Coal, the most abundant of the fossil fuels and the second largest source of energy in the world, emits methane during extraction and distribution. Coal seams contain pockets of methane gas. Methane molecules also become attached through pressure and chemical attraction to the microscopic internal surfaces of coal itself. When the coal miners break open pockets in coal and coal bearing rocks, methane gas is released. The amount of methane released per unit of coal depends on the type of coal and how it is mined.
Some coal seams contain more methane per unit of coal than do others.
Not only is coal buried under high pressure deep in the earth able to hold more methane, but underground mining techniques allow additional methane to escape from both the coal that is not removed and from the coal-bearing rock. Fluxes in the methane emissions cycle are poorly known and, consequently, difficult to balance. These include emissions from fossil fuel and biomass burning. Fluxes in methane emissions have a minor bearing on its effect in the atmosphere. Its concentration of 1.7 ppmv compare to CO2 concentrations of 350 ppmv.