In 1987, a worker lit a cigarette by a new water well near the village of Bourakebougou in Mali.
But as he did, an explosion reverberated inside the well. We now know this was due to previously undetected clouds of flammable hydrogen wafting from a gas reservoir beneath the hole.
Bourakebougou’s well is the world’s first and only productive hydrogen well. Mixed with oxygen in fuel cells, hydrogen — the smallest and simplest molecule in existence — can generate electricity without greenhouse gas emissions and with only heat and water as byproducts. This makes hydrogen a clean source of energy, and demand for it is expected to rise fivefold by 2050 to produce microelectronics, supply industry, and power vehicles and buildings.
Resource exploration companies are now rushing to find reservoirs of natural hydrogen, also known as “gold” hydrogen. To help them, scientists have identified the key “ingredients” needed to form such accumulations. And thanks to this knowledge, techniques to boost or mimic natural hydrogen generation that were once considered impracticable are gaining traction, experts told Live Science.
“We just keep finding more and more the more we start looking for it,” Geoffrey Ellis, a petroleum geochemist with the U.S. Geological Survey, told Live Science.
Paradigm shift
Hydrogen is a source of energy, but it is also a critical component of fertilizer, refined oil and rocket fuel. Industry produces almost all of its hydrogen by heating natural gas with steam to form a mixture of hydrogen and carbon monoxide from which hydrogen can be extracted.
This method makes “gray” hydrogen, and it pumps about 1 billion tons (920 million metric tons) of carbon dioxide into the atmosphere every year — equivalent to 2.4% of global annual emissions. In theory, renewable energies can replace natural gas to generate “green” hydrogen, while “blue” hydrogen is made from fossil fuels but with carbon capture, meaning carbon doesn’t enter the atmosphere. But these collectively make up a tiny fraction of hydrogen production worldwide.
“Hydrogen is a clean source of energy, but how you get your hydrogen is critical,” Chris Ballentine, a professor of geochemistry at the University of Oxford, told Live Science.
However, a new source of hydrogen could slash the industry’s carbon footprint, as it turns out that huge quantities of hydrogen can accumulate belowground. Scientists have long known that rocks in Earth’s crust produce hydrogen, but experts previously concluded that the gas couldn’t collect in reservoirs because only tiny concentrations of it were being found in oil and gas wells.
The discovery in Mali toppled that theory. Researchers realized that the places where companies drill for oil and gas are not the best places to find hydrogen.
Massive reservoirs, waiting to be found
The Mali discovery has kicked off a worldwide hunt for hydrogen reservoirs. But before geologists initiate costly exploration projects, they need a sense of just how much hydrogen might be lurking underground.
New estimates suggest it’s a staggering amount. Earth’s continental crust has produced enough hydrogen over the past 1 billion years to meet society’s current energy needs for 170,000 years, a recent review by Ballentine and his colleagues found. Though much of this hydrogen has escaped into the atmosphere, the figure is “a starting point for realizing that the hydrogen generation in the crust is significant,” Ballentine said.
Other estimates double the figure in the Ballentine paper. Ophiolites are chunks of oceanic crust that have been thrust onto the continental crust, and some estimates suggest these ocean-crust remnants may produce as much hydrogen as the continental crust does, Ballentine said.
But how much of this hydrogen is left in Earth’s crust? In 2024, Ellis and his colleagues calculated that the planet holds 6.2 trillion tons (5.6 trillion metric tons) of hydrogen, or about 26 times the amount of oil known to be left in the ground. Where these hydrogen stocks are located is largely unknown. Most are likely too deep or too far offshore to be accessed, and some reservoirs might be too small to be worth extracting — but the researchers emphasized that just 2% of the total hydrogen could supplant our current fossil fuels for 200 years.
“The potential that’s down there is quite, quite large,” Ellis said. What’s more, natural hydrogen, unlike the type made via industrial processes, comes with built-in storage because it sits in Earth’s crust. It also has a much smaller carbon footprint than manufactured hydrogen, with emissions coming only from extraction, Ellis said.
The ingredients
In January 2025, Ellis and his colleagues published a map showing where hydrogen reservoirs might exist in the lower 48 U.S. states. The researchers used gravity and magnetic signal data to estimate the composition of rocks throughout Earth’s crust and determine where hydrogen may have migrated underground.
“This was the first time that anyone had attempted to do this type of mapping exercise,” Ellis said.
The researchers estimated the likelihood of productive hydrogen reservoirs, known as prospectivity, based on six geological requirements that make and trap hydrogen in Earth’s crust. On the map, prospectivity ranges from 0 to 1, with 0 meaning there is likely no hydrogen and 1 indicating hydrogen is very likely present.
To form a hydrogen reservoir, the first and second requirements are that a region must have abundant groundwater and hydrogen-producing rocks. The water requirement limits hydrogen production to the top 10 miles (16 kilometers) of the crust, Oliver Warr, an assistant professor of geochemistry at the University of Ottawa, told Live Science.
The best hydrogen-producing rocks are iron-rich rocks, which generate hydrogen through “hydration reactions,” where water reacts with the rocks. Other good sources of hydrogen are uranium- and thorium-rich rocks, which produce alpha particles as the radioactive elements decay. These alpha particles can then split water into oxygen and hydrogen — a process known as radiolysis, Warr said.
Iron-rich rocks include basalt and gabbro. Earth’s mantle, the layer beneath the crust, heats groundwater, producing steam that reacts with iron and generates hydrogen. Uranium- and thorium-rich rocks include granites, and these can trigger the radiolysis of water.
The third requirement is that the source rocks be very, very hot — between 480 and 570 degrees Fahrenheit (250 to 300 degrees Celsius), which guarantees rapid rates of reaction, Ellis said.
Fourth, the region must have reservoir rocks that can hold the hydrogen after it is produced and migrates through the crust. Reservoir rocks are typically porous sandstones, but other types of rock can also work if they are highly fragmented, Ellis said.
The fifth criterion to form a hydrogen reservoir is an impermeable “seal” to trap the gas inside the reservoir. “A thing like a shale, or maybe a salt, would be really ideal to be sitting on top of that porous rock,” Ellis said. Crucially, the seal must exist when the hydrogen is produced, or else the gas escapes into the atmosphere, he said.
The sixth and final condition is that there must be minimal microbial activity where hydrogen is generated and accumulates, because microbes consume hydrogen, Warr said.
These six conditions, or ingredients, occur across all continents, Ballentine said. Currently, hydrogen companies are drilling exploratory wells mostly on the Midcontinent Rift — where North America started, but ultimately failed, to split apart 1 billion years ago — which is abundant in iron-rich rocks.
Looking ahead
Researchers are also investigating hydrogen deposits in Oman, where there are ophiolites. University of Colorado geologists are running a pilot project in the country to test the feasibility of “stimulated hydrogen” production, Ellis said.
Stimulated hydrogen production takes inspiration from what scientists have learned about the geology that makes and accumulates hydrogen. It involves injecting water into Earth’s crust to kick-start either hydration reactions or radiolysis.
One year ago, people in the hydrogen industry were skeptical that stimulated hydrogen production would ever materialize, Ellis said. But now, “I’ve seen a big shift,” he said.
If we can find natural hydrogen and extract it, the gas could reduce emissions across a wide range of sectors. For example, abundant hydrogen is found in mines, because this is where humans drill deepest into the crust, so the gas could power mining operations, Warr said.
Natural hydrogen could also slash emissions from industries such as fertilizer manufacturing. “If we can replace hydrogen generated from hydrocarbons with clean hydrogen, then we can very rapidly make a massive difference,” Ballentine said.
Natural hydrogen won’t solve the climate crisis, but it can mitigate some of the risks. “It needs to be one of many strategies,” Warr said. “We just need to understand the true potential and how it can best be capitalized on.”
Some of the key considerations for companies are whether the benefits of developing natural hydrogen reservoirs when we find them would justify the cost of building production plants on-site, or shipping the gas to the industries that need it.
“If you’re remote and you find a really big gas field, it still may not be worthwhile producing it, because the costs of getting hydrogen to market are too great,” Ballentine said. “There’s a trade-off.”
But overall, experts are optimistic. “There have been, I think, over a dozen wells that have been drilled now in the U.S.,” Ellis said. “They’ve found a lot of hydrogen.”
