It is very easy to obtain, so it is a good use for an early supply of energy. Any form of plant life can be turned into a bio fuel. Simple life such as seeds will produce 2 bio fuel, whereas more complex life such as pumpkins, melons, or potatoes will produce 4 bio fuel. To actually create it simply take your plant life and stick it into a powered Crusher. As of 9.3.4, melons and pumpkins are usable as plant matter, and will convert to 4 Bio-Fuel each. This means that melons are now the most efficient plant matter in crop to fuel ratio, and appear to be the most efficient plant overall.