Grey hydrogen
Hydrogen made from natural gas by steam methane reforming without carbon capture; the dominant and cheapest production route today.
Grey hydrogen accounts for most of the roughly 97–100 Mt of hydrogen produced worldwide each year (IEA Global Hydrogen Review 2024–2025). About two-thirds comes from natural gas reforming, with most of the rest from coal gasification (sometimes called brown or black hydrogen, mostly in China) and by-product hydrogen from refineries. Low-emission hydrogen remains below 1% of output.
In steam methane reforming, methane reacts with steam over a nickel catalyst at 700–1,000°C and 3–25 bar, followed by water-gas shift and pressure swing adsorption purification. The process needs about 165 MJ of gas per kg H2 (roughly 0.45 MMBtu), a conversion efficiency of 70–75% on LHV basis.
Coal gasification emits around 20 kg CO2/kg H2. Total hydrogen production emits roughly 900 Mt CO2 per year, comparable to the emissions of Germany and the UK combined.
Cost is mostly gas: at USD 3/MMBtu, grey hydrogen costs about USD 1/kg; at European gas prices of EUR 35/MWh, about EUR 2–2.5/kg before a carbon price. Main uses are oil refining (about 40%), ammonia for fertiliser (about a third) and methanol. Decarbonising these existing uses is the main near-term market for green and blue hydrogen.
Related terms
All terms →- Blue hydrogen
Hydrogen produced from natural gas by reforming, with most of the resulting CO2 captured and permanently stored.
- Green hydrogen
Hydrogen produced by splitting water in an electrolyser powered by renewable electricity, with near-zero direct CO2 emissions.
- Natural gas
A fossil fuel composed mainly of methane, used for power generation, industrial and residential heat, and as a chemical feedstock for hydrogen and ammonia.
- Ammonia as fuel
Use of ammonia (NH3), a carbon-free hydrogen carrier, as a fuel for ships, power plants and long-distance hydrogen transport.
- Carbon price
A cost applied per tonne of CO2e emitted, through a carbon tax or an emissions trading system, so that the climate damage of emissions enters market prices.