Beneath the surface: What you need to know about geologic hydrogen
Hydrogen has long played a vital role in the industrial landscape, from fertilizer production to petroleum refining. It will remain essential in a decarbonizing economy, where it is uniquely positioned to replace today’s carbon-intensive hydrogen use in “no-regrets” sectors such as hard-to-electrify industries, fertilizer production, petroleum refining, maritime shipping, heavy-duty trucking, and aviation.
As momentum builds behind the push for cleaner hydrogen, most of the attention has gone to technologies like electrolytic hydrogen powered by renewable energy, or fossil-based hydrogen with carbon capture. But another, lesser-known option is beginning to make its way into the conversation: geologic hydrogen, sometimes referred to as “natural,” “white,” or “gold” hydrogen. Formed underground through natural processes in the earth’s crust, this hydrogen source theoretically has the potential to offer an affordable, low-emissions complement to other low-carbon hydrogen pathways.
Though still in its infancy, geologic hydrogen is quickly capturing the interest of researchers, policymakers, energy companies, and clean energy advocates. With exploration underway in the U.S., Europe, and beyond, it’s important to take a clear-eyed look at both its potential and the uncertainties. This piece offers a snapshot of what geologic hydrogen is, what we know so far, and what we still need to learn.
What is geologic hydrogen?
Geologic hydrogen refers to molecular hydrogen (H₂) that forms naturally beneath the earth’s surface. Unlike most hydrogen today, which must be manufactured through energy-intensive processes, geologic hydrogen is produced through natural reactions such as serpentinization and radiolysis.
- Serpentinization occurs when water interacts with iron-rich rocks like peridotite, splitting water molecules and releasing hydrogen as a byproduct. This process is common in tectonically active regions and is influenced by temperature and pressure. Higher temperatures (200–400 °C) and elevated pressures usually accelerate reaction rates and thus result in higher hydrogen yields.
- Radiolysis occurs when radiation from naturally occurring radioactive elements breaks apart water molecules trapped in rock, releasing hydrogen. This process is slower and lower yielding than serpentinization but can occur across a wider range of geological settings.
- Other processes, though less common, such as microbial activity and the breakdown of organic matter, can also produce hydrogen in sedimentary basins
.where microbes or heat gradually release hydrogen from buried carbon-rich materials.
Extraction of naturally formed geologic hydrogen from underground reservoirs is by far the most technologically mature method of production. However, researchers are also actively exploring other engineered methods where geologic hydrogen can be “manufactured” in more controlled environments:
- Stimulated Accumulation: In cases where hydrogen is present in geologic formations but not freely flowing, techniques like hydraulic fracturing or electrical stimulation can help release it from the rock and make subsequent extraction feasible.
- Stimulated Generation: Hydrogen can also be produced underground by injecting water into reactive iron-rich rocks to trigger hydrogen-generating reactions like serpentinization.
Why are people excited about geologic hydrogen?
By late 2023, more than 50 companies globally were investing in geologic hydrogen exploration, according to American Gas Association’s estimates. This growing interest is likely driven by several of geologic hydrogen’s unique advantages compared with other low-carbon energy sources:
- Theoretically low carbon footprint. Unlike hydrogen made from fossil fuels, generating geologic hydrogen requires no feedstock. Its carbon intensity comes primarily from the extraction process. Existing studies suggest it could have near-zero carbon intensity, particularly when not co-produced with methane. For example, hydrogen with 85% purity and minimal methane content may have a carbon intensity as low as 0.4 kilograms of CO₂ equivalent, or CO₂e,1per kilogram of hydrogen.
Table 1. Carbon intensities of different hydrogen production pathways2,3
| Type of Hydrogen | Carbon Intensity (kg CO2e/ |
| Fossil Fuel-Based Hydrogen | 10.0 – 13.0 |
| Fossil Fuel-Based Hydrogen + Carbon Capture | 0.8 – 6.1 |
| Electrolytic Hydrogen | 0.5 – 24.04 |
| Geologic Hydrogen | 0.4 – 1.55 |
- Potential scalability. Some estimates suggest that trillions of tons of geologic hydrogen may exist underground. Even accessing a small fraction could satisfy global hydrogen demand for centuries. Certain reservoirs may even replenish through ongoing geological processes, though this remains under study.
- Potentially low cost. Early evidence from exploration wells in Mali, Spain, and Australia suggests production costs could be as low as $0.50–$1.00 per kilogram, significantly cheaper than other clean hydrogen pathways.
What don’t we know about geologic hydrogen?
Despite geologic hydrogen’s vast potential, there is still a long road ahead in understanding the role this unique energy source can play in the energy transition. Perhaps one of the most pressing challenges is that the industry has very limited real-world experience. Most extraction methods are still experimental, and the only operating project — in Mali — produces just a few tons of hydrogen per year for local electricity. That proof of concept is important but insufficient to demonstrate whether geologic hydrogen can scale to meet global demand.
Exploration itself is expensive and risky. A drilled well may find little or no hydrogen, or the resource may be too deep, diffuse, or remote to extract economically. The environmental impacts of exploration and purification are also not yet fully understood. Geologic hydrogen is rarely pure, often mixed with methane or other gases. If methane leaks or is flared during extraction or purification, the climate benefits could be significantly diminished.
Infrastructure gaps add another layer of uncertainty. Hydrogen deposits may not align with areas of demand, requiring new pipelines, storage, and transport.
A cautious path forward
Though geologic hydrogen could one day be a valuable clean hydrogen source, the path forward is still uncertain. More data is needed to better understand the potential of this emerging energy source. That starts with carefully designed real-world demonstration projects – even if they start small in scale – and sustained research and development to better understand the fundamentals: how hydrogen forms, accumulates, and behaves underground. At Clean Air Task Force (CATF), we will continue monitoring this space and advocating for science-led, responsible, and informed exploration of geologic hydrogen, not just hype.
For readers looking for more technical detail on geologic hydrogen’s formation processes, carbon intensity, and extraction methods, see CATF’s technical brief on geologic hydrogen.
