Ameren Corp.'s (AEE) Illinois utilities on Friday filed a request with state regulators for a $226 million electric and gas rate increase.

The rate increase, which wouldn't take effect before May 2010, would cover costs associated with upgrades to the electric grid and to natural gas infrastructure.

"We understand today's economic challenges are affecting the people, businesses and industries we serve as well as our own organization," said Scott Cisel, Ameren Illinois' president and chief executive, in a prepared statement. "We recognize that any rate increase will be cause for concern. However, be assured that our proposed rate increases are necessary to provide the essential financial resources to meet our obligations to our customers."

The electric rate increases will provide Ameren with an 11.75%-12.25% return on equity, while the rise in natural gas rates will give the utilities an 11.25%-11.6% return. The average Ameren Illinois residential electric customer will pay $59-$97 more a year, while the average residential natural gas customer will pay $38-$60 more.

-By Christine Buurma, Dow Jones Newswires; 201-938-2061; christine.buurma@dowjones.com