Biodiesel is delivered either as 100% or in biodiesel/petrodiesel blends.
- 100% biodiesel is referred to as B100, while
- 20% biodiesel is labeled B20
- 5% biodiesel is labeled B5
- 2% biodiesel is labeled B2
Most of the biodiesel available today comes from soybeans, which can lead environmentally conscious people to argue that using food as a machine fuel contributes to world hunger. However there are lots of schemes out there to create biodiesel from non-food sources- algae, fungi, and, my favorite, coffee grounds.
NYT article on making biodiesel from coffee grounds:
http://www.nytimes.com/2008/12/16/science/16objava.html
Food Chemistry article on biodiesel production from coffee grounds:
http://pubs.acs.org/doi/abs/10.1021/jf802487s