Natural gas is a mixture of gases. It consists mainly of hydrocarbons. The main component is methane, which is a greenhouse gas. Natural gas is a natural resource, often found in the ground, either alone or together with petroleum. Landfills and natural processes produce a little methane. Usually it is transported to users in a pipeline.
Most natural gas is burnt as a fuel to produce energy. It burns with a blue flame. Like other flames, this can cause pollution with nitrogen oxides.