How a Plan to Boost Ethanol Would Reverberate Across the US

Ethanol, the intoxicating alcohol found in beer, wine and liquor, has been powering automobiles in the US since the era of the Model T. Beginning in the 1970s, when oil supplies were strained — and as worries rose about the environmental damage caused by fossil fuels — the US government adopted policies to encourage use of corn-based ethanol and other alternatives to petroleum-based gasoline. The governors of some corn-producing Midwest states are now demanding a policy change that would increase ethanol use in their region and have ripple effects across the nation, including on prices charged at service stations.

E10 gasoline, the most commonly sold blend in the US today, contains 10% ethanol. A 15% blend known as E15 is also available, but only at about 2,700 of the nation’s more than 150,000 filling stations, and it’s not allowed to be sold between June 1 and Sept. 15. That’s due to anti-pollution provisions in the Clean Air Act that limit gasoline’s volatility, or evaporative potential. (Summer heat boosts the evaporation of all liquids, including gasoline.) Excessive volatility is generally defined as a reading over 9 pounds per square inch of Reid vapor pressure (RVP). Even E10 normally exceeds that threshold, but in 1990, Congress granted it a waiver to go beyond RVP requirements by as much as 1 psi. Despite having a similar volatility, E15 has never received the same exemption via federal law.