Washington ? The Obama administration on Wednesday approved a 50 percent increase in the amount of ethanol used in fuel blends, but only for newer vehicles, a decision critics say could confuse consumers.

The Environmental Protection Agency said it will allow blends to include as much as 15 percent ethanol, up from the current 10 percent limit. The ruling is part of an effort to reduce the nation’s reliance on fossil fuels and cut down on oil imports.

Yet a 15 percent blend is not deemed suitable for older vehicles, so consumers will have to be careful.

The EPA said gas stations will be required to clearly label their pumps to prevent customers from buying the wrong fuel.

The agency said the so-called E15 blend should only be used in vehicles built in 2007 or later. The blend should not be used for cars and trucks made before 2001. They were not designed for higher ethanol blends and are more liable to damage.

The agency is still reviewing data on vehicles made from 2001 to 2006, with results expected in November.

To mitigate the impact of its decision, the agency said it would not mandate that gas stations offer the E15 blend.

“Ultimately it will be up to fuel suppliers and retailers to make it available,” said Gina McCarthy, a senior EPA administrator. “It’s by no means assured the market will develop quickly.”

The risk of consumer confusion and potential legal liabilities has spurred a number of groups, such as auto makers, boat builders and refiners, to oppose the EPA ruling.

“The large majority of today’s vehicle warranties only cover gasoline with up to 10 percent ethanol,” said spokesman Bob Greco of the American Petroleum Institute.

“More ethanol in gasoline could result in the voiding of customer warranties.”

Those groups have been joined by a motley crew of other foes such as livestock ranchers and environmentalists.

Their concerns are far-ranging. Refiners lament the cost and complexity of supplying different blends to gas stations. Ranchers worry it will drive up costs as farmers shift away from growing corn for feed. Environmentalists say higher blends will lead to the clearing of more land.

Supporters of higher ethanol blends, for their part, say it will reduce the nation’s dependency on foreign suppliers of oil and keep more U.S. dollars at home, helping the domestic economy.

Under federal law, the U.S. is supposed to double the amount of alternative fuels by 2022. Ethanol, a byproduct of corn, is the most readily available source.

Corn growers in the Midwest, led by agricultural giant Archer Daniels Midland Co., have urged the EPA to boost the limit. Many lawmakers from that region — in both parties — have also pushed for an increase. They’ve supported long-standing subsidies for ethanol.