INDIANAPOLIS | The Indiana Supreme Court dealt NIPSCO a loss Tuesday in a billing dispute with U.S. Steel.

In 1999, the parties agreed to a long-term contract establishing prices the utility would charge U.S. Steel to supply electricity to the steelmaker's Gary Works plant. One price schedule applied to a fixed number of kilowatt hours per month, and another established the cost of overages.

In 2005, the fixed prices in the contract expired, and U.S. Steel began paying market-based prices. But the steelmaker argued its agreement with NIPSCO applied the higher market-based prices only to its fixed monthly consumption, not overages.

The Indiana Utility Regulatory Commission agreed with U.S. Steel in 2006. But the Indiana Court of Appeals reversed that decision in 2007 and ordered the regulatory commission to calculate how much U.S. Steel owed NIPSCO.

The state Supreme Court on Tuesday reversed the appellate ruling. But it's not clear how much the decision could cost NIPSCO.

"We are in the process of reviewing today's decision, and we need time to evaluate and review the impacts of the court's ruling to determine what the appropriate next steps are, if any," NIPSCO spokesman Nick Meyer said Tuesday.

U.S. Steel spokeswoman Erin DiPietro said the company is pleased with the ruling. She declined further comment.