The U.S. Environmental Protection Agency (EPA) is struggling with Congress and various corporate interests over the amount of ethanol that will be blended into the U.S. fuel supply.

The Renewable Fuel Standard in place since 2007 calls for specific volumes of ethanol, but critics have tried to cap that amount while the EPA has tried to maintain or raise it.

Regardless of which side ultimately prevails, at least some ethanol will remain blended into most of the gasoline sold in the U.S.

DON'T MISS: EPA boosts required 2017 ethanol volume above expected level

That's because most U.S. gas stations already sell E10—a blend of 10 percent ethanol and 90 percent gasoline—as their default "regular" fuel.

So what future does ethanol-free gasoline have in the U.S.?

In its recent ruling on 2017 ethanol volumes, the EPA said ethanol-free gasoline—also known as E0—was on the decline, and that it considers the fuel only a niche product from now on, according to Hemmings Daily.

Big square baler harvesting wheat straw for production of cellulosic ethanol

The EPA is now calling for 19.2 billion gallons of ethanol to be blended with U.S. gasoline in 2017.

That represents an increase of 1.2 billion gallons over the amount for 2016, and is also higher than the 18.8 billion gallons originally proposed by the EPA in May.

In comparison, the EPA expects just 200 million gallons of E0 fuel to be consumed in 2017, mostly by recreational boaters.

ALSO SEE: Bill to cap ethanol in U.S. fuel supply gains momentum

Both the National Marine Manufacturers Association and American Motorcycle Association have expressed concern over the past few months that ethanol-free gasoline would no longer be available, according to Hemmings.

The EPA noted that the 200-million gallon figure is not a hard limit, and that consumer demand could lead to larger amounts of E0 being distributed.

But to reach the EPA's targets, any increase in E0 sales volume would have to be balanced by sales of fuels containing more ethanol.

Non-ethanol gasoline pump, with Six Month Road Test Hyundai Veloster

Alongside the 200 million gallons of E0, the EPA expects 275 million gallons of E85 and 728 million gallons of E15 to be dispensed in 2017.

E85 fuel is a blend of 85 percent ethanol and 15 percent gasoline that can only be used in specially-equipped "flex-fuel" vehicles.

MORE: EPA proposes to add more ethanol blends to 'Flex Fuel' category

The EPA previously declared E15—15 percent ethanol, 85 percent gasoline—to be suitable for use in all cars built in 2001 or later, although some automakers and mechanics have disputed that.

While the Renewable Fuel Standard calls for fixed volumes of ethanol to be blended with the fuel supply, a commercial market for this ethanol hasn't materialized.

"Flex-fuel" vehicles still make up a relatively small portion of the population on U.S. roads, and gas-station operators have been hesitant to incur the costs of selling blends with higher ethanol percentages due to anticipated low demand.

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