Ethanol is an alternative fuel made from a variety of 

plant-based feedstocks collectively known as “biomass.” 

It is typically blended up to 10% with gasoline (E10) for 

use in conventional vehicles to meet state renewable fuel 

mandates and to reduce air pollution. Ethanol is also 

increasingly available in blends of 85% ethanol, 15% 

gasoline. Known as E85, it can be used in the more than 

six million flexible fuel vehicles (FFVs) driving on U.S. 

roadways today. Studies estimate that ethanol and other 

biofuels could replace more than 30% of gasoline demand 

in the United States by 2030.

Fuel ethanol contains the same chemical compound as 

beverage alcohol, but it is “denatured,” or made unpotable 

with a small amount of gasoline (or other denaturant), 

during the production process, so it is unsafe for human 

consumption. Like beverage alcohol, it is currently made 

by fermenting sugars derived from starch crops such as 

corn or found in plants like sugar cane. Ethanol can also 

be made from cellulosic materials, such as grass, wood, 

crop residues, or newspapers. However, this process is 

more technically challenging because these materials 

must first be broken down into component sugars. The 

first commercial plants for producing cellulosic ethanol 

are now being built.

Production 

How is corn ethanol produced?

Corn ethanol is produced in two ways: wet milling and 

dry milling. The primary difference between these processes is in the initial grain treatment. During dry milling, the entire corn kernel is ground into a powder, mixed 

with water to form a mash, then cooked with added 

enzymes that turn the starch into glucose, a sugar. For 

wet milling, the grain is soaked or “steeped” in hot water, 

a process that facilitates the separation of the grain into 

its component parts. 

Only the starch in grains is used to make ethanol. The 

remaining nutrients—protein, fiber, and oil—are used to 

create by-products. Wet mills produce corn oil and gluten meal, high fructose corn syrup, and starch, while dry 

mills produce dried distillers grains with solubles (DDGS), 

which are used as a livestock feed. Carbon dioxide is also 

a by-product of ethanol production that is sometimes 

captured and processed into a commercial-grade liquefied 

form.

What is cellulosic ethanol, and when will 

it be available? 

Cellulosic ethanol is made from the woody or structural parts of plants. Examples of these materials include 

agricultural residues, such as corn stover, cereal straws, 

and sugarcane bagasse; industrial waste, such as sawdust 

and paper pulp; forestry residues, such as small trees 

and excess wood; and energy crops, such as switchgrass, 

hybrid poplars, and willows, specifically grown for fuel 

production. The cell walls of these materials are comprised of long sugar chains (carbohydrates). The sugar in 

these cell walls is extracted through the introduction of 

enzymes or acids, and then converted to ethanol using 

micro-organisms. Due to the complex structure of the 

cell walls, it is more difficult to break cellulosic materials 

into sugar, making them more expensive to convert to 

ethanol. Even with its complexity, cellulosic ethanol 

holds the promise of reducing petroleum use and lifecycle 

greenhouse gases (GHGs), and, because it is made from 

non-food crops, cellulosic ethanol should not affect the 

food supply and should likely reduce impact on land 

and water.

Developing processes to economically break down cellulosic feedstock components is the focus of research now 

being conducted by the U.S. Department of Energy (DOE) 

and other government and industry groups. Studies are 

examining biochemical processes that use microorganisms and thermochemical methods (heat) to convert the 

cellulosic feedstocks into fuel.1

Cellulosic ethanol is not yet readily available; however, 

several commercial cellulosic ethanol production plants 

are in development. In 2007, DOE announced a multimillion dollar investment to build several cellulosic 

ethanol biorefineries to advance the commercial production of this and other biofuels.

Ethanol Basics

Fact Sheet October 2008

1 NREL. “Biomass Economy: Biorefineries.” 2006 Research Review. www.nrel.gov/research_review/pdfs/2002/31967b.pdf.
Vehicle Applications

What are the different ethanol blends, and 

can they be used in any vehicle? 

Nearly half of U.S. gasoline contains up to 10% ethanol. 

The U.S. Environmental Protection Agency (EPA) classifies 

low-level ethanol blends (up to E10) as “substantially similar” to gasoline, meaning that they can be used legally in 

any gasoline-powered vehicle without modification.

E85 is considered an alternative fuel under the Energy 

Policy Act of 1992. It can be used in E85-capable FFVs, 

which are available in a variety of models produced by 

domestic and foreign automakers. As of August 2008, 

E85 is available at 1,528 fuel stations in 43 states.2

Intermediate ethanol blends, which are composed of 

more than 10% and less than 85% ethanol, are becoming 

available in limited areas. These blends can only be used 

in FFVs. 

How do FFVs differ from conventional vehicles?

There are several differences between FFVs and gasolinepowered vehicles. The fuel-system components are made 

of ethanol-compatible materials, and the control-system 

elements are modified to handle the variable combustion 

characteristics of the various gasoline/ethanol mixtures 

that can be used in FFVs. Figure 1 shows the specialized 

components of an FFV.

Can I convert my car to run on E85? 

Converting a conventional gasoline vehicle to run on E85 

is technically possible. But to legally do so, only conversions that have an EPA Certificate of Conformity can be 

performed. In California, conversions must also be certified by the California Air Resources Board (CARB). 

To date, certified FFV conversions are very limited. Using 

non-EPA-certified conversions is illegal and may affect 

vehicle warranties. To verify that a conversion system 

is legal for use in the United States and is compatible 

with their specific vehicles, consumers should request a 

copy of the supplier’s EPA Certificate of Conformity or 

CARB Executive Order when considering converting their 

vehicles.

All major U.S. automakers as well as a few foreign manufacturers offer numerous FFV models at little or no incremental cost compared to a standard gasoline vehicle. 

Therefore, purchasing a new or used FFV produced by an 

original equipment manufacturer is a convenient option 

for vehicle owners looking for E85 compatibility. 

What does the higher-octane level of E85 

mean in terms of vehicle performance?

Octane rating is a measure of auto ignition resistance 

sometimes referred to as “knock resistance.” The right 

amount of octane ensures that combustion occurs at the 

right time, delivers the most efficient power, and protects 

Fuel filler assembly: 

Anti-siphon and spark 

arrestor features are 

included to handle 

ethanol’s increased 

conductivity

Fuel rail and fuel lines: Must be made of 

ethanol-compatible materials with seals, 

gaskets, and rubber fuel hoses rated for 

ethanol use

Fuel tank: Must be made of 

ethanol-compatible materials and 

designed to minimize evaporative 

emissions from ethanol

Fuel system electrical connections and wiring: 

Must be electrically isolated and made of materials 

designed to handle ethanol’s increased conductivity 

and corrosiveness (if exposed to fuel)

Internal engine parts: Piston 

rings, valve seats, valves, and 

other components must be made 

of ethanol-compatible materials 

that are designed to minimize 

the cleansing effects of alcohol 

fuels, which can wash lubrication 

from parts

Fuel identifier system: 

Automatically senses the 

composition of the fuel and 

adjusts engine for varying 

ethanol-gasoline blends Fuel injection system: Must be made of 

ethanol-compatible materials and designed 

for higher flow to compensate for ethanol’s 

lower energy density

Fuel pump assembly: In-tank components 

must be made from ethanol-compatible 

materials and sized to handle the increased 

fuel flow needed to compensate for ethanol’s 

lower energy density

Engine calibration updates: 

Fueling and spark advance calibrations 

directed by vehicle computer to control 

combustion, enable cold start, and 

meet emissions requirements

Figure 1. FFV Components

2 NREL. Alternative Fueling Station Locator. www.eere.energy.gov/afdc/fuels/stations_locator.html. Alternative Fuels and Advanced Vehicles 

Data Center. August 2008. 

Clean Cities

October 2008
the engine from damage. Higher octane does not necessarily translate into higher horsepower. Technically, it can 

“allow” more horsepower if the engine and engine control 

system are designed to provide enough fuel and air and 

can optimize the combustion process to take advantage 

of the higher octane levels. However, current FFVs are 

typically optimized for gasoline and designed so drivers 

don’t really notice a decrease in power or performance 

when the vehicle is running on E85.

Do miles-per-gallon ratings drop when 

ethanol is used in place of gasoline?

Yes, because ethanol contains less energy per gallon than 

gasoline. A gallon of 100% ethanol contains 76,000 British 

Thermal Units (BTUs) of energy, whereas a gallon of gasoline contains around 110,000 BTUs of energy. The number 

of miles per gallon will drop in direct proportion to the 

energy contained in the fuel, which amounts to a 25% 

reduction in the miles delivered per gallon of E85 versus 

gasoline.3 However, if E85 is priced below gasoline, the 

cost-per-mile to operate may be comparable. For E10, the 

energy difference is only a few percent and typically not 

noticed in the vehicle’s mileage performance.

Energy Balance

How much energy does it take to produce 

corn ethanol? 

Corn ethanol’s net energy value (NEV) is defined as 

the difference between the amount of energy available 

in a gallon of corn ethanol and the amount of fossil 

energy it takes to grow corn and process it into that 

gallon of fuel. 

Assumptions in the NEV calculation include: 

•	 Corn yields and crop inputs, such as fertilizers;

•	 Efficiencies in corn-to-fuel conversion technologies;

•	 Types of energy used to produce the ethanol;

•	 Credits for the energy available in the coproducts; and

•	 Range of factors used in production lifecycle

evaluations. 

NEV values are based on the amount of fossil energy used 

(i.e., petroleum, natural gas, coal) and do not include 

renewable energies (i.e., sunlight, biomass) used for 

growing corn or in biorefineries to generate heat used 

in the production process. This is primarily done for the 

purpose of evaluating ethanol as a viable replacement 

fuel for gasoline. 

The NEV of corn ethanol production is improving as 

technology evolves. Although corn ethanol’s NEV has 

been debated for years, the majority of studies published 

since the early 1990s show that corn ethanol can provide 

between 1.3 and 1.7 times more energy than the fossil 

energy it consumes during its production lifecycle.4

This means that for every unit of energy delivered at the 

pump, corn ethanol production only requires 0.78 units 

of fossil energy, according to research conducted by DOE’s 

Argonne National Laboratory (ANL).

The energy used to produce ethanol can also be compared 

to gasoline. Compared to the 0.78 units of fossil fuel 

required for corn ethanol production, gasoline requires 

1.23 units. This means that the use of corn ethanol results 

in the consumption of 40% less fossil energy than the 

gasoline it replaces.5

Figure 2 shows the amount of fossil energy required to 

provide 1 BTU of each fuel at the pump. The graph does 

not reflect energy derived from solar or other renewable 

sources used in ethanol production. 

Moving forward, cellulosic ethanol has an even higher 

energy balance than corn ethanol—delivering six times as 

much energy as is necessary to produce it. That’s why DOE 

is focusing on research to develop processes to efficiently 

break down cellulosic feedstock components. 

Figure 2. Fossil Energy Requirements for Gasoline and Corn and 

 Cellulosic Ethanol (2007)

BTU

2

1.5

1.0

0.5

0.0

Gasoline Corn Ethanol Cellulosic Ethanol

Fossil BTU = 1.23

Fossil BTU = 0.74

Fossil BTU ~ 0.1

From Coal and Natural Gas From Petroleum

3 NREL. “Flexible Fuel Vehicles: Providing a Renewable Fuel Choice.” Alternative Fuels and Advanced Vehicles Data Center. www.eere.energy.

gov/afdc/pdfs/42953.pdf.

4 ANL. “Ethanol: The Complete Energy Life-Cycle Picture.” www.transportation.anl.gov/pdfs/TA/345.pdf.

5 ANL. “Ethanol: The Complete Energy Life-Cycle Picture.” www.transportation.anl.gov/pdfs/TA/345.pdf.

Clean Cities

October 2008

Source: “Energy Balance of Gasoline and E85” (ANL) 
Figure 3 illustrates the timeline of significant reports published on ethanol’s NEV. Most of these studies found that 

ethanol has a positive NEV and their results are supported 

and used by DOE and the U.S. Department of Agriculture 

(USDA). 

Greenhouse Gas Emissions

How do ethanol greenhouse gas emissions 

compare to those of gasoline?

For a picture of the true greenhouse gas (GHG) reduction, 

lifecycle analyses are used to calculate GHG emissions at 

each step of production and use. For ethanol, these steps 

include growing the feedstock crops, transporting the 

feedstock to the production plant, producing and distributing the ethanol, and consuming it in vehicles. For 

gasoline, crude oil must be extracted from the ground, 

transported to a refinery, refined, distributed, and consumed in vehicles.

6 Wang, M.; May Wu; Huo H. (May 2007) “Life-Cycle Energy and Greenhouse Gas Emission Impacts of Different Corn Ethanol Plant Types.” 

Environmental Research Letters. Volume 2, Number 2.

7 EPA. “Renewable Fuel Standard Program: Draft Regulatory Impact Analysis.” www.epa.gov/oms/renewablefuels/420d06008.pdf.

Recent analysis conducted by ANL6 shows that when 

entire fuel lifecycles are considered, using corn ethanol 

instead of gasoline reduces GHG emissions by 19%-52% 

depending on the energy source used during ethanol 

production and the coproducts of the process. Biofuels 

produced using sustainable practices offer a significantly 

greater reduction in GHG emissions. 

The fuel used to produce the energy used in the process has a significant impact on the GHG emissions (see 

Figure 4). Burning natural gas is much less GHG-intensive 

than coal because it contains substantially less carbon 

than coal per hydrogen carbon (energy producing) bond. 

Biomass emits fewer GHGs than natural gas because it 

actually pulls carbon dioxide out of the air when they 

are in the growth stages of its lifecycle.

Of the 102 ethanol production facilities operating in 

2006, 98 used natural gas, two used coal, one used coal 

Figure 3. Timeline of Significant Ethanol NEV Studies

Source: Ethanol: “The Complete Energy Life-Cycle Picture” (ANL) 

60,000

40,000

20,000

0

-20,000

-40,000

-60,000

-80,000

-100,000

-120,000

Net Energy Value (BTU/gallon)

Energy balance is defined as BTU content in a gallon of ethanol minus fossil energy used to produce a gallon of ethanol

1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2007

Chambers et al.

Weinblatt et al.

Marland & Turnollow

Ho

Shapouri et al.

Wang et al.

Lorenz & Morris

Agri. & Agri.

Food Canada

NR Canada

Shapouri et al.

Kim &

Dale

Kim &

Wang Dale

Wang Graboski Delucchi

Hill

Farrell

Pimentel

Pimentel Pimentel

& Patzek Pimentel

Keeney & DeLuca

Patzek

Clean Cities

October 2008
and biomass, and one used syrup from the process to 

produce steam.7

Questions have also been raised about the impacts on 

GHGs if ethanol production results in direct or indirect 

land-use changes. This is an issue that is not yet wellunderstood, but the United States government is working 

to ensure ethanol production is sustainable. For example, 

as part of the Renewable Fuels Standard, the Energy 

Independence and Security Act of 2007 (EISA) requires 

EPA to enhance its GHG lifecycle analysis methodology for biofuels to include direct and indirect land use 

changes.

Food and Fuel 

What effect does fuel ethanol have on food prices? 

Estimates of the impact of biofuels on food prices vary 

widely. Many factors contribute to high retail food prices, 

including corn ethanol production. Other factors contributing to rising global food prices include: 

•	 Higher costs of fossil fuels used to transport food to

retail outlets,

•	 Increased demand as emerging economies grow and

populations adopt better diets and eat more meat,

•	 Adverse weather in parts of the world and droughts

leading to poor harvests,

•	 Devaluation of the dollar, which may reduce importing

costs and increase export buying,

•	 Reduced global grain supply and increased demand for

U.S. agricultural exports,

•	 Hedge funds and index funds buying of grain and

oilseed futures,

•	 Growth in foreign exchange holdings by major food

importing countries, and

•	 Reduction in global agriculture research and development slowing pace of yield increases.

The majority of U.S.-produced ethanol is currently made 

from field corn, which is grown to feed livestock. The production process yields coproducts of distiller’s grains and 

gluten feed—both of which are fed to livestock, which 

helps minimize the impact on meat production. Wet-mill 

ethanol production facilities also produce starch, corn 

sweeteners, and corn oil—all of which are used as food 

ingredients for human consumption.

Does the use of ethanol impact gasoline prices? 

According to recent reports, ethanol’s production and 

increased availability is helping keep gasoline prices lower 

than they otherwise would be. The following excerpts 

support this theory.

•	 “The growth in ethanol production has caused retail

gasoline prices to be $.20 to $.40 per gallon lower than 

would otherwise been the case.”8

•	 “Oil and gas prices would be about 15% higher if biofuel

producers weren’t increasing their output.”9

•	 “The use of 10% ethanol blend saved Missouri drivers

$.077 per gallon at the retail pump in 2007.”10

Water Impacts

Are there water-quality impacts associated 

with increased corn-crop acreages and the 

use of fertilizers and pesticides?

Increased land allotted for corn production and the use 

of fertilizers and pesticides to accelerate corn yields can 

result in higher amounts of nitrogen and phosphorous 

in waterways. In concentrations that are too high, these 

compounds can pollute waterways through surface runoff 

and groundwater. However, new water-conservation practices and fertilizer-efficiency techniques are now being 

used to increase corn yields and reduce agricultural water 

consumption and pollution. As required by EISA, EPA 

will monitor this issue as part of its assessment of the 

environmental impacts of biofuels and will publish a 

report on this topic in 2010.

8 Du, X.; Hayes D.J.; “The Impact of Ethanol Production on U.S. and Regional Gasoline Prices and on the Profitability of the U.S. Oil 

Refinery Industry.” 08-WP 467. 2008.

9 “Wall Street Journal.” March 2008.

10 Urbanchuk, J.M. Impact of Ethanol on Retail Gasoline Prices in Missouri. www.mocorn.org/news/2008/LECG_MO_E10_Analysis.pdf.

Corn Ethanol Cellulosic

Natural

Gas

Gasoline

Petroleum Current

Average

Biomass Biomass

28%

Reduction

19%

Reduction

52%

Reduction

86%

Reduction

Clean Cities

October 2008

Source: “Life-Cycle Energy and Greenhouse Gas Emission Impacts

 of Different Corn Ethanol Plant Types” (ANL)
Relative to corn, the production of cellulosic biomass 

feedstocks require lower inputs of water, fertilizers, and 

pesticides, accompanied by less erosion and improved 

soil fertility.

How much water is required to produce 

one gallon of ethanol? 

According to a 2007 National Renewable Energy 

Laboratory (NREL) study,11 96% of the acreage used today 

to grow corn for ethanol has sufficient enough annual 

rainfall to not need supplemental irrigation. That is 

why corn is grown in humid climates like the Midwest, 

where very little supplemental irrigation is needed. Water 

required for the other 4% is approximately 1.2 acre-feet of 

water per acre, which is approximately 785 gal for every 

gallon of ethanol produced.

NREL’s study also found that on average, the production 

process to produce 1 gal of ethanol requires 3 gal of water, 

while 2.5 gal of water are needed to produce 1 gal of gasoline. These estimates do not include water resources used 

for exploration and oil recovery. 

Land Use and Soil Impacts

What impact does an increase in corn crops grown 

for ethanol production have on land use? 

Of the 130% increase in corn productivity over the past 

35 years, only 20% of the increase has come from expansion of crop land. Improved farming practices and new 

technologies are improving corn yields per acre, allowing 

growers to harvest considerably more corn without significantly increasing acreage. Biotech improvements to crop 

seeds have enabled farmers to adopt environmentally 

sensitive agricultural practices—such as no-till cultivation—that increase yields, while reducing the amount 

of water, fertilizer, and pesticide needed.

Potential land-use changes are an area of concern, 

however, reflected in EISA. The legislation expanded the 

national Renewable Fuel Standard to mandate 36 billion 

gal of biofuels annually by 2022. Of this, 21 billion gal 

must be advanced biofuels, which includes a requirement of 16 billion gal of cellulosic biofuel. Only biofuels 

made from feedstocks grown on land cleared for cultivation before December 2007 qualifies as advanced or cellulosic fuels under EISA. This provision was included to 

discourage detrimental land-use changes, such as tropical 

deforestation.

Growing cellulosic materials could require less fertilizer 

and land compared to growing corn. Higher fuel production rates for each ton of biomass decreases land use and 

requires significantly less water than corn ethanol. 

Will soil quality be impacted by the harvesting 

of agricultural residues for use as cellulosic 

ethanol feedstock?

Soils are complex ecosystems composed of unknown 

numbers of organisms. The impact of crop residue 

removal may have on crop production and soil properties 

is an area of U.S. government investigation. EISA contains a provision that allows only domestic and imported 

renewable fuels that don’t come from sensitive areas, and 

the USDA has invested $17 billion in programs requiring 

the adoption of environmental cropping practices since 

2002. 

Research is currently underway to determine how to 

combine residue collection with good soil conservation 

practices to maintain soil health. Two studies published 

so far are the USDA’s field report, “Soil Health as an 

Indicator of Sustainable Management,” and DOE’s document, “Breaking the Biological Barriers to Cellulosic 

Ethanol: A Joint Research Agenda.”

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, 

a cleaner environment, and greater energy independence for America. Working 

with a wide array of state, community, industry, and university partners, the 

U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy 

invests in a diverse portfolio of energy technologies.

DOE/GO-102008-2655 • October 2008

Printed with a renewable-source ink on paper containing at least 50% wastepaper, 

including 10% postconsumer waste.

Sponsored by the U.S. Department of Energy

Energy Efficiency and Renewable Energy 

Vehicle Technologies Program

For more information contact: EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov

Prepared by the National Renewable Energy Laboratory (NREL)

NREL is a national laboratory of the U.S. Department of Energy 

Operated by the Alliance for Sustainable Energy, LLC

For more information about Clean Cities visit www.eere.energy.gov/cleancities

Clean Cities

11 Aden, A.; “Water Usage for Current and Future Ethanol Production.” http://epw.senate.gov/public/index.cfm?FuseAction=Files.

View&FileStore_id=3d2f1427-d51d-4a54-8739-166853ee1c44.