Bioethanol is a fuel made from plants, and it stores less energy per volume than petroleum-based fuels. When you burn it alongside gasoline, diesel, and kerosene — holding a test tube of water above each flame — bioethanol produces the smallest temperature rise of the four. Gasoline heats the water the most, though it burns out fastest at just 41 seconds. Diesel takes the opposite approach: it burns the longest at 89 seconds but heats the water less than gasoline does.