The term biodiesel has no unambiguous definition. It stands for neat vegetable oils used as DF as well as neat methyl esters prepared from vegetable oils or animal fats and blends of conventional diesel fuel with vegetable oils or methyl esters. With increasing emphasis on the use of esters as DF, however, the term “biodiesel” increasingly refers to alkyl esters of vegetable oils and animal fats and not the oils or fats themselves. In an article on proposed ASTM standards, biodiesel was defined (9) as “the mono alkyl esters of long chain fatty acids derived from renewable lipid feedstock, such as vegetable oils or animal fats, for use in compression ignition (diesel) engines.” Nevertheless, clear distinction between these different vegetable oil-based or — derived alternative diesel fuels is necessary.

For use in the United States, the U. S. Department of Energy has stated (10), “that biodiesel is already covered in the statutory and proposed regulatory definitions of “alternative fuel” which refer to any “fuel, other than alcohol, that is derived from biological materials.” The Department, therefore, is considering amending the proposed definition of “alternative fuel” specifically to include neat biodiesel.” The definition of biodiesel was not extended to include biodiesel blends, with the Department of Energy stating that “the issue of including biodiesel mixtures or blends comprised of more than 20 percent biodiesel is currently under study. However, this subject is complex and will require significantly more data and information, and a separate, future rulemaking, before DOE can make a determination as to whether to include them in the definition of “alternative fuel.”