DETROIT (AP) - General Motors says it will start selling a Chevrolet Impala sedan next summer that runs on both natural gas and gasoline. The company says both fuels are needed because there are few natural gas filling stations in the U.S. GM says the Impala will be the only factory-produced full-size car that runs on both fuels. Natural gas is plentiful in the U.S. and is cheaper than gasoline. AAA says gas costs about $3.35 per gallon. Natural gas fueling station company Clean Energy says compressed natural gas costs $2.94 for the amount equal to a gallon of diesel fuel. GM didn't reveal the new Impala's price. A gas-powered Impala starts around $28,000. CEO Dan Akerson announced the car at a Washington event marking the 40th anniversary of the OPEC oil embargo.