Common Ethanol Fuel Mixtures - E10 or Less

E10 or Less

E10, a fuel mixture of 10% anhydrous ethanol and 90% gasoline sometimes called gasohol, can be used in the internal combustion engines of most modern automobiles and light-duty vehicles without need for any modification on the engine or fuel system. E10 blends are typically rated as 2 to 3 octane higher than regular gasoline and are approved for use in all new U.S. automobiles, and are mandated in some areas for emissions and other reasons. The E10 blend and lower ethanol content mixtures have been used in several countries, and its use has been primarily driven by the several world energy crises that have taken place since the 1973 oil crisis.

Other common blends include E5 and E7. These concentrations are generally safe for recent engines that run on pure gasoline. As of 2006, mandates for blending bioethanol into vehicle fuels had been enacted in at least 36 states/provinces and 17 countries at the national level, with most mandates requiring a blend of 10 to 15% ethanol with gasoline.

One way to measure alternative fuels in the U.S. is the "gasoline-equivalent gallons" (GEG). In 2002, the U.S. used as fuel an amount of ethanol equal to 137,000 terajoules (TJ), the energy equivalent of 1.13 billion gallons (4.3 billion liters) of gasoline. This was less than 1% of the total fuel used that year.

E10 and other blends of ethanol are considered to be useful in decreasing U.S. dependence on foreign oil, and can reduce carbon monoxide (CO) emissions by 20 to 30% under the right conditions. Although E10 does decrease emissions of CO and greenhouse gases such as CO₂ by an estimated 2% over regular gasoline, it can cause increases in evaporative emissions and some pollutants depending on factors such as the age of the vehicle and weather conditions. According to the Philippine Department of Energy, the use of not more than a 10% ethanol-gasoline mixture is not harmful to cars' fuel systems. Generally, automobile gasoline containing alcohol (ethanol or methanol) is not allowed to be used in U.S. certificated aircraft.