The U.S. Environmental Protection Agency has ordered Hyundai and Kia Motors to correct the official fuel economy estimates on their cars, saying they were overstated for 2011 and 2013 models.

Thirteen models are subject for correction including the Elantra, Azera, Genesis and Soul.

The actual average gas mileage on the cars was eleven-point-five kilometers per liter to eleven-point-one kilometers per liter, around three percent less than the official stated mileage.

The motor companies said there had been an error in the calculations and offered a formal apology as well as compensation methods.

Compensation for the cars is expected to reach 80 billion won, as the two motor companies sold 900-thousand units over the last three years.