Green hydrogen is commonly produced using renewable energy to electrolyse water into hydrogen and oxygen.

Blue hydrogen is the low-carbon version of grey, black or brown where CO₂ is captured.

Pink/purple hydrogen is produced from a low-carbon nuclear power source and is likely to play a significant longer-term role.

Turquoise hydrogen refers to emerging processes, such as pyrolysis of methane, where solid carbon is removed, not CO₂.

Yellow hydrogen is produced from the current grid through electrolysers using renewable or conventional power.

Grey hydrogen, the current production technology, involves reforming of hydrocarbon gas in a CO₂-intensive process.

Black and brown hydrogen are produced by reforming or gasifying oil and coal, another CO₂-intensive process.

White hydrogen is recovered from geological sources and it could make a small contribution.