Hydrogen is the lightest of all elements and constitutes 90 percent of the known universe. The gas may be obtained by means of a steam-reformer from steam, natural gas or other light hydrocarbons. Refineries and electrolytic processes employed in chlorine chemistry also generate hydrogen-rich gases from which the hydrogen can be recovered. Liquid hydrogen is manufactured by liquefaction at -253°C and is transported in its liquid state, thus reducing transport costs.