WASHINGTON  The Environmental Protection Agency said on Friday that cars and light trucks from the 2001 model year onward can safely use a blend of 15 percent ethanol mixed with gasoline, up from the 10 percent standard now in effect in much of the country. The decision expands the pool of vehicles that could use such a fuel to about 62 percent of the total on the roads.

But the practical impact of the announcement on the fuel blend, known as E15, was not clear. An announcement in October that newer cars, from the 2007 model year and later, could use the blend has so far had little impact on retailers or drivers. A new fuel requires multiple approvals from many agencies. And retailers are typically not set up to offer an additional grade of gasoline at their pumps: if they wanted to sell E15, they would have to stop selling something else.

The ethanol industry is facing a problem selling its product because overall gasoline sales are down even while ethanol production is up. In addition, while many cars have been manufactured that can run on an 85 percent ethanol blend, known as E85, very few gasoline retailers outside the Midwest actually sell the fuel. Auto makers had expressed concern that the E15 blend could harm cars’ seals, pumps and other fuel system components.

But on Friday, Lisa P. Jackson, the E.P.A. administrator, said the agency’s testing had found otherwise. “Recently completed testing and data analysis show that E15 does not harm emissions control equipment in newer cars and light trucks,” she said in a statement. “Wherever sound science and the law support steps to allow more home-grown fuels in America’s vehicles, this administration takes those steps.”