Ethanol is blended with gasoline in different quantities to cut down the consumption of petroleum fuels. Ethanol fuel blend is increasingly used as oxygenated additive for standard gasoline as replacement for MTBE which contaminate underground water. Because of its high percentage of oxygen (35%), Ethanol helps a more complete combustion of gasoline, thus reducing harmful emissions.

Pure ethanol reacts with or dissolves certain rubber and plastic materials and cannot be used in unmodified engines. Pure ethanol has higher octane rating than ordinary gasoline and requires changes to compression ratio or spark time to obtain maximum benefit. A larger carburetor jets is needed to change pure gasoline fuelled car into a pure ethanol fuelled car. A cold starting system is also required to ensure sufficient vaporization and minimize uncombusted non vaporized ethanol. No engine modification is necessary for only l0-30% ethanol is mixed with gasoline.

The most common forms of ethanol blends are:

1. El0 gasohol (containing l0% ethanol) is the most common variant - is introduced throughout the country in Denmark and commonly available in Midwestern U.S.A. El0 is intended as a fuel additive rather than a fuel alternative
2. E85 (contains 85% ethanol and l5% gasoline) is used in Flexible fuel vehicles (FFV) - vehicles that re specially manufactured with changes to their engines and fuel delivery systems to run on higher percentages of ethanol. E85 is used as a fuel alternative.