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. See pp. 10 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.

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 being 2 to 3 octane numbers higher than regular gasoline and are approved for use in all new U.S. automobiles, and mandated in some areas for emissions and other reasons.E10: Every vehicle's ethanol blend, drivingethanol.org.

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.Low-Level Ethanol Fuel Blends, Clean Cities fact sheet, April 2005. 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.E10 Emissions, U.S. Department of Energy. 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

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.Florida E85 Laws and Incentives , U.S. Department of Energy. 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.MTBE & Ethanol , State of Texas Energy Conservation Office. Mandatory blending of ethanol was approved in Mozambique, but the percentage in the blend has not been specified. South Africa approved a biofuel strategy in 2007, and mandated an 8% blend of ethanol by 2013. A 2007 Uruguayan law mandates a minimum of 5% of ethanol blended with gasoline starting in January 2015.Ley Nº 18.195: Agrofuels (in Spanish) - Parliament of Uruguay. 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.Ancap planea llevar de 2% a 5% mezcla con biodiesel - Diario El País, December 12, 2009 The Dominican Republic has a mandate for blending 15% of ethanol by 2015. Chile is considering the introduction of E5, and Panama, Bolivia and Venezuela of E10. India achieved the target of 10 percent ethanol blending, 5 months ahead of schedule, in June 2022. 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.Ngừng bán xăng RON 92 trên toàn quốc từ năm 2018 - Báo Điện Tử Chính Phủ, September 12, 2017 From June 2021, Argentina approved an E12 minimum (Law 27640), and after October 2022 a waiver for a maximum of E15.

+ Low ethanol blends used around the world (E5 to E25) Countries with mandatory blends or available for optional use (states where mandatory only) CountryEthanol blend Legal use CountryEthanol blend Legal use CountryEthanol blend Legal use StateEthanol blend StateEthanol blend Mandated See Table 1 pp. 10-11. Mandated Optional Optional Optional Optional Mandated Optional Mandated Mandated Mandated Optional Five provinces almost have reached full use of E10, while four provinces have only partly adopted the blend. Nine provinces Mandated Optional E10 use began in 2005 Mandated Mandated Mandated Introduction was delay for November 2009. Mandated Mandated Optional Mandated Mandated Mandated MandatedSince November 1, 2008 became available in some cities and will become mandatory in May 2009. Mandated Mandated See Table 4.1 MandatedMandated

A 2011 study conducted by VTT Technical Research Centre of Finland found practically no difference in fuel consumption in normal driving conditions between commercial gasoline grades 95E10 and 98E5 sold in Finland, despite the public perception that fuel consumption is significantly higher with 95E10. VTT performed the comparison test under controlled laboratory conditions and their measurements showed that over a distance of , the cars tested used an average of of 95E10, as opposed to of 98E5. The difference was 0.07 in favor of 98E5 on average, meaning that using 95E10 gasoline, which has a higher ethanol content, increases consumption by 0.7%. When the measurements are normalized, the difference becomes 1.0%, a result that is highly consistent with an estimation of calorific values based on approximate fuel composition, which came out at 1.1% in favour of E5.

Sweden + Reduction mandate of greenhouse emissions from fossil fuels in Sweden by means of biofuel mixtures (%) YearGasolineDieselJet kerosene20204.2 21 -20216.0 (1 Aug)26 (1 Aug)0.8 (1 July)20227.8 30.5 1.7 202310.1 7.8 **35 30.5 **2.6 202412.5 6*40 6*3.5 202515.5 6*45 6*4.5 202619 6*50 6*7.2 202722 *54 *10.8 202824 *58 *15.3 202926 *62 *20.7 203028 *66 *27 *) The reduction was reduced to the EU minimum level (6 percent for petrol and diesel) according to a bill by the Kristersson Cabinet in 2023.The Tidö Agreement.**)Further reduction was paused during 2023 based on a bill by the Andersson Cabinet. In Sweden, all 95-octane gasoline is E10 (6 to 10 percent of ethanol) since 1 August 2021, when the proportion of ethanol was increased from E5. In the early-mid-1990s, some fuel chains also sold E10. All newer and many older petrol cars bought in Sweden should handle this, since from January 2011, the Fuel Quality Directive (Directive 2009/30/EC) applied through its transposition into the law of Sweden as a member of the 27 member states of the EU.

E15

E15 contains 15% ethanol and 85% gasoline. This is generally the highest ratio of ethanol to gasoline that is possible to use in vehicles recommended by some auto manufacturers to run on E10 in the US. This is due to ethanol's hydrophilia and solvent power.

As a result of the Energy Independence and Security Act of 2007, which mandates an increase in renewable fuels for the transport sector, the U.S. Department of Energy began assessments for the feasibility of using intermediate ethanol blends in the existing vehicle fleet as a way to allow higher consumption of ethanol fuel. The National Renewable Energy Laboratory (NREL) conducted tests to evaluate the potential impacts of intermediate ethanol blends on legacy vehicles and other engines. In a preliminary report released in October 2008, the NREL presented the results of the first evaluations of the effects of E10, E15 and E20 gasoline blends on tailpipe and evaporative emissions, catalyst and engine durability, vehicle driveability, engine operability, and vehicle and engine materials. This preliminary report found none of the vehicles displayed a malfunction indicator light as a result of the ethanol blend used; no fuel filter plugging symptoms were observed; no cold start problems were observed at and laboratory conditions; and as expected, computer technology available in newer model vehicles adapts to the higher octane causing lower emissions with greater horsepower and in some cases greater fuel economy. NREL/TP-540-43543, ORNL/TM-2008/117

Other sources make the opposite claim about fuel economy. According to Consumer Reports, "ethanol isn’t as energy-dense as regular gasoline so you will see worse fuel economy with E15 gas.”

In March 2009, a lobbying group from the ethanol industry, Growth Energy, formally requested the U.S. Environmental Protection Agency (EPA) to allow the ethanol content in gasoline to be increased from 10% to 15%. Organizations doing such studies included the Energy Department, the State of Minnesota, the Renewable Fuels Association, the Rochester Institute of Technology, the Minnesota Center for Automotive Research, and Stockholm University in Sweden.

In October 2010, the EPA granted a waiver to allow up to 15% of ethanol blended with gasoline to be sold only for cars and light pickup trucks with a model year of 2007 or later, representing about 15% of vehicles on U.S. roads. In January 2011, the waiver was expanded to authorize use of E15 to include model year 2001 through 2006 passenger vehicles. The EPA also decided not to grant any waiver for E15 use in any motorcycles, heavy-duty vehicles, or nonroad engines because current testing data do not support such a waiver. According to the Renewable Fuels Association, the E15 waivers now cover 62% of vehicles on the road in the US, and the ethanol group estimates if all 2001 and newer cars and pickups were to use E15, the theoretical blend wall for ethanol use would be approximately 17.5 billion gallons (66.2 billion liters) per year. The EPA was still studying if older cars can withstand a 15% ethanol blend.