A nighttime photo shows fire spurting from rocks.
Credit: Getty Images
Hydrogen from geological formations makes up about 10% of the flammable gases that form the Yanartaş flames near Cirali, Türkiye. The fires are said to have been burning for thousands of years and may be the flaming rocks mentioned in the myth of the Chimera.
In brief
Geological resources may be able to provide billions—or even trillions—of metric tons of clean hydrogen, according to estimates from US government researchers. By tapping into existing hydrogen accumulations and stimulating underground rocks to make more of the electron-rich gas, a new crop of energy entrepreneurs think they can put low-carbon hydrogen on the market for as little as $1 per kilogram. The concept is proven at just one site today. But if it works as well as its advocates and investors say, it could be a major win in the fight against climate change.
Hydrogen is a popular molecule right now. Billions of dollars are flowing from investors and governments into projects to make more hydrogen and use it to decarbonize both industry and transportation. But what’s often lost in the discussion is that hydrogen is really an energy transfer medium, not an energy source.
The hydrogen available today is made in processes that are powered by renewable energy or, more often, fossil fuels. Molecular hydrogen as it is used and traded now is no more or less sustainable than the energy used to create it.
Except, that is, in Bourakebougou, a small town in southwestern Mali. There, almost 40 years ago, engineers drilling for water tapped instead into a natural underground reservoir of hydrogen gas. What they saw—a dry well emitting wind instead of water—was at first a disappointment.
Then, according to local lore, it became a catastrophe. A worker smoking a cigarette accidentally ignited the gas stream, creating a huge plume of smokeless fire that burned for weeks before workers were able to extinguish it. Tests showed it wasn’t natural gas, so they capped the borehole and walked away.
The idea of tapping such geological hydrogen had been confined to academic circles until around 2012, when Aliou Diallo, a Malian businessman, hired a mobile analytical laboratory to characterize the gas at the site. Diallo had purchased oil and gas exploration rights in the area after hearing about the flaming well.
Geologists who’ve drilled wells before will have to admit that we’ve drilled a lot of dry holes.
Michael Hession, cofounder, Helios Aragon
The mobile lab found 98% pure hydrogen. For Bourakebougou, the discovery brought the fuel needed to generate reliable electricity, at first via a modified car engine and later through purpose-built equipment. It also changed Diallo’s business, which is now called Hydroma and is focused on geological hydrogen.
Diallo is part of a growing crowd of geochemists, entrepreneurs, and investors who see opportunities worldwide to develop geological hydrogen as a primary energy source with little impact on the climate, unlike carbon-containing fossil fuels. Companies are drilling about 200 exploration wells across the globe, mostly in secret, according to industry sources. But so far, Bourakebougou is the only one to produce anything of any economic value, and experts don’t know if geological hydrogen will remain a useful curiosity or launch a new energy economy.
Clean energy under our feet
Douglas Wicks, a program director exploring geological hydrogen for the US Department of Energy’s Advanced Research Projects Agency–Energy (ARPA‑E), says one reason there aren’t more productive projects is that no one has been looking for the gas underground until recently. “The Earth has been producing hydrogen at large volumes for all of history,” he said during a panel discussion on geological hydrogen at Climate Week NYC in September. “We just chose as humankind not to really pay attention.”
The hydrogen found underground gets there by a handful of chemical mechanisms. In the most important one, rock rich in iron(II) and magnesium comes into contact with water at elevated temperature and pressure. If conditions are right, electrons transfer from the iron to the water, resulting in molecular hydrogen, iron(III) oxides, and silica compounds.
Geochemists call the process serpentinization because it produces serpentine minerals such as antigorite, lizardite, and chrysotile, which often have a scaly appearance. The best minerals for serpentinization are mafic and ultramafic rocks, which feature magnesium and chromium alongside the iron and silicon. Manganese, cobalt, and nickel are often present in these rocks as well.
Radioactive decay of uranium, thorium, or other elements can also split water and form hydrogen, albeit much more slowly than serpentinization. The resulting hydrogen accumulates in porous rock such as sandstone that lies underneath impermeable layers made of rock such as shale or salt. Researchers also think Earth’s core and mantle shed primordial hydrogen into the planet’s outer layers through tectonic faults (Annu. Rev. Earth Planet. Sci. 2001, DOI: 10.1146/annurev.earth.29.1.365)
The chemistry and geology get complicated quickly, which is why the nascent industry is excited about a new set of studies from the US Geological Survey (USGS). The first looks at the mechanisms by which hydrogen is created, consumed, and released deep underground to estimate the quantity that is made each year and how much might be trapped in reservoirs like the one in Bourakebougou (Sci. Adv. 2024, DOI: 10.1126 /sciadv.ado0955).
The researchers, led by USGS staffers Sarah E. Gelman and Geoffrey S. Ellis, calculate that about 5.6 trillion metric tons (t) are trapped in geological formations around the world and that another 15 million–31 million t emerge every year. Ellis testified about the results before the US Congress in February 2024.
The researchers emphasize that most of the hydrogen isn’t economically accessible, but because the volumes are so huge, harvesting even a small percentage could make a big impact on climate change, they say. “We calculate the energy content of this estimated recoverable amount of hydrogen to be roughly twice the amount of energy in all the proven natural gas reserves on Earth,” they write in the paper.
In a second study, the USGS explores likely geological hydrogen opportunities in the 48 contiguous US states. Ellis and team looked for areas with formations capable of releasing or making hydrogen and overlaid that data with information about rock layers capable of trapping gases as they rise from deep underground.
The result is a map showing areas with potential that stretch from the Appalachian Mountains to the Rockies, along with a strip along the West Coast. It is accompanied by a paper detailing the researchers’ methods (U.S. Geol. Surv. Prof. Pap. 2025, DOI: 10.3133/pp1900).
The USGS work has bolstered the credibility of underground hydrogen as a primary energy source and has featured heavily in public and private discussions since it came out. Every chair was full at the Climate Week NYC event, and more people were packed along the walls and into the hallway. The Activate Fellowship, a nonprofit science entrepreneurship program that cohosted the event with ARPA-E, had already changed the venue twice as more and more people signed up.
The crowd was a potent mix of the kinds of people you need to start an industry. There were funders such as venture capitalists, banks, entrepreneurship programs, nonprofits, and government grant officers; researchers from academia and the federal government; and technically oriented executives from start-ups and multinational corporations.
And people are doing more than just talking. In August, the mining giant Fortescue paid $21.9 million for a 40% stake in HyTerra, a start-up that’s developing a pair of geological hydrogen sites in the US Midwest. HyTerra estimates that its main project, in northeastern Kansas, could yield 250,000 t of hydrogen along with 2,200 t of helium, which accumulates underground under similar conditions. Earlier last year, the biggest geological hydrogen player, Koloma, raised $247 million in series B funding from investors that included Breakthrough Energy Ventures and Amazon.
It’s hard to identify a full roster of geological hydrogen companies because many are keeping quiet while they lock down their prospects. Panelists at the Climate Week NYC event guessed that about 50 firms are gathering data, negotiating exploration rights, and drilling test wells.
“I would estimate that half of what’s invested into this industry is in Koloma,” said Morten Stahl, a partner at the investment fund Natural Hydrogen Ventures.
Exploring for hydrogen
At the Climate Week NYC event, Wicks divided the field into two main groups: those looking for pockets of existing hydrogen and those aiming to stimulate serpentinization by injecting water into iron-rich rocks.
“There are wildcatters going around looking for these natural accumulations of hydrogen, coming in and saying, ‘Can we just poke a hole into it, put a straw and start sucking out hydrogen like it’s natural gas?’ ” Wicks said. “The other thing to keep in mind, though, is that hydrogen forms at a speed which is in human time scales. Unlike natural gas that takes millennia to be produced, we can actually stimulate and accelerate the formation of hydrogen.”
Stimulating geological hydrogen production means turning rocks rich in iron(II) into chemical reactors buried deep underground, according to Iwnetim “Tim” Abate, a professor of materials science and engineering at the Massachusetts Institute of Technology. Abate, who was one of C&EN’s Talented 12 in 2023, was awarded a federal research grant to study stimulated hydrogen production. But his bigger bet right now is on using that geological reactor to make ammonia.
Abate’s group published a paper in Joule in January describing the reaction of olivine, a common iron(II) mineral, with aqueous nitrate (2025, DOI: 10.1016/j .joule.2024.12.006). The bench-scale system used in the paper gives high yields of ammonia. Abate and his team combined those results with estimates of iron(II) in Earth’s crust to conclude that scaled-up versions could produce 235 million t of ammonia per year for millions of years at a cost of $0.46–$0.55 per kilogram. If efforts to use N2 as the nitrogen source work, the cost could drop as low as $0.30 per kilogram.
Conventional ammonia costs about $0.40 per kilogram, and global consumption sits at around 150 million t per year, according to the data provider Statista. The paper estimates that the group’s “abate cycle” would have carbon dioxide emissions just 3% of that of conventional ammonia production.
Making ammonia instead of hydrogen makes sense because hydrogen gas is hard to handle; most low-carbon hydrogen projects plan to convert the gas to ammonia, methanol, or some other liquid. And one of the highest-volume uses of any kind of hydrogen today is the Haber-Bosch synthesis of ammonia.
If geological ammonia sounds like a business plan, that’s because it is. In addition to his professorship at MIT, Abate is the cofounder of Addis Energy, a start-up that aims to commercialize the ammonia technology. Addis came out of stealth in January and has raised $8.75 million from venture capital firms, MIT, and ARPA-E.
Be they used for creating ammonia, hydrogen, or even some other energetic molecule, the electrons waiting underground in iron(II) minerals offer opportunity. “The chemical potential that we’re trying to unleash with the ARPA-E program is measured in the hundreds of trillions of tons, if not quadrillions of tons of hydrogen,” Wicks said. “There’s chemical potential beneath our feet, if the engineers can figure out how to control it and harness it.”
Zainub Noor, director for technology and innovation at the venture capital arm of the oilfield services firm Halliburton, said at the Climate Week NYC event that geological hydrogen projects mostly use available technologies that are well understood from decades of use to extract natural gas.
That said, prospecting for hydrogen and fossil fuel gases are not entirely the same, Noor said. Methane and ethane have strong infrared absorbance peaks that make them simple to detect spectroscopically, whereas hydrogen requires more-complex and specialized sensors. Hydrogen also tends to accumulate in rock formations that are physically harder than, but not as deep as, those that contain natural gas.
Borrowing from an existing industry is a big advantage that Noor expects will catapult geological hydrogen from an unproven idea into a commercial force much faster than is possible for clean energy technologies that must be built from scratch. “This will be the least expensive source of hydrogen as soon as technical feasibility is proven,” she said. “We strongly believe that this will be one of the biggest breakthroughs of this era.”
Building out an industry
It all sounds promising. And it’s almost completely unproven, so far. The risks of geological hydrogen were the main subject of conversation at another packed room, this one 8 days later in Copenhagen during the World Hydrogen Week conference.
“It’s all about asymmetric risk in our life. We’re always looking for an investment that has greater upside than downside,” said Owain Jackson, CEO of the geological hydrogen developer H2Au, which is developing sites in South Africa and the US Midwest. “There is a macro risk around natural hydrogen that is coming down daily, and we’ll have some big shifts ahead. That risk profile at the moment is very much a factor of it being new.”
Jackson, a geologist who worked for decades in oil and gas exploration, said firms like his should adopt both the equipment and the business practices of the fossil fuel industry. “Every dollar that is committed in exploration must always be committed against reducing risk along the way. It’s a staged investment, made parallel to risk. There’s no big, massive moment where you put all your money on the table and it’s either gone or not the next day.”
Michael Hession, cofounder of the Spanish geological hydrogen start-up Helios Aragon, also came from the fossil fuel world. “Geologists who’ve drilled wells before will have to admit that we’ve drilled a lot of dry holes,” he said at World Hydrogen Week. For oil and gas, about 1 in 10 pays off. “Is it worth drilling that hole at a risk of 1 in 10? And the answer generally is, these companies that have gotten very big and made a lot of money have done so by understanding that risk.”
Overall, the risk profile is attractive compared with those of other ways to get low-carbon hydrogen, Stahl, the investor, said in Copenhagen. “I totally accept the risk of drilling. For me, it’s just a numbers game. Maybe if we drill a well, we won’t find anything. But if we find something, it could be really, really cheap. Game-changingly cheap. So cheap that it’ll actually be bought by someone without subsidies,” he said.
Industry analysts project that geological hydrogen, if it works, will cost about $1 per kilogram. That’s much cheaper than making low-carbon hydrogen by splitting water with renewable electricity or by reforming methane and capturing the CO2 by-product; hydrogen made these ways runs an estimated $7 and $3 per kilogram today, respectively. In fact, $1 per kilogram is cheaper than most unabated fossil hydrogen. It’s also the target set for 2031 in the DOE’s marquee hydrogen-focused Earthshot.
Regardless of the source of the gas, the clean hydrogen market has a chicken-and-egg dilemma right now in which suppliers don’t want to scale up until they’re sure they’ll have customers, and companies that could adopt their hydrogen don’t want to make the investment until supplies are cheap and plentiful. And so the business is at an impasse.
People in all corners of the hydrogen industry are excited about geological hydrogen because it could break the impasse and get enough of the low-carbon energy source into the market that customers can build factories and demand can start growing.
It’s also possible, if the high end of the USGS estimates bear out, that geological hydrogen could render other types of low-carbon hydrogen obsolete, according to Bo Sears, CEO of Helix Exploration. Helix is mainly interested in geological helium, but at a site in Montana it found hydrogen as well and sees the potential to stimulate the rocks to make more.
Other ways to get low-carbon hydrogen are too dirty, too expensive, or both, Sears told C&EN, and production costs won’t come down in time to put hydrogen at the center of an energy transition that can stave off climate change. “The last remaining hope is geological hydrogen, which would certainly get us to our goal of 1 kg for $1 in 1 decade,” he said. “If it works.”