Biodiesel is a type of fuel prepared by modifying vegetable oil. In Brazil, castor beans are the best stuff to make biodiesel out of, because they're easier to plant and cost less than soybeans, sunflower seeds or other seeds. In Germany biodiesel is, for the most part, produced from rapeseeds. Biodiesel is commercially available in most oilseed-producing states in the US. In Thailand, the raw material will most likely come from palm oil, coconut oil, Jatropha curcas, and tallow. Biofuel prepared from biomass is different since it is not transesterified oil.

Biodiesel refers to a non-petroleum-based diesel fuel consisting of long chain alkyl (methyl, propyl or ethyl) esters, made by transesterification of vegetable oil or animal fat (tallow), which can be used (alone, or blended with conventional petrodiesel) in unmodified diesel-engine vehicles. Biodiesel is distinguished from the straight vegetable oil (SVO) (sometimes referred to as "waste vegetable oil", "WVO", "used vegetable oil", "UVO", "pure plant oil", "PPO") used (alone, or blended) as fuels in some converted diesel vehicles.

"Biodiesel" is standardized as mono-alkyl ester and other kinds of diesel-grade fuels of biological origin are not included.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)

For More Information: Make Your Own Biodiesel - Experiments and Background Information