Biomass is the total quantity of organic material produced. Methane is easy to transport and use. The systems for delivery are already largely in place. Ultimately, all come from CO 2 fixation by plants or solar energy. Cellulose is probably the most abundant organic compound.
Lignins are also very common.
When dried, straw or wood has only about half the energy content of oil. Sewage and animal wastes can also be fermented to product methane. Some of the limits are the cost and land area requirements to grow the crops. Many schemes of this type produce less energy than they consume. Destructive distillation of wood and many other plant materials produces methanol.