Common ethanol fuel mixtures

thumb|upright=1.35|Summary of the main ethanol blends used around the world in 2013

Several common ethanol fuel mixtures are in use around the world. The use of pure hydrous or anhydrous ethanol in internal combustion engines (ICEs) is only possible if the engines are designed or modified for that purpose, and used only in automobiles, light-duty trucks and motorcycles. Anhydrous ethanol can be blended with :gasoline (petrol) for use in gasoline engines, but with high ethanol content only after engine modifications to meter increased fuel volume since pure ethanol contains only 2/3 of the BTUs of an equivalent volume of pure gasoline. High percentage ethanol mixtures are used in some racing engine applications as the very high octane rating of ethanol is compatible with very high compression ratios.

Ethanol fuel mixtures have "E" numbers which describe the percentage of ethanol fuel in the mixture by volume, for example, E85 is 85% anhydrous ethanol and 15% gasoline. Low-ethanol blends are typically from E5 to E25, although internationally the most common use of the term refers to the E10 blend.

Blends of E10 or less are used in more than 20 countries around the world, led by the United States, where ethanol represented 10% of the U.S. gasoline fuel supply in 2011. Blends from E20 to E25 have been used in Brazil since the late 1970s. E85 is commonly used in the U.S. and Europe for flexible-fuel vehicles. Hydrous ethanol or E100 is used in Brazilian neat ethanol vehicles and flex-fuel light vehicles and hydrous E15 called hE15 for modern petrol cars in the Netherlands.

Other common blends include E5 and E7. These concentrations are generally safe for recent engines that should 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 measure of alternative fuels in the U.S. is the "gasoline-equivalent gallon" (GEG). In 2002, the U.S. used as motor fuel, ethanol equal to , the energy equivalent of 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 up to 10% ethanol-gasoline mixture is not harmful to cars' fuel systems. Generally, automobile gasoline containing alcohol (ethanol or methanol) is not recommended to be used in aircraft.

Availability

thumb|E10 Logo required on [[Delaware fuel dispensers]]

E10 became the standard fuel at petrol stations in the United Kingdom as of September 2021.
E10 was introduced nationwide in Thailand in 2007, and replaced 91 octane pure gasoline in that country in 2013.
E10 is commonly available in the Midwestern United States. It was also mandated for use in all standard automobile fuel in the state of Florida by the end of 2010. Due to the phasing out of MTBE as a gasoline additive and mainly due to the mandates established in the Energy Policy Act of 2005 and the Energy Independence and Security Act of 2007, ethanol blends have increased throughout the United States, and by 2009, the ethanol market share in the U.S. gasoline supply reached almost 8% by volume.
Mandatory blending of ethanol was approved in Mozambique, but the percentage in the blend has not been specified. The monopolic, state-owned fuel producer ANCAP started blending premium gasoline with 10% of bioethanol in December 2009, which will be available in all the country by early January 2010.
The Dominican Republic has a mandate for blending 15% of ethanol by 2015.
From January 2018, all 92-octane fuel in Vietnam is mandated to contain 5 percent ethanol (E5). No ethanol blending is required for 95-octane fuel.
From June 2021, Argentina approved an E12 minimum (Law 27640), and after October 2022 a waiver for a maximum of E15.

{| class="wikitable sortable" style="margin: 1em auto 1em auto"

! colspan="13" style="text-align:center;" | Low ethanol blends used around the world (E5 to E25)

| colspan="6" style="text-align:center; background:#cfc;" | Countries with mandatory blends or available for optional use

| colspan="3" style="text-align:center; background:#cfc;" |

| colspan="4" style="text-align:center; background:#cfc;" | (states where mandatory only)

! style="background:#bfb;" | Country