Two car manufacturers could face sanctions from the U.S. government for overstating the gas mileage on most of their models, and some car owners could get refunds for the difference in fuel economy.

During an audit, the Environmental Protection Agency found Hyundai and Kia overstated their gas mileage by one to six miles per gallon, depending on the model.

Now, the automakers have to retrofit window stickers on cars, reducing their fuel economy figures.

Hyundai and Kia executives apologized for the errors, said they were unintentional, and promised to pay the owners of 900,000 cars and SUVs for the difference in mileage.

For information, owners can go to www.hyundaimpginfo.com or www.kiampginfo.com.