Some facts:
It costs about 2.50/gallon for pure bio-diesel. There is a tax credit which reduces pure bio-diesel to $1.50/gallon.
Blends with regular diesel are indicated by a number indicating the amount of biodiesel. For instance, B2 is a 2% blend, B20 -20%, and B100 pure biodiesel.
Up to B5 -- requires no change to an existing diesel, increases the lubrication provided, and decreases harmful emmissions by about 10-20%.
B20 -- most commonly used fleet blend. Requires no changes to diesel engines built after 1994, with the above benefits by even more. This ratio (or higher) will provide clean air act EPACT credits as well.
B100 -- although diesel engines will run on this, it has some problems due to the acidity of the oil, and its tendancy to soften and rot rubber sealents over time. Modifications to feul systems (using different materials) allow this to operate with no problems, and a large number of benefits. This ratio does suffer from some issues in cold whether (like diesel #2), but is still very workable in things like generators, automobiles, etc.
For more info, see the
National BioDiesel Board