The government has settled on a label for gas stations selling a blend of gasoline and ethanol called E15, which contains more ethanol -- grain alcohol -- than the E10 blend that's replaced pure gasoline at most stations.

The Environmental Protection Agency previously approved E15 -- 85% gasoline and 15% ethanol -- for use in vehicles back to 2001 models. The approved label is part of the EPA's final rule spelling out about how E15 can be sold and what standards it must meet.

E15 isn't available yet. EPA says sellers have to first register their blends with the agency to be sure they meet a number of standards. Probably nothing at stations until late this year, ethanol interests say.

EPA says tests show E15 won't harm 2001 and newer vehicles, which have hoses and gaskets and seals specially designed to resist corrosive ethanol. But using E15 fuel in older vehicles or in power equipment such as mowers, chainsaws and boats, can cause damage and now is literally a federal offense.

Growth Energy, representing ethanol interests, says cars 2001 and newer are 67.2% of the vehicles on the road and they use 75% of the fuel.

The just-approved label is meant to warn people away from misusing the potentially troublesome E15 fuel, but it can't prevent misuse.

"If drivers mistakenly put E15 in their tanks and their vehicles aren't designed to burn it, they could risk damaging their engines. Car and truck owners with questions may contact their dealership's service department to determine any fuel restrictions," according to a cautionary note today from the National Automobile Dealers Association.

Automakers say misfueling also could lead to contentious wrangling with their customers over damage from alcohol fuel. The EPA rule "fails to require service station pumps contain a warning label directing consumers to check their owner's manual to determine the appropriate fuel for specific vehicles. This is a significant and unfortunate omission," says the Alliance of Automobile Manufacturers, a trade organization representing car companies.

Misfueling also might dirty the air. "If you put E15 into the wrong vehicle, or the wrong type of equipment, such as lawn mowers, it will put more pollution into the air," says Roland Hwang, transportation expert at the Natural Resources Defense Council.

Other concerns:

"In California, data show that even with E10 we're seeing an increase in emissions," Hwang says. "The alcohol reacts with soft materials, hoses, seals, and makes those more permeable, and allows evaporation of fuel," he says, acknowledging that "it's not a issue with newer vehicles."

California has many older cars, without ethanol-resistant parts, on the road because cars don't rust there, and because the state is a hotbed of auto hobbyists who maintain aging models.

Higher blends of alcohol -- ethanol in the U.S., nearly all of it made from corn -- cut the energy content of the fuel. Ethanol has only about two-thirds as much energy as gasoline does, so fuel economy and performance can suffer as the proportion of ethanol increases.

Growth Energy and 54 ethanol producers petitioned the EPA in 2009 to get approval for E15.