Exhibit 99.1


[GRAPHIC OMITTED][GRAPHIC OMITTED]                        One Ameren Plaza
                                                          1901 Chouteau Avenue
                                                          St. Louis, MO 63103


 Contact:

 Media                           Analysts                     Investors
 Susan Gallagher                 Bruce Steinke                Investor Services
 (314) 554-2175                  (314) 554-2574               invest@ameren.com
 sgallagher@ameren.com           bsteinke@ameren.com

 FOR IMMEDIATE RELEASE

                    AMEREN ENTERS INTO EXCLUSIVE NEGOTIATIONS
             FOR THE ACQUISITION OF ILLINOIS POWER FROM DYNEGY INC.

     St.  Louis,  Mo.,  Dec.  5,  2003---Ameren  Corporation  (NYSE:  AEE) today
announced that the company is in exclusive  discussions  with Dynegy Inc. (NYSE:
DYN) on the possible acquisition by Ameren of Decatur,  Il.-based Illinois Power
Company.  There  can be no  assurance  that  these  discussions  will lead to an
agreement or that any such agreement would be completed.

     Illinois Power is an electric and natural gas distribution and transmission
utility serving 590,000  electric and 415,000 gas customers in areas  contiguous
to Ameren's existing Illinois utility service territories.  Ameren,  through its
subsidiaries,  AmerenCILCO,  AmerenCIPS and AmerenUE, currently serves more than
970,000  electric  and gas  customers in Illinois  and has  approximately  3,200
employees  in Illinois.  Ameren has a track  record of  providing  high-quality,
reliable electric and natural gas services in Illinois,  and if a transaction is
consummated,  would  commit to bringing  this same level of  performance  to the
customers and communities served by Illinois Power. In addition,  and consistent
with its past acquisitions of AmerenCILCO and AmerenCIPS,  Ameren would maintain
Illinois  Power's  headquarters  in  Decatur,  Ill.,  honor all  existing  labor
agreements and bring long-term value to all stakeholders.  Further, Ameren would
not propose any special legislation to complete this acquisition.

     Any  transaction  between  the  parties  would be subject  to  satisfactory
completion of Ameren's due diligence,  negotiation of final terms and structure,
negotiation  and execution of definitive  agreements,  receipt of approvals from
the boards of directors of both companies and required regulatory approvals,  in
addition to other conditions.

     Ameren  does  not  anticipate  making  any  further  announcements  until a
definitive agreement is reached or the discussions are terminated.

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     With  assets  of $13.5  billion,  Ameren  owns a  diverse  mix of  electric
generating plants strategically located in its Midwest market with a capacity of
more than 14,500  megawatts.  Ameren serves 1.7 million  electric  customers and
500,000  natural gas  customers  in a 49,000  square-mile  area of Missouri  and
Illinois.

Forward-Looking Statements
--------------------------

     Statements made in this release,  which are not based on historical  facts,
are  "forward-looking"  and,  accordingly,  involve risks and uncertainties that
could cause actual results to differ  materially from those discussed.  Although
such "forward-looking"  statements have been made in good faith and are based on
reasonable assumptions,  there is no assurance that the expected results will be
achieved.  These statements include (without limitation) statements as to future
expectations,  beliefs, plans, strategies,  objectives,  events, conditions, and
financial  performance.  In connection with the "safe harbor"  provisions of the
Private Securities  Litigation Reform Act of 1995, the company is providing this
cautionary  statement  to identify  important  factors  that could cause  actual
results to differ materially from those anticipated.  The following factors,  in
addition to those discussed elsewhere in this release and in past and subsequent
securities  filings,  could  cause  actual  results  to differ  materially  from
management expectations as suggested by such "forward-looking" statements:

o    the satisfactory completion of Ameren's due diligence;
o    the parties ability to negotiate final terms and structure and to negotiate
     and execute definitive transaction agreements;
o    the receipt of board of directors and required regulatory approvals; and
o    the satisfaction of other  conditions  precedent to the consummation of any
     such transaction.

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