E15 is gasoline that is blended with up to 15% ethanol by volume to form a finished gasoline that con be used in a conventional vehicle but still use some renewable fuel.

E15 is not in very wide use but is being promoted as a blend by the EPA in the US to allow compliance with a rising mandate for renewable fuel blending.

Currently the market for ethanol blended gasoline is dominated by the lower-ethanol E10 grade - pretty much the standard grade across the US. With almost all gasoline at E10, additional blending of ethanol depends on either wider use of E15 or of the much higher E85.

Where E15 is sold it generally sells at a discount to E10 or "clear" (no-ethanol) gasoline, reflecting its slightly lower energy content.

Growth in E15 use faces a number of market hurdles, though supply continues to grow gradually:

• Seasonal limitations - E15 has (until recently) not been allowed in the warm summer months because of its higher volatility (tendency to evaporate), which results in higher hydrocarbon vapor emissions that can contribute to poor air quality.

• Retail availability - Typical corner gas stations don't have the ability to offer both E10 and E15 at the same site given a limited number of fuel storage tanks. So generally they will opt for the more popular E10. Providers of E85 have the flexibility to blend at the pump to provide E15, but there are very few of these sites and they generally attract customers interested in going fully to E85.