Natural gas is composed primarily of methane, but it also contains small amounts of ethane, propane, butanes, pentanes and heavier hydrocarbons, collectively known as natural gas liquids. These liquids are separated and stored under pressure in tanks for shipment to factories, where they are used as raw materials to manufacture plastics and other products. Propane is also shipped to terminals that supply it for residential, industrial, vehicular, and other fuel uses.