Methane is a gas called natural gas. If you drive by a landfill, you might see a sort torch burning. The methane is being produced by the decomposing things under that landfill. Cows make methane. You can actually go out into a cow pasture, pick-up a cow pie (the waste, or poop) and light a match to it and it will burn nicely. That is the methane coming from the decomposing waste material.