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(CNN) -- The federal government may require automakers to road test cars to ensure the accuracy of gas mileage claims, the Environmental Protection Agency confirmed Tuesday.

Currently, the EPA road tests 10 to 15 percent of new vehicles every year, but the other 85% are tested by the car companies themselves, typically through use of computer modeling, wind tunnels and treadmill-like tests.

But those methods have come under scrutiny.

Korea's Hyundai and Kia lowered fuel economy estimates for some 2012 and 2013 models after the EPA found discrepancies between agency results and data submitted by the company.

Mileage claims were lowered by 1 or 2 miles per gallon on most cars, but the Kia Soul was adjusted by 6 miles per gallon.

And Ford last month agreed to make a "goodwill payment" to owners of 2013- and 2014-model year hybrid vehicles and most 2014 Fiestas after the EPA challenged its mileage claims.

The answer, the EPA says, is to require car makers to conduct road tests.

"Some automakers already do this, but we are establishing a regulatory requirement for all auto makers," Chris Grundler, director of the EPA's Office of Transportation and Air Quality, told the Wall Street Journal.

The proposal has not been formalized, and would have to go through a lengthy public comment and review period.

"At this early stage, it is premature for us to speculate on what form a proposal may take," the agency said in a statement Tuesday. "EPA will engage interested stakeholders proactively before making any proposal."

The EPA said the wind tunnel and other tests are important to get repeatable, reliable data. But it said it is considering requiring road tests.

The Obama administration has pushed through significant changes in auto mileage requirements for passenger cars and light trucks, including SUVs, pickups and minivans, as a way to reduce U.S. oil consumption.

Related policies and consumer demand with gas prices going up have led to design changes, lighter vehicles, cleaner-burning engines and more gas-electric hybrid vehicles.

Cars that go further on a gallon of gas are also a big selling point with consumers looking to save money at the pump.

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