Hydrogen is a chemical element that is the simplest and most abundant element in the universe. On Earth, hydrogen is almost always found as part of another compound, such as water (H2O) or methane (CH4) . Hydrogen can be produced from a variety of resources, such as natural gas, nuclear power, biogas, and renewable power like solar and wind. The most common methods for producing hydrogen are steam-methane reforming and electrolysis. Steam-methane reforming accounts for nearly all commercially produced hydrogen in the United States. Electrolysis is a process that splits water with electricity to produce hydrogen. Other methods of hydrogen production include thermochemical processes, photolytic processes, and biological processes. However, it takes more energy to produce hydrogen than hydrogen provides when it is converted to useful energy.