Mantle8, a natural hydrogen exploration company based in Grenoble, France, raised €31m (about $36m) in a Series A round, reported in mid-May 2026. Sandwater, a Norwegian investor, led the round.
Other participants were Breakthrough Energy Ventures, the Ecotechnologies 2 fund that Bpifrance manages on behalf of the French government, IP Group, Wind Capital and Calderion, an investment platform backed by Audacia, according to Hydrogen Central. The round brings Mantle8's total funding to €37m (about $44m), the company said. No valuation was disclosed.
“This raise reflects the growing conviction among leading clean tech investors that natural hydrogen is a resource worth pursuing at scale”Emmanuel Masini, founder and CEO, Mantle8
What Mantle8 does
Natural hydrogen is hydrogen that occurs underground rather than being made by electrolysis or from fossil fuels. Mantle8's chief executive and founder, Emmanuel Masini, said its existence is a well-established scientific fact and that the difficulty has been finding free accumulations of high-purity hydrogen that are commercially viable.
The company develops subsurface modelling and exploration technology. Its main platform, HOREX, is a multiphysics system that produces four-dimensional images of active underground hydrogen systems. Mantle8 says it completed the world's first 4D imaging of an active underground natural hydrogen system in the Hydrogeco project in the French Pyrenees.
It also uses an exploration framework it calls the Geological Trifecta, which looks for places where three conditions meet: an active source that generates hydrogen, continuous replenishment, and a reservoir that is sealed well enough to hold the gas.
The cost claim
Mantle8 says economic models project production costs as low as €0.80 per kilogram. H2 International reported that, if achieved, this would make natural hydrogen significantly cheaper than green hydrogen from electrolysis. The figure is a company projection, not a demonstrated result, and no reservoir has yet been drilled and proven.
The company says it aims to produce commercially viable natural hydrogen by 2030, and that it plans to partner with organisations that focus on drilling and exploiting target reservoirs so its technology can be rolled out quickly.
What the money is for
Mantle8 said it will use the capital over the next two years to fund what it calls the world's most advanced natural hydrogen exploration and drilling campaign. The platform will be used across its global pipeline to identify and rank the most promising sites. Those will then be drilled to confirm hydrogen accumulations and assess volume, purity and reservoir quality.
Bart Markus, the company's chairperson, said the next two years are about proving that the active hydrogen systems its technology has pinpointed can deliver sustained, commercially viable flow.
Tom Even Mortensen, founder and managing partner of Sandwater, said the team had built proprietary exploration technology, validated it in the field and has a clear plan to move into the commercial phase.
The funding so far
Mantle8 was founded in 2019. In 2025 it raised a €3.4m seed round led by Breakthrough Energy Ventures. Earlier in 2026 it received a €2.06m grant from the EU Just Transition Fund to industrialise its core exploration technologies, which is not counted as venture funding here.
Masini said the raise reflects growing conviction among leading clean tech investors that natural hydrogen is a resource worth pursuing at scale. The reports did not give headcount or revenue.
Company website: mantle8.com