Fuels, Combustion, and Energy, page 13 12. We mentioned previously that hydrogen gas was the most efficient of all fuels in terms of heat emitted per gram of fuel burned.
Gasoline is less efficient by nearly a factor of three, as the table at the right shows.
Fats, the main energy-storage system in animals, produce 9.5 kcal per gram upon combustion, and are almost as efficient in energy storage as gasoline. Glucose can store only 3.7 kcal per gram, so on a weight basis, starch is an inefficient material for storing energy.