Six automakers paid fines totaling $6.4 million in 2009 because they failed to comply with federal fuel-efficiency standards.
The government says Porsche Cars North America paid $3.7 million in fines for violations dealing with imported passenger cars and light trucks. Maserati Automobiles of America paid a fine of $1.3 million for imported cars.
The National Highway Traffic Safety Administration also collected fines from Mercedes-Benz's U.S. division, Ferrari North America, Chrysler Group LLC and Fiat Group SpA.
Many manufacturers of luxury vehicles consider the fuel efficiency fines as the cost of doing business. The fines were established to ensure that vehicles meet basic gas mileage standards.