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Ameren Joins Midwest Independent Transmission System Operator (Midwest ISO) Through GridAmerica
Ameren Corporation (NYSE: AEE) today announced that two of its operating subsidiaries, AmerenUE and AmerenCIPS, on Saturday transferred functional control of their transmission systems to the Midwest Independent Transmission System Operator Inc. (Midwest ISO).

This action moves operation of more than 5,000 circuit miles of high-voltage power lines into a Regional Transmission Organization (RTO) and complies with requirements imposed on AmerenUE and AmerenCIPS by the Federal Energy Regulatory Commission (FERC) to participate in an RTO.

Concurrent with the transfer that took place on Saturday, Ameren also began taking regional transmission services from the Midwest ISO to serve its retail load.

"Ameren customers should see no real change in the reliable service they have always received," said Ameren Senior Vice President, Energy Delivery David Whiteley. "Our company has been singularly focused on process and quality issues to ensure the smooth transition to the Midwest ISO."

The not-for-profit Midwest ISO is one of several RTOs authorized in recent years under FERC policy. Ameren is participating in the Midwest ISO through a contractual agreement with GridAmerica LLC, a for-profit independent transmission company.

"We have a strong working relationship with both the Midwest ISO and with GridAmerica," Whiteley added. "We look forward to a long and productive relationship with these companies."

GridAmerica is made up of AmerenUE and AmerenCIPS; American Transmission Systems, Inc., a transmission subsidiary of FirstEnergy Corp.; and Northern Indiana Public Service Company, a subsidiary of NiSource, Incorporated. AmerenCILCO, another Ameren subsidiary, was already a transmission-owning member of the Midwest ISO.

GridAmerica, the nation's first multi-system independent transmission company, is based in Cleveland, Ohio, and managed by a subsidiary of National Grid USA. With Ameren, GridAmerica's transmission system now includes 28,000 megawatts of generation capacity, 27,000 megawatts of load, and 14,000 miles of transmission lines across 46,000 square miles of service territory in five states.

The Midwest ISO is responsible for evaluating and coordinating requests for access to the regional power grid on a non-discriminatory basis under the terms of the Midwest ISO tariff. The Midwest ISO schedules transactions across the organization's entire "footprint," which includes more than 96,000 miles of transmission lines spanning 600,000 square miles over portions of 15 states and one Canadian province. GridAmerica is the scheduling agent for that part of the Midwest ISO that resides in the GridAmerica area, which now includes Ameren. As a result of Ameren's participation in the Midwest ISO, Ameren has received $26 million for the refund of an exit fee that Ameren paid to the Midwest ISO in 2001 and reimbursement of funds Ameren invested in the proposed Alliance RTO. This refund will benefit earnings by approximately 7 cents per share in the second quarter of 2004 and was included in Ameren's previous earnings guidance for 2004.

With assets of $14.6 billion, Ameren owns a diverse mix of electric generating plants strategically located in its Midwest market with a capacity of more than 14,600 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.