The U.S. Environmental Protection Agency is now requiring the minimum four-gallon purchase at service station pumps selling a new 15-percent blend of the fuel additive ethanol from the same hose and nozzle as the current 10-percent blend known as E10.
The agency says it wants to keep consumers from miss-fueling outdoor power equipment - such as lawn mowers and snow throwers - with the 15-percent blend that's only approved for newer cars and trucks.
Without the rule, a contractor filling up a lawnmower who followed an E15 customer at the pump, but who only purchased two gallons of E10, could receive enough residual E15 from the hose and nozzle to violate an engine warranty and possibly cause engine problems.
Recently, a handful of service stations nationwide began offering E15, and more are expected to offer it as it becomes available.
Advocates say 40 to 15 percent reduces the nation's dependence on foreign oil, lowers the price of fuel and is good for the environment.
Critics say the 15 percent blend could cause premature engine failure and could lower gas mileage and void warranties of air-cooled engines used in outdoor power equipment.
About two-thirds of gasoline pumps use one hose and nozzle to dispense different blends of ethanol.
On its website, the EPA says service stations that offer E10 and E15 from the same hose and nozzle must use additional labeling to tell people about the minimum four-gallon purchase requirement - and to discourage small-engine owners from using the wrong fuel.
As more service stations offer E15 and pump technology evolves, the rule could be changed.
"For now, it's simply a placeholder to get things started. There are, for sure, going to be some stations that require a four-gallon minimum purchase with their equipment. But otherwise I think it will be fixed," said Robert White, director of market development for the Renewable Fuels Association, an ethanol advocacy group based in Washington, D.C.