SPRINGFIELD -- An experimental power plant planned for Mattoon could cost Illinois taxpayers tens of millions of dollars more than initially believed.

Illinois lawmakers are considering an arrangement that would require the state to purchase all electricity produced at the proposed FutureGen power plant -- a coal-fired facility designed to operate with near-zero emissions.

Supporters say the deal would help FutureGen qualify for upward of $1 billion in federal grants that would help finance its construction.

But, it also could boost the cost of electricity for a state already struggling to pay its bills. Exactly how much of an increase was not clear Wednesday.

The lack of information left some lawmakers baffled.

"I'm amazed at that," said state Sen. Dale Risinger, R-Peoria. "There are a lot of issues the state of Illinois is biting off with this."

The state spends at least $82 million per year to power its office buildings and other state facilities.

Unlike traditional coal-fired plants, the FutureGen facility would pump carbon dioxide emissions into the ground, avoiding the release of pollutants into the atmosphere. For that reason, the cost to build the facility will be higher than a traditional coal-burning power plant.

But, FutureGen CEO Michael Mudd said the facility would operate on a not-for-profit basis and use federal dollars to reduce construction costs, potentially avoiding a hefty price spike for the state.

"I don't think it will be a significant increase," Mudd said.

State Sen. Dale Righter, R-Mattoon, said he was comfortable with FutureGen's estimates and said he is initially supportive of the plan.

Consumer groups and some senators expressed concerned about the effect of the deal on Illinois taxpayers.

"We want to make sure the risks are minimized," said David Kolata, executive director of the Citizens Utility Board.

Legislation laying out the agreement allows FutureGen to charge rates that reflect not only the cost to operate the plant but also prices that also include debt payments.

The legislation is House Bill 4182.