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Biofuels Basics

Biofuels are transportation fuels such as ethanol and biodiesel that are made from biomass materials. These fuels are usually blended with petroleum fuels (gasoline and diesel fuel), but they can also be used on their own. Using ethanol or biodiesel means less gasoline and diesel fuel is burned, which can reduce the amount of crude oil imported from other countries. Ethanol and biodiesel are also cleaner-burning fuels than pure gasoline and diesel fuel.

What is ethanol?

Ethanol is an alcohol fuel made from the sugars found in grains such as corn, sorghum, and barley.

United States Department of Agriculture (USDA) research geneticists study switchgrass as a source of ethanol.
Switchgrass can yield almost twice as much ethanol as corn, estimates geneticist Ken Vogel, who is conducting breeding and genetics research on switchgrass to improve its biomass yield and its ability to recycle carbon as a renewable energy crop.
Photo by Brett Hampton.

Other sources of sugars to produce ethanol include

  • Sugar cane
  • Sugar beets
  • Potato skins
  • Rice
  • Yard clippings
  • Tree bark
  • Switchgrass

Most of the fuel ethanol used in the United States is distilled from corn. Scientists are working on ways to make ethanol from all parts of plants and trees rather than just grain. Farmers are experimenting with fast-growing woody crops such as small poplar and willow trees and switchgrass to see if they can be used to produce ethanol.

Ethanol is blended with gasoline

A biodiesel and standard gasoline pump
A standard gas and biodiesel pump.

Source: Stock photography (copyrighted)

Nearly all of the gasoline now sold in the United States is about 10% ethanol by volume. Any gasoline-powered engine in the United States can use E10 (gasoline with 10% ethanol), but only specific types of vehicles can use mixtures with fuel containing more than 10% ethanol. A flexible-fuel vehicle can use gasoline with ethanol content greater than 10%. The U.S. Environmental Protection Agency ruled in October 2010 that cars and light trucks of model year 2007 and newer can use E15 (gasoline with 15% ethanol). E85, a fuel that contains 51%–83% ethanol, depending on location and season, is mainly sold in the Midwest and can only be used in a flexible-fuel vehicle.

What is biodiesel?

Biodiesel is a fuel made from vegetable oils, fats, or greases—such as recycled restaurant grease. Biodiesel fuel can be used in diesel engines without changing the engine. Pure biodiesel is non-toxic, biodegradable, and produces lower levels of most air pollutants than petroleum-based diesel fuel. Biodiesel is usually sold as a blend of biodiesel and petroleum-based diesel fuel. A common blend of diesel fuel is B20, which is 20% biodiesel.

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Ethanol is made from biomass

Ethanol is a renewable biofuel because it is made from biomass. Ethanol is a clear, colorless alcohol made from a variety of biomass materials called feedstocks (the raw materials used to make a product). Fuel ethanol feedstocks include grains and crops with high starch and sugar content such as corn, sorghum, barley, sugar cane, and sugar beets. Ethanol can also be made from grasses, trees, and agricultural and forestry residues such as corn cobs and stocks, rice straw, sawdust, and wood chips. Ethanol is made from these feedstocks in several ways.

USDA researchers adding yeast to begin ethanol fermentation
 Microbiologist Nancy Nichols and biochemical engineer Bruce Dien add yeast to a bioreactor to begin ethanol fermentation. Bt and non-Bt corn hybrids were compared for ethanol yields.
Photo by Scott Bauer.

Photo Credit: Scott Bauer, USDA Agricultural Research Service (public domain)

Fermentation is the most common method for fuel ethanol production

The most common ethanol production processes today use yeast to ferment the starch and sugars in corn, sugar cane, and sugar beets. Corn is the main feedstock for fuel ethanol in the United States because of its abundance and low price. The starch in corn kernels is fermented into sugar, which is then fermented into alcohol.

Sugar cane and sugar beets are the most common feedstocks used to make fuel ethanol in other parts of the world. Because alcohol is made by fermenting sugar, sugar crops are the easiest ingredients to convert into alcohol. Brazil, the world's second-largest fuel ethanol producer after the United States, makes most of its fuel ethanol from sugar cane. Most of the cars in Brazil can run on pure ethanol or on a blend of gasoline and ethanol.

Cellulosic ethanol is a large potential source of fuel ethanol

Ethanol can also be produced by breaking down cellulose in plant fibers. This cellulosic ethanol is considered an advanced biofuel and involves a more complicated production process than fermentation. While large potential sources of cellulosic feedstocks exist, commercial production of cellulosic fuel ethanol is relatively small.

Trees, grasses, and agricultural residues are potential feedstocks for cellulosic ethanol production. Trees and grasses require less energy, fertilizers, and water to grow than grains do, and they can also be grown on lands that are not suitable for growing food crops. Scientists have developed fast-growing trees that grow to full size in 10 years. Many grasses can produce two harvests a year for many years without annual replanting. A company in the United States is using the corn cobs and stocks of corn plants to make cellulosic fuel ethanol.

History of ethanol

Model T car
Model T vehicle

Source: Stock photography (copyrighted)

In the 1850s, ethanol was a major lighting fuel. During the Civil War, a liquor tax was placed on ethanol to raise money for the war. The tax increased the price of ethanol so much that it could no longer compete with other fuels such as kerosene. Ethanol production declined sharply because of this tax, and production levels did not begin to recover until the tax was repealed in 1906.

The Model T ran on ethanol

In 1908, Henry Ford designed his Model T, a very early automobile, to run on a mixture of gasoline and alcohol. Ford called this mixture the fuel of the future. In 1919, when Prohibition began, ethanol was banned because it was considered an alcoholic beverage. It could only be sold when mixed with petroleum. Ethanol was used as a fuel again after Prohibition ended in 1933.

Ethanol is once again used to fuel automobiles

Ethanol use increased temporarily during World War II when oil and other resources were scarce. In the 1970s, interest in ethanol as a transportation fuel was revived as oil embargoes, rising oil prices, and growing dependence on imported oil increased interest in alternative fuels. Since that time, ethanol use and production has been encouraged by tax benefits and by environmental regulations that require cleaner-burning fuels.

In 2005, Congress enacted a Renewable Fuel Standard (RFS) that set minimum requirements for the use of renewable fuels, including ethanol. In 2007, the RFS renewable fuel use targets were set to rise steadily to a level of 36 billion gallons by 2022. Learn more about the history of ethanol in a timeline. In 2016, about 14 billion gallons of ethanol were added to the gasoline consumed in the United States.

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Uses of Ethanol

Ethanol as a transportation fuel

Did you know?

The Ford Model T had an engine capable of running on either gasoline or ethanol.

Nearly all gasoline sold in the United States contains ethanol.

gasoline pump

Source: Stock photography (copyrighted)

Pump label required for E15.

E15 label

Source: U.S. Environmental Protection Agency (public domain)

E10 and E15

The most common use of ethanol as a fuel is in mixtures of motor gasoline. Most of the gasoline sold in the United States contains some ethanol. The exact amount varies by region. In general, the ethanol content of motor gasoline does not exceed 10% by volume. Gasoline with 10% ethanol content is referred to as E10, and gasoline with 15% ethanol content is called E15. All gasoline vehicles can use E10. Currently, only light-duty vehicles with a model year 2001 or newer can use E15.

The U.S. Environmental Protection Agency (EPA) is responsible for developing and implementing the U.S. Renewable Fuel Standard (RFS) to ensure that transportation fuel sold in the United States contains a minimum volume of renewable fuel. EPA is developing processes and procedures for how ethanol blends greater than E10 can be sold at retail.


E85 is a gasoline-ethanol blend containing 51% to 83% ethanol, depending on geography and season, and is defined as an alternative fuel. Although most E85 use is in the Midwest, about 2,900 public E85 fueling stations are located around the country. Only flexible-fuel vehicles can use E85.

Flexible-fuel (flex-fuel) vehicles can run on any mixture of ethanol and gasoline up to E85. About 20 million flex-fuel vehicles are in use in the United States. Flex-fuel vehicles may have a badge or plaque on the body of the vehicle with terms such as E85, Flex Fuel, or FFV.

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Ethanol & the Environment

Ethanol is nontoxic and biodegradable

Ethanol production facility in South Bend, Indiana

Ethanol Plant in South Bend, Indiana

Source: Photo courtesy of Wikimedia Commons (public domain)

Unlike gasoline, pure ethanol is nontoxic and biodegradable, and it quickly breaks down into harmless substances if spilled. Chemical denaturants in fuel ethanol make up about 2% of fuel ethanol by volume, and many of the denaturants are toxic. Similar to gasoline, ethanol is a highly flammable liquid and must be transported carefully.

Ethanol can reduce pollution

Ethanol and ethanol-gasoline mixtures burn cleaner and have higher octane levels than pure gasoline, but they also have higher evaporative emissions from fuel tanks and dispensing equipment. These evaporative emissions contribute to the formation of harmful, ground-level ozone and smog. Gasoline requires extra processing to reduce evaporative emissions before blending with ethanol.

Producing and burning ethanol results in emissions of carbon dioxide (CO2), a greenhouse gas. However, ethanol is considered atmospheric carbon-neutral because corn and sugarcane, the two major feedstocks for fuel ethanol production, absorb CO2 as they grow and may offset the CO2 produced when ethanol is made and burned. Some ethanol producers burn coal and natural gas for heat sources in the fermentation process to make fuel ethanol, while some burn corn stocks or sugar cane stocks.

The effect that increased ethanol use has on net CO2 emissions depends on how ethanol is made and whether or not indirect impacts on land use are included in the calculations. Growing plants for fuel is a controversial topic because some people believe the land, fertilizers, and energy used to grow biofuel crops should be used to grow food crops instead.

The U.S. government is supporting efforts to produce ethanol with methods that use less energy than conventional fermentation and that use cellulosic biomass, which requires less cultivation, fertilizer, and pesticides than corn or sugar cane. Cellulosic ethanol feedstock includes native prairie grasses, fast growing trees, sawdust, and even waste paper.

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Biodiesel is made from vegetable oils and animal fats

Vegetable oil in a bottle
Vegetable Oil in a Bottle

Source: Stock photography (copyrighted)

Biodiesel is a renewable fuel that can be used instead of the diesel fuel made from petroleum. Biodiesel can be made from vegetable oils and animal fats.

In 2016, soybean oil was the source of about 55% of the total feedstock (raw material) used to produce biodiesel in the United States. Canola oil and corn oil were the source of about 22%, recycled grease about 13%, and animal fats about 10% of the total feedstock. Rapeseed oil, sunflower oil, and palm oil are other major sources of the biodiesel that is consumed in other countries.

Biodiesel is most often blended with petroleum diesel in ratios of 2% (B2), 5% (B5), or 20% (B20). Biodiesel can also be used as pure biodiesel (B100). Biodiesel fuels can be used in regular diesel engines without making any changes to the engines. Biodiesel can also be stored and transported using diesel fuel tanks and equipment.

History of biodiesel

Before petroleum diesel fuel became popular, Rudolf Diesel, the inventor of the diesel engine in 1897, experimented with using vegetable oil (biodiesel) as fuel.

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Uses of Biodiesel

Biodiesel as a transportation fuel

A bus powered by soybean oil
A Bus Powered by Soybean Oil

Source: Stock photography (copyrighted)

Most of the trucks, buses, and tractors in the United States use diesel fuel. Diesel fuel is a nonrenewable fuel made from petroleum. Using biodiesel fuel produces less pollution than using petroleum diesel fuel. Any vehicle that operates on diesel fuel can use biodiesel.

Biodiesel fuel has chemical characteristics similar to petroleum-based diesel, so it can be used as a direct substitute for diesel fuel. Biodiesel fuel can also be blended with petroleum diesel in any percentage without reducing vehicle fuel economy.

Biodiesel blends

Any diesel engine can use biodiesel at blend levels of 5% by volume (B5) or lower. A blend of 20% biodiesel with 80% petroleum diesel is known as B20. Some federal and state government fleets, such as school and transit buses, snowplows, garbage trucks, mail trucks, and military vehicles, use biodiesel. Public fueling stations that sell biodiesel blends to the public are available in nearly every state.

Low-level biodiesel blends like B2 and B5 are popular fuels in the trucking industry because biodiesel has excellent lubricating properties, so the blends can benefit engine performance.

Pure biodiesel (often called B100) and biodiesel blends are sensitive to cold weather and may require a special type of anti-freeze, just like petroleum-based diesel fuel. Biodiesel acts like a detergent additive, loosening and dissolving sediments in storage tanks. Because biodiesel is a solvent, B100 may cause rubber and other components to fail in older vehicles. This problem does not occur with biodiesel blends.

Biodiesel use has increased substantially since 2001

Because of biodiesel's environmental benefits, ease of use, and available subsidies, biodiesel use in the United States grew from about 10 million gallons in 2001 to 354 million gallons in 2007. Consumption dropped in 2008 and then increased in 2009. Consumption dropped to about 260 million gallons in 2010, as the federal excise tax credit for biodiesel blending expired. In 2011, the tax credit was extended for one year, and substantial quantities of biodiesel were used to meet the Renewable Fuels Standard. These factors contributed to an increase in consumption to 886 million gallons in 2011. Consumption has generally increased since 2012, reaching about 2.1 billion gallons in 2016.

In 2001, total world biodiesel consumption was about 0.3 billion gallons. In 2014, about 8.1 billion gallons of biodiesel were consumed in at least 50 countries, and 54% was consumed in five countries.

World biodiesel consumption, 2014

  Billion gallons Share of total
World total 8.1  
United States 1.5 19%
Brazil 0.9 11%
France 0.8 10%
Germany 0.6   8%
Indonesia 0.6   7%
All others 3.7 46%
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Biodiesel & the Environment

Biodiesel burns much cleaner than petroleum diesel

Bus powered by biodiesel

Biodiesal Powered Bus

Source: National Renewable Energy Laboratory (public domain)

Biodiesel is nontoxic and biodegradable. Compared to petroleum diesel fuel, which is refined from crude oil, biodiesel combustion produces fewer air pollutants such as particulates, carbon monoxide, sulfur dioxide, hydrocarbons, and air toxics. Nitrogen oxide emissions from burning a gallon of biodiesel may be slightly higher than emissions from burning a gallon of petroleum diesel.

Biodiesel use may reduce greenhouse gas emissions

The U.S. government considers biodiesel to be carbon-neutral because the plants that are the sources of the feedstocks for making biodiesel, such as soybeans and palm oil trees, absorb carbon dioxide (CO2) as they grow. The absorption of CO2 by these plants offsets the CO2 that forms while making and burning biodiesel. Most of the biodiesel produced in the United States is made from soybean oil. Some biodiesel is also produced from used vegetable oils or animal fats, including recycled restaurant oil and grease.

In some parts of the world, large areas of natural vegetation and forests have been cleared and burned to grow soybeans and palm oil trees to make biodiesel. The negative environmental effects of this land clearing and burning may be greater than the potential benefits of using biodiesel produced from soybeans and palm oil trees.