The new rules would require the fleet of new cars and trucks to average 54.5 miles per gallon in 13 years, up from 28.6 mpg at the end of last year.
The regulations will change the cars and trucks in U.S. showrooms, and push automakers to introduce new technology to make vehicles cleaner and more efficient.
President Barack Obama said in a statement that the new fuel standards "represent the single most important step" his administration has taken to reduce U.S. dependence on foreign oil.
Mitt Romney has opposed the standards. His campaign today called them extreme and said they would drive up the price of new cars. Romney's camp says savings at the pump would be wiped out by rising costs of cars.
