Today, there are two main ways to produce low- and zero-emissions hydrogen. The first is producing low-emissions hydrogen from fossil fuels with carbon capture. A common approach is hydrogen from natural gas via steam methane reforming (SMR) or autothermal reforming with carbon capture. The second is low- or zero-emissions hydrogen produced from water via electrolysis when using 100% renewable electricity.

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Geologic hydrogen is different. It is produced via natural water-rock reactions. The primary mechanism is when water reacts with iron-rich rock in a process called serpentinization. Unlike other types of hydrogen production, geologic hydrogen does not require external energy or water inputs and is therefore a primary energy resource.