Coal Bed Methane (CBM) are Hydrocarbon gases formed in coal beds during the coal matter metamorphism process, i.e. changing of its structure, properties, and composition under exposure to temperature and pressure. Their main component is methane, whose concentration in the mixture reaches from 80 to 98 per cent.
During coal mining, it was important to extract methane from mines to prevent explosions. The United States was the first country that decided to turn it into a commercial enterprise. Ten per cent of gas is produced there today is using this technique. Most of the CBM is still wasted in traditional coal mining leading to large volumes of greenhouse gases.
Read more about CBM here http://www.worldcoal.org/coal/coal-seam-methane/coal-bed-methane/