Anonymous

Many are already.

Anonymous

The processing costs for the oil, and possible refitting of the truck fleet, may make the plan unprofitable when compared with other oils.

Anonymous

It's against the law in most countries including the US.

Anonymous

Organic chemistry. Some are too reactive or saturated or what have you. Their chemical structures and properties determine all of this.

Anonymous

A lot depends on their melting point. Olive oil, for example, turns solid at about 60º so it would not work at colder temperatures.

Anonymous

Cost and availability and there is moral uncertainty about turning food into fuel when there are starving people in the world.