Natural gas

Liquified natural gas tankers store cryogenically cooled gas, as a liquid, in heavily insulated tanks

Natural gas is a form of petroleum.

With the exception tar sands, and pitch seeps, petroleum is found deep underground, trapped in a layer or layers of porous rock, overlain by a dome of impervious non-porous rock. Each hydrocarbon found in petroleum has a different melting point and boiling point, depending on the number of atoms in a molecule. The four lightest hydrocarbons, methane, ethane, propane and butane have such low boiling points they are gaseous at room temperature. So some of these components of petroleum fractionate out, and float on the top of underground deposits.

In recent decades it has been recognized that natural gas is less polluting to burn than petroleum products composed of heavier hydrocarbons.

Natural gas is, however, harder to transport and store than petroleum products that are liquid at room temperature.