The use of biological agents to convert relatively diffuse and inconvenient to use sources of energy, e.g., biomass and sunlight, into more energy dense and convenient to use fuels, e.g., methane, ethanol, butanol, biodiesel and hydrogen, constitutes fuel biotechnology.
Biomass is the total cellular dry weight or organic material produced by an organism (usually from CO2 and sunlight), while biologically produced fuels are usually called biofuels. In general, biofuels are aimed for use in transport as a substitute for the nonrenewable and rapidly declining fossil fuels derived from petroleum.
Initially, biomass was the only source of energy available to and used by man. But the development of fossil fuels (coal and oil) rapidly reduced the use of biomass as energy source, especially in the developed countries, which an also the largest (per capita as well as total) users of energy
Biomass still contributes a large part (74%) of the energy needs of developing countries, while only about 2% of energy used by developed countries is directly obtained from biomass.
More recently, economic and industrial developments in the developing countries has contributed to an enhanced use of fossil fuels. These considerations have forced man to seriously consider the option of biofuels as a replacement for fossil fuels.