The earth has a huge stock biomass covering wide regions including forests and the ocean. The total biomass of the world is 1,800 billion tons on the ground and 4 billion tons in the ocean, and a comparative amount of biomass exists in the soil. The total biomass on the ground is 33,000 EJ on the energy basis, which corresponds to 80 times or more of the annual energy consumption of the world.

However, some part of the biomass is used as food by living things including humans, and also for uses other than foods, which are necessary for the human living. Therefore, it is important to estimate quantity of biomass resources, which can be used for energy source.