Natural gas is widely used to supply energy for domestic use and for industrial processes. It was formed millions of years ago by the same process that produced oil. Gas flows or is pumped out of boreholes, often mixed with oil and water. The gas is separated and passes through a refinery. Some of its constituents, such as propane and butane, are removed and liquefied so they can be pumped into cylinders and used as fuel. Liquefied gases held under pressure can be carried all around the world in specially constructed ships.
The remaining gas, which consists mostly of methane, is pumped along pipelines for domestic use. Methane has no smell, so a strong-smelling additive is used to make people aware of gas leaks.
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