E15

E15 is a motor fuel blend containing 10.5 to 15 percent ethanol by volume, with the balance being conventional gasoline. The ethanol is typically produced from corn fermentation in the United States. The "E" denotes ethanol content, and the number indicates the percentage range rather than a fixed point, which reflects variation in seasonal blending practices and feedstock availability.

E15 occupies the middle ground in the ethanol fuel spectrum. Conventional gasoline contains no added ethanol; E10 (the most common retail blend in the US) contains up to 10 percent; E85 contains 51 to 83 percent ethanol and requires flexible-fuel vehicles. E15 sits between these, approved in the United States for vehicles manufactured from 2001 onward, though compatibility varies by model year and engine design. Older engines and certain fuel system materials, particularly some seals and gaskets designed for pure gasoline, can degrade when exposed to the higher ethanol content in E15.

The fuel was introduced into US markets gradually, with EPA approval for model year 2001 and newer vehicles in 2011. Retailers and fuel suppliers have adopted E15 unevenly; availability remains concentrated in corn-growing regions and areas with strong renewable fuel mandates. Pumps dispensing E15 must be clearly labeled, as misfueling older vehicles or non-road equipment like small engines and motorcycles can cause running problems, fuel system corrosion, and warranty disputes.

Performance and cost trade-offs

Ethanol has a higher octane rating than gasoline (approximately 113 compared to 87-93 for typical gasoline), so E15 supports slightly higher compression ratios and can reduce engine knock. However, ethanol contains roughly 27 percent less energy per unit volume than gasoline, so fuel economy typically drops 3 to 5 percent on E15 compared to E10. The retail price advantage of E15 over premium gasoline is inconsistent, depending on regional ethanol production capacity, crude oil prices, and blending margins.

E15 serves regulatory and environmental policy objectives in the United States, where the Renewable Fuel Standard mandates minimum volumes of ethanol blending. Fuel suppliers use E15 to meet these mandates while avoiding the operational and infrastructure costs associated with E85 distribution, which requires separate handling and tank systems due to ethanol's hygroscopic nature and corrosive properties.