Biodiesel Basics

Biodiesel is a growing part of our fuel supply, but its potential as an oil-saving solution depends on what it’s made from.

Published May 2, 2012 Updated Oct 14, 2016

Biodiesel tanks at a biodiesel plant
United Soybean Board/Flickr, CC BY 2.0

What is biodiesel?

Biodiesel is a renewable fuel derived from vegetable oil or animal fats that can be added to conventional diesel to create a blend or used on its own.

All of today’s diesel vehicles can use up to 5 percent biodiesel (“B5”), which is blended into conventional diesel under the specifications governing diesel fuel (ASTM specifications). On average, biodiesel accounted for about 3% of diesel in 2015.

Some trucks can use up to a 20 percent biodiesel blend, but distribution challenges associated with marketing different blends for different vehicles have limited the adoption of these higher blends.

What is biodiesel made from?

In the United States, the majority of biodiesel is made from soybean and other edible vegetable oils, although biodiesel made from used cooking oils, animal fats, and wastes are also significant.

Image based on data from 2015

Global warming and biodiesel: it depends

The global warming pollution created by biodiesel depends on how it is made and (especially) what it is made from.

Biodiesel made from waste materials or used cooking oil can cut global warming pollution by 80 to 90 percent relative to conventional diesel fuel.

Biodiesel made from unused cooking oil— soy, canola, or palm oil— is a less attractive option because it expands the global market for vegetable oil, a major driver of deforestation.

Unintended impacts of biodiesel

Production of biodiesel from sustainable low carbon sources like used cooking oil is an important and growing oil saving solution.

Unfortunately, policy-driven demand for biodiesel is exceeding the limited supply of low-carbon biodiesel sources, diverting vegetable oils from food markets and other uses.

Shifting these resources to biodiesel production creates a supply gap in food markets that’s then filled by palm oil—and that’s a problem. The production of palm oil destroys rainforests, causing severe social and environmental damage in Southeast Asia and the global climate.

Biodiesel can be clean if the scale is not too large

Using biodiesel made from recovered waste streams is a smart way to help reduce our oil use. But increasing biodiesel production beyond the availability of these resources causes severe problems.

These problems can be avoided by federal and state policies that ensure biodiesel demand does not exceed the availability of low carbon biodiesel sources.

Otherwise we risk sourcing biodiesel from dirty sources, undermining the potential of biodiesel as an oil saving solution.

Biodiesel vs petroleum diesel

“Renewable diesel,” like is closely related to biodiesel. Both are made from fats and oils, but renewable diesel is processed with hydrogen to remove all the oxygen, producing a hydrocarbon fuel that is effectively a diesel substitute. The same fats and oils can also be made into a substitute for jet fuel using a related process. Renewable diesel and bio-jet are commonly called “drop-in fuels.”

Drop-in renewable diesel or bio-jet are essentially indistinguishable from conventional diesel and jet fuel and can be blended at almost any level, making it an attractive option for military or airline use.

Because most renewable diesel and bio-jet produced today are made from the same oils and fats as biodiesel, the same limitations on the scale of these resources apply.

Biodiesel vs gasoline in cars and light trucks

For conscientious consumers who already own a diesel vehicle, filling up with biodiesel may reduce your overall global warming emissions, especially if your biodiesel supplier is focused on waste resources.

Keep in mind, however, that biodiesel and gasoline are not interchangeable fuels, and each carries their own advantages and disadvantages.

If you are purchasing a new vehicle, consider a hybrid or electric vehicle to save on fuel costs and minimize global warming pollution.

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