Bacteria Fuel

PRO: 50% more energy per gallon than ethanol; no need for refining
CON: Hasn’t been tried on a large scale yet; potential regulatory issues

Algae Biodiesel

PRO: Cheaper and more efficient to produce than soy biodiesel or ethanol
CON: Delicate algae are hard to keep alive and churning oil by the billions

Ethanol

PRO: Made from common crops such as corn; proven and existing technology
CON: Less energy than biodiesel; needs pricey, eco-unfriendly refining

Soy Biodiesel

PRO: Made from soybean oil, which is already widely made; nontoxic
CON: Costlier than bacteria or algae fuel; turns solid at low temperatures