With gas prices soaring, people are looking for cheaper, renewable sources of fuel for their vehicles. Biodiesel fuel is used in diesel engines and is made from domestically available, renewable organic resources, such as vegetable oils and animal fats. Biodiesel burns cleaner (i.e. produces fewer emissions) than traditional petroleum diesel fuel and is biodegradable, making it an interesting alternative fuel option in terms of both environmental protection and U.S. energy independence. Biodiesel fuels most commonly available are really blends of biodiesel and petroleum diesel (B20, or 20% biodiesel, 80% petroleum diesel, for example). An American Society of Testing and Materials (ASTM) standard does exist for biodiesel (ASTM D6751). Based upon that standard, only pure (100%) biodiesel should be referred to as such. Any blend of biodiesel and petroleum diesel is properly referred to as "biodiesel blend." The intended audience for this publication is scientists and engineers interested in the technical aspects of biodiesel formulation and use. For more a more general overview of biodiesel, see the sites listed in the background section of this document.