Can they? I know in America we use corn ethanol in our gas and its common knowledge (read: I've heard it a million times and didn't look it up anytime in the past decade) that it uses more petroleum energy to obtain than you get out. Add in that our food supply is about to get worse because of climate change thats a concern.

Biofuel is great in cases like burning kudzu (fast growing invasive plant responsible for some impressive pictures) for fuel or in cases where weight to energy is vital like aviation. But there's a limit on how much can be used at any time