The U.S. Environmental Protection Agency will delay a decision that was expected in December on whether gasoline blended with up to 15 percent ethanol is safe for vehicles built for the 2001 to 2006 model years, a source familiar with the matter told Reuters on Friday.

The EPA wants up to one more month of testing on the effects of the so-called E15 gasoline on engines, according to the source, who did not want to be identified. The agency may announce as soon as Friday that it will delay its decision on E15 in older vehicles, the source said.

The need for more testing is not related to problems with the fuel, according to the source. There were issues with the cars that involved an exhaust leak from a small hole in a pipe that affected emission levels and spark plugs that were not properly replaced, the source said.

EPA officials could not immediately be reached for comment.

The EPA in October approved using E15 gasoline in cars made during 2007 or later. U.S. gasoline contains up to 10 ethanol.

The Energy Department was supposed to forward its test results at the end of this month on putting E15 in vehicles back to 2001, with an EPA decision on the higher ethanol blended fuel  in December.

EPA’s decision on using E15 on older vehicles now is not expected until January.

Many service stations are reluctant to offer E15 because most fuel pumps have not been certified to sell it. Service station owners could also be sued by consumers if E15 harms the engines of cars, boats and chainsaws.

To help clear any confusion with drivers, the EPA plans to place E15 labels on gasoline pumps.