Biodiesel 

Biodiesel can be produced from the oil of crops including oilseed rape, sunflowers, and soybeans, as well as from waste cooking oils.  None of these oils should be used in engines un-processed as they leave damaging glycerine deposits.   Instead the oils are reacted with methanol to produce methyl esters - rape methyl ester (RME) is most common in the UK.  

Biodiesel is considered to be a renewable fuel as the crops usedto make the fuel take in carbon dioxide as they grow.   The main environmental advantage of Biodiesel is that is carbon neutral, so using 100% Biodiesel in your vehicle means you are not adding to the global warming crisis.  However, the environmental benefits at the point of use may not be as great as with some of the other fuels already discussed.