Vast hydrogen reserves may lie underground — scientists assess the potential

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In the 1990s, Barbara Sherwood Lollar descended into the Kidd Creek mine in northern Ontario, which cuts more than three kilometers into the ancient root of North America. There her team of geochemists found water that had been confined underground for more than a billion years. This ancient brine turned out to be a habitat for living microbes that feed on the hydrogen produced in reactions between the water and the rock.

Decades later, Sherwood Lollar, who is a geochemist at the University of Toronto, revisited the team’s hydrogen data to see if there is enough of the gas in the mine to make it a useful source of zero-carbon fuel. “If we can set some smart minds into figuring out how to hook it up and use it, then we’ve got a win for this nascent economy,” she says.

While hydrogen fuel does show promise as a versatile power source, producing it typically generates lots of greenhouse-gas emissions and requires more energy than the gas contains. The ability to tap ready-made underground reservoirs—so-called “geologic hydrogen”—would change the equation.

A flurry of exploration efforts have launched to search for the stuff, which is produced underground when water molecules are split by chemical reactions with iron-rich rock or—as they are at Kidd Creek—by the radioactive decay of other elements. The hunt has spread all over the world and engaged dozens of startups, including the Australian firm HyTerra and the Bill Gates–backed company Koloma, which have both been poking around the US Midwest to reach ancient oceanic rocks associated with hydrogen production.

Researchers at the US Geological Survey have estimated that trillions of tons of H 2 are produced within Earth’s crust; if a small fraction of this could be recovered, it could meet global hydrogen demand for centuries. But the search so far has come up short. No one has yet reported finding a commercially viable reservoir of the gas, and public data on what has been found remains in short supply as companies jockey for position and seek to attract investment.

At Kidd Creek mine, Sherwood Lollar and her colleague Oliver Warr leveraged their long-term record of hydrogen to get a fresh read on the potential. By scrutinizing data they’d collected from 35 boreholes at the mine over more than a decade, they found that each one consistently released an average of eight kilograms of hydrogen per year. Extrapolating that finding to the more than 14,000 boreholes at Kidd Creek would mean that around 140 metric tons of the gas is flowing unused out of the mine’s vents each year.

This tally, published earlier this year in the journal PNAS , is not a world-changing amount, but Sherwood Lollar says that if all the hydrogen could be captured, it would offer at least a modest source of energy—perhaps enough to power a substantial portion of the mine’s operations. That would be a valuable local demonstration that geologic hydrogen really can be put to use, she says.

The results from Kidd Creek add to “the growing evidence that natural hydrogen generation and migration are genuine geological processes,” says Laurent Truche, a geochemist at the University of Grenoble Alpes in France. In 2024, his research team reported that at least 200 metric tons of the gas flow out of the Bulqizë chromium mine in Albania every year. “The remaining challenge is not proving that natural hydrogen exists, but proving that it can be produced economically and reliably at commercial scale,” Truche says.

Proof, however, doesn’t necessarily require striking the mother lode. Researchers and startups are also exploring the possibility of stimulating hydrogen production by injecting water, heat, or catalysts into the reactive rocks that naturally produce the gas. More than a dozen of these projects are funded by ARPA-E, which has established a goal of accelerating the hydrogen-producing reaction by a factor of 10,000—the rate at which, researchers estimate, stimulated H 2 production would be commercially viable.

An indication that this could work came earlier this year from the mountains of Oman, where a team drilled a one-­kilometer borehole and injected 50,000 cubic meters of water into the rock. When they opened the well several months later, gas was spewing out—and it was 90% hydrogen. “It’s bubbling with gas,” Jo Shannon, a geoscientist at the University of Southampton in the UK, told attendees of the European Geosciences Union conference in May. (Shannon declined to comment beyond what was presented.)

While Shannon said this was a promising sign, she was careful to add that a slew of unknowns remain. The most crucial question is a basic one: Is the hydrogen rising up out of the well made through stimulation, or had it been there all along?

James Dinneen is a science and environmental journalist from Colorado, based in New York City. He is working on a book about Earth’s deep interior.