While hydrogen is the most abundant element in the universe. Not all are created equal, with trade-offs on cost and environmental impact.

“Gray” hydrogen accounts for most of the hydrogen produced in the U.S. today. It comes from natural gas and releases carbon emissions during production and processing.

Less common options include brown hydrogen, which comes from coal, and pink hydrogen, which uses nuclear power to split hydrogen molecules from water.

Blue hydrogen is produced the same way as gray hydrogen. But producers capture and store the carbon emissions, making it a greener option. It’s still not green enough for most climate activists.

Green hydrogen uses solar and winds energy to power the process of extracting hydrogen from water. Because it doesn’t release any carbon in the process, it’s the gold standard for hydrogen production.