WASHINGTON (Reuters) - A leading U.S. oil industry group will petition the Supreme Court to take up a case over the Environmental Protection Agency's approval of higher ethanol blends for older cars, a source said on Thursday.

The American Petroleum Institute will announce the petition in a call on Thursday, the source said.

A U.S. federal appeals court last month denied a request by food and oil groups that it reconsider a decision upholding a federal measure allowing gasoline to be mixed with a higher percentage of ethanol, producing a blend known as E15. The API says that tests show E15 can damage engines.

(Reporting by Timothy Gardner; Editing by Gerald E. McCormick)