Biodiesel is a clean burning fuel produced from domestic and renewable plant and animal oils and fats.  It can be used as an alternative to standard diesel fuel or added in different percentages.  The fuel contains no petroleum and is renewable, non-toxic, and can be replenished through farming and recycling.
Biodiesel can be used in diesel engines ranging from its pure form to a 20% mixture with standard diesel fuel.  It is produced through a chemical process that splits the plant or animal fat into two forms esters and glycerol using an alcohol and a catalyst.  The esters are the biodiesel.   Biodiesel has many benefits.  It contains few emissions than standard diesel, it derives from a renewable source, it can be used in almost any diesel engine, and it acts as an engine lubricant.

http://auto.howstuffworks.com/biodiesel3.htm  information retrieveon 7/19/2007
http://www.biodiesel.com/whybiodiesel.htm  information retrieveon 7/19/2007
http://www.wisconsinbiofuels.com Photo of biodiesel plant.