Exhibit F


                       [Letterhead of Steven R. Sullivan]


                                November 26, 2003


Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C. 20549

     Re:  Ameren Corporation -
          Application/Declaration on Form U-1 (File No. 70-10133)

Dear Sirs:

     I refer to the Form U-1 Application/Declaration in the above-referenced
proceeding, as amended (the "Application") under the Public Utility Holding
Company Act of 1935, as amended (the "Act"), filed with the Securities and
Exchange Commission (the "Commission") by Ameren Corporation ("Ameren"), a
Missouri corporation, and to the Commission's order dated November 10, 2003
approving the Application (Holding Co. Act Release No. 27758) (the "Order").
Capitalized terms used in this letter without definition have the meanings
ascribed to such terms in the Application.

     In the Application, Ameren requested Commission authorization under the Act
to acquire, directly or indirectly through one or more subsidiary companies, a
membership interest in PowerTree Carbon Company, LLC ("PowerTree"), a Delaware
limited liability company, and, to the extent such approval is necessary, to
transfer all or a portion of such membership interest to any associate company.
In accordance with the terms of the Application and the Order, Ameren, through
its direct wholly-owned non-utility subsidiary, CIPSCO Investment Company
("CIC"), has executed the Operating Agreement and made its initial capital
contribution to PowerTree.

     I have acted as counsel for Ameren in connection with the Application and,
as such counsel, I am familiar with the corporate proceedings taken by Ameren in
connection with the proposed transaction, as described in the Application. I
have examined originals, or copies certified to my satisfaction, of such
corporate records of Ameren, certificates of public officials, certificates of
officers and representatives of Ameren, and other documents as I have deemed it
necessary to examine as a basis for the opinions hereinafter expressed. In such
examination, I have assumed the genuineness of all signatures and the
authenticity of all documents submitted to me as originals and the conformity
with the originals of all documents submitted to me as copies. As to various
questions of fact material to such opinions, I have, when relevant facts were
not independently established, relied upon certificates of officers of Ameren
and other appropriate persons and statements contained in the Application and
the exhibits thereto.





     Subject to the foregoing, I am of the opinion that:

     (a)  all state laws applicable to the proposed transaction have been
          complied with;

     (b)  (i) PowerTree is validly organized and duly existing under the laws of
          Delaware, and (ii) CIC is entitled to all of the rights and privileges
          of a member of PowerTree as set forth in PowerTree's Operating
          Agreement;

     (c)  CIC has legally acquired the membership interest in PowerTree; and

     (d)  the consummation of the proposed transaction has not violated the
          legal rights of the holders of any securities issued by Ameren or any
          associate company thereof.

     I am an attorney licensed to practice in the State of Missouri and have
acted as counsel to Ameren in connection with the proposed transaction. For
purposes of this opinion, with respect to all matters governed by the laws of
Delaware as applicable to PowerTree, I have relied upon an opinion addressed to
Ameren of Morris, James, Hitchens & Williams LLP, Wilmington, Delaware, which
opinion was filed as an exhibit to the Application.

     I hereby give my written consent to the use of this opinion in connection
with the filing of a certificate pursuant to Rule 24 in the above-referenced
proceeding. This opinion is intended solely for the use of the Commission and
may not be relied upon by any other person for any other purpose.


                                         Very truly yours,


                                         /s/ Steven R. Sullivan
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