CHICAGO - The Illinois Commerce Commission approved a $69 million rate increase Wednesday for Nicor Inc. that officials said will add up to $3 to the average residential customer's monthly bill.

The approval means the average customer will see an approximately $2.50 increase on their bill starting in April, said Nicor spokeswoman Annette Martinez.

Some of Nicor's more than 2 million northern Illinois customers could see up to a $3 monthly increase, depending on usage and the season, ICC spokeswoman Beth Bosch said.

The approved rate hike was about half the original $140 million the company requested last year. That would have pushed residential customers' gas rates up 5 percent, or about $4.86 a month.

ICC officials said they reduced Nicor's 2008 request in areas including incentive compensation expense. In a statement, commission officials said Nicor "proved its case to collect a $69 million increase."

Nicor's original request was criticized by many, including Illinois Attorney General Lisa Madigan and the Citizens Utility Board, which planned to appeal Wednesday's decision.

CUB Executive Director David Kolata claimed the increase illustrated how "the needs of consumers are being overshadowed by corporate interests."

"It's difficult, if not impossible, to stimulate a struggling economy if consumers are dumping more and more of their hard-earned cash into their natural gas bills," Kolata said. "As lawmakers struggle to put more money back into consumers' pockets, today's decision just takes more out."

Madigan expressed a similar sentiment Wednesday.

"I am disappointed in the size of the Nicor rate hike approved today by the Illinois Commerce Commission especially during these challenging economic times," Madigan said. "Such a large increase puts the interests of utilities ahead of consumers at a time when Illinois families can least afford it."

She said her office will review the commission's ruling and consider legal options available for Illinois consumers.

Nicor has defended its request, saying the company has sought rate increases only three times in 20 years.

"We kept our rate relief request to the minimum needed to maintain safe and reliable natural gas service to our more than 2 million customers," Martinez said.

She added that the company has among the lowest rates in Illinois and is competitive nationwide.

The increase does not apply to the cost of gas itself. It pays for the cost of delivering gas, which equals up to 20 percent of a customer's bill, Nicor officials said.