hereinafter referred to as the
                  "Corporation") is Plum Street Energy Marketing, Inc.

      SECOND:     The street address of the initial registered office of the
                  Corporation in the State of Delaware is The Corporation Trust
                  Company, 1209 Orange Street, City of Wilmington, County of New
                  Castle, Delaware 19801. The name of the initial registered
                  agent of the Corporation in the State of Delaware at such
                  address is The Corporation Trust Company.

      THIRD:      The purpose for which the Corporation is organized is the
                  transaction of any or all lawful acts and activities for which
                  corporations may be incorporated under the General Corporation
                  Law of the State of Delaware.

      FOURTH:     The total number of shares of capital stock which the
                  Corporation shall have the authority to issue is 10,000, of a
                  par value of $1.00 a share and having an aggregate par value
                  of $10,000. All of such shares shall be common stock of the
                  Corporation ("Common Stock"). Except as otherwise provided by
                  law, the shares of stock of the Corporation may be issued by
                  the Corporation from time to time in such amounts, for such
                  consideration and for such corporate purposes as the Board of
                  Directors of the Corporation may from time to time determine.
                  Subject to the provisions of applicable law or the By-laws of
                  the Corporation with respect to the closing of the transfer
                  books or the fixing of a record date for the determination of
                  stockholders entitled to vote, each holder of record of shares
                  of Common Stock shall be entitled to one vote for each share
                  of Common Stock standing in his name on the books of the
                  Corporation in any stockholder vote in which any of such
                  holders is entitled to participate.

      FIFTH:      The name and address of the incorporator is as follows:

                  Name                    Address
                  ----                    -------

                  Martin C. Ernst         3000 K. Street, NW
                                          Suite 300
                                          Washington, DC 20007-5116

      SIXTH:      The Incorporator shall adopt the initial By-laws and serve as
                  the sole director until the first meeting of stockholders at
                  which time successors directors shall


                  be duly elected and qualified. Thereafter, the By-laws of the
                  Corporation may be amended or repealed by a majority of the
                  Board of Directors of the Corporation. Any By-laws adopted by
                  the Board of Directors may be amended or repealed by the
                  stockholders entitled to vote thereon.

      SEVENTH:    No director shall be personally liable to the Corporation or
                  any stockholder for monetary damages for breach of fiduciary
                  duty as a director, expect for liability (1) for breach of a
                  director's duty of loyalty to the corporation or its
                  stockholders; (2) for acts or omissions not in good faith or
                  which involve intentional misconduct or a knowing violation of
                  law; (3) under Section 174 of the General Corporation law of
                  the State of Delaware; or (4) for any transaction from which
                  the director derived an improper personal benefit. Neither the
                  amendment or repeal of this Article SEVENTH, nor the adoption
                  of any provision of the Certificate of Incorporation
                  inconsistent with the Article, shall eliminate or reduce the
                  effect of this Article in respect to any matter occurring, or
                  any cause of action, suit or claim that, but for this Article,
                  would accrue or arise, prior to such amendment, repeal or
                  adoption of an inconsistent provision.

      EIGHTH:     The Corporation shall have the power to indemnify persons
                  against expenses (including attorney's fees), judgments, fines
                  and amounts paid in settlements arising from any threatened,
                  pending or completed action, suit or proceeding, as provided
                  by the General Corporation Law of the State of Delaware and as
                  may otherwise be permitted by law. The Board of Directors may
                  authorize the Corporation to purchase and maintain insurance
                  on behalf of any person who is or who was a director, officer,
                  employee, agent or shareholder of the Corporation, or is or
                  was serving at the request of the Corporation as a director,
                  officer, employee, agent of another corporation, partnership,
                  joint venture, trust or other enterprise, against any
                  liability asserted against such person and incurred by such
                  person in any such capacity or arising out of his or her
                  status as such, but such insurance shall cover a shareholder
                  only to the extent such shareholder is acting on behalf of the
                  corporation.

      NINTH:      Election of Directors need not be by written ballot. Any
                  director or the entire Board of Directors may be removed, with
                  or without cause, by the holders of a majority of the shares
                  then entitled to vote at an election of directors, except as
                  otherwise provided by law.

      IN WITNESS WHEREOF, the Incorporator has signed and executed this
Certificate Incorporation on this, the 13th day of February, 1996, and
acknowledges the same to be my act.

                                                             INCORPORATOR:


                                                             /s/ Martin C. Ernst
                                                             Martin C. Ernst