What Generation Is Your Biodiesel?

University of Idaho yellow Volkswagen bug fueled on mustard oil biodiesel

U. of Idaho Volkswagen bug fueled on mustard oil biodiesel. Photo: http://biodieseleducation.org


Biodiesel Definitions under the Renewable Fuel Standard
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For Additional Information


It has become popular lately to refer to biofuels as “first generation,” “second generation,” “third generation,” and so on.

  • First generation biofuels consist of ethanol from sugar or starch (such as from corn) and biodiesel from animal fats and vegetable oils.
  • Second generation biofuels are those produced from ligno-cellulosic materials such as switchgrass or wood chips. At this point the definitions get a little less well defined, but
  • Third generation is usually defined as fuels from algae, and
  • Fourth generation status is claimed by every new technology seeking to promote itself as the next big thing.

These terms have no real meaning—they are mainly marketing-speak, as Gerhard Knothe pointed out (Knothe, 2010). Biofuels producers using more unusual feedstocks may claim to be a higher “generation” than biofuels from more common feedstocks such as soy oil or waste grease. In fact, in a blog post, we explain how the use of the “generational” terms can be misleading.

In reality, the “generational” terms are not used in any official context, such as the Environmental Protection Agency’s Renewable Fuels Standard 2 (RFS2). Virtually all biofuels producers in the United States must comply with the RFS2.

Biodiesel Definitions under the Renewable Fuel Standard

Under RFS2, biodiesel qualifies as a renewable fuel, as biomass-based diesel, and as an advanced biofuel. Here are the EPA definitions, straight from the Federal Register:

  • Renewable fuel – “fuel produced from renewable biomass and that is used to replace or reduce the quantity of fossil fuel present in a transportation fuel.” In general, to qualify under the RFS2, renewable fuel must show a 20% greenhouse gas reduction compared to the fossil fuel it displaces.
  • Advanced biofuel – “a renewable fuel other than ethanol derived from corn starch and for which lifecycle GHG (greenhouse gas) emissions are at least 50% less than the gasoline or diesel fuel it displaces.”
  • Biomass-based diesel—“includes both biodiesel (mono-alkyl esters) and non-ester renewable diesel (including cellulosic diesel).” The fuel must be made from renewable biomass; its lifecycle GHG emissions must be at least 50% less than the diesel fuel it displaces; and it cannot be co-processed with a petroleum feedstock.

If biodiesel does not meet one of the above definitions, it cannot be sold as a biofuel under the RFS2 program, no matter what “generation” it is claimed to be.


Knothe, Gerhard (2010). “Biodiesel and Renewable Diesel: A Comparison.” Progress in Energy and Combustion Science 36, pp. 364–373.

Regulation of Fuel and Fuel Additives: Changes to the Renewable Fuel Standard Program; Final Rule (March 26, 2010). Federal Register, Vol. 75, No. 58, 40 CFR Part 80. Accessed online at: http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2005-0161-2642

More Topics

Renewable Fuel Standard (RFS2) Basics for Biodiesel

For Additional Information

  • Forget Generational Biofuels — this is a blog post on the Biodiesel Discussion Forum at the University of Idaho’s Biodiesel Education Program. 2010.


Contributors to This Article


Jon Van Gerpen, Professor, Department of Biological and Agricultural Engineering, National Biodiesel Education Program, University of Idaho

Peer Reviewers:

Brian He, Associate Professor, Department of Biological and Agricultural Engineering, National Biodiesel Education Program, University of Idaho

Richard Nelson, Associate Professor, Center for Sustainable Energy, Kansas State University