Under the Renewable Fuels Standard passed in 2007, the Federal government requires certain volumes of ethanol to be blended into the U.S. transportation fuel supply.
However, states have discretion as to how much (or how little) ethanol goes into fuels sold within their borders.
And it turns out that relatively few states are doing much to encourage the sale of greater amounts of ethanol.
Ethanol-blended fuel can be found at many gas stations, but only a handful of states require it, according to a recent survey of laws conducted by Hemmings Motor News.
Only seven states--Louisiana, Minnesota, Missouri, Montana, Oregon, Pennsylvania, and Washington--have mandates that require ethanol to be blended with the fuel supply.
Louisiana and Washington require ethanol to make up 2 percent of the total volume of fuel sold, while the other states specify E10--a blend of 10 percent ethanol and 90 percent gasoline.
2011 Buick Regal flex-fuel badge
However, four more states--Minnesota, Montana, Oregon, and Pennsylvania--have ethanol mandates requiring local refineries to be able to produce certain minimum amounts of the fuel.
And some states--including Minnesota, Missouri, and Oregon--have exemptions for premium gasoline, or for fuel used in older vehicles.
Over the last decade-plus, a total of 14 states have reportedly tried to pass ethanol mandates, but apparently a 50-percent success rate is the best advocates can muster.
Two states passed ethanol mandates that were later repealed: Florida repealed its law in 2013, while Hawaii did away with its own rule earlier this year.
There have also been unsuccessful attempts to repeal ethanol mandates in four of the states that currently have them--Minnesota, Missouri, Oregon, and Pennsylvania.
While most states seem to have an ambivalent attitude toward boosting ethanol use, a few appear downright hostile to it.
Non-ethanol gasoline pump
Maine passed a law in 2013 that would ban the sale of corn-based ethanol if 10 other states, or a group of states with a total population of 30 million or more, did the same.
New Hampshire and Texas have toyed with bans as well, while North Carolina legislators have discussed eliminating the fuel tax on gasoline containing no ethanol.
Short of an outright ban, however, it's important to note that state legislation doesn't necessarily affect the availability of ethanol-blended fuels.
MORE: Flex-Fuel Vehicles And E85: Why Ethanol Isn't Making Its Numbers (Feb 2014)
Some states that don't mandate the sale of ethanol may even support it with incentives, or by purchasing "flex-fuel" vehicles for official use.
And the prevalence of informational labels about the possible presence of up to 10 percent ethanol in gasoline sold at pumps throughout the nation suggests that the biofuel is blended into quite a lot of the gasoline sold in the U.S.
State laws or not.