Biogas is plentiful and is available from sources such as landfills, wastewater treatment facilities, and animal and agricultural waste. If fully utilized, the yield from existing organic waste streams could satisfy about 20 percent of current natural gas use. Biogas feedstock may also soon be farmed economically. Work is already underway to develop low-cost dedicated energy crops such as algae and other plant species that can be grown on marginal land to serve as a source of biogas production. Future energy crops could make the potential availability virtually unlimited.