Note on CO2 reductions: However, that is only part of the explanation. Most people don’t realize that almost all the material given off by any vehicle is CO2 and water—the regulated emissions are only a very small fraction of the gases coming out the back of a tailpipe. For example, if the particulates coming out of the back of an engines measure 0.1 grams, the CO2 would measure around 650 grams. So when you combine these factors, and the fact that biodiesel takes up CO2 when it is produced and provides a 78% life cycle reduction in CO2, that is why the CO2 reductions for biodiesel are so large.
Biodiesel provides a life cycle emissions reduction of 78% compared to petrodiesel. When carbon (with Molecular weight of 12) and hydrogen based fuel is burned (whether that is in an engine or otherwise) it combines with oxygen (molecular weight of 16) to make CO2 and water (H20). So, CO2 (weight 44) is more than 3 times the weight of carbon (12).