ST. LOUIS • Ameren Missouri on Friday asked regulators for permission to raise electric rates by $376 million, or 15 percent, to reimburse the utility for infrastructure upgrades, higher fuel costs and other expenses.

If approved, the average residential customer bill would rise about $14 a month based on usage of 1,100 kilowatt-hours, the utility said. Exact amounts will vary.

"Over the last several years, we have made significant investments in our infrastructure that are producing results," Warner Baxter, Ameren Missouri's chief executive, said in a statement. The company said the reliability of its local power grid and emissions of acid-rain sulfur dioxide at its power plants have improved over the past five years.

Almost a third of the increase, $103 million, would go toward higher fuel expenses, such as the cost of shipping coal from Wyoming, the utility said.

Investments in aging infrastructure to meet environmental and renewable energy requirements make up $85 million of the proposal. And costs of implementing energy efficiency programs are $81 million, Ameren said.

The request comes about six months after the Public Service Commission approved a 7 percent, $172 million increase for the St. Louis-based utility.