Mantle8

Hydrogen is considered one of the pillars of the energy transition, but its current production remains costly and energy-intensive. Mantle8 works on a different frontier: natural hydrogen — hydrogen that forms spontaneously in the depths of the Earth's crust through geochemical reactions, and which could be extracted directly from the subsurface without needing to produce it artificially. Founded in Grenoble in 2019, the startup has developed HOREX®, a proprietary multiphysics platform that generates 4D images of active underground hydrogen systems. Combined with the Geological Trifecta — an exploration framework that identifies the convergence of a hydrogen-generating source, continuous replenishment mechanism, and sufficiently sealed reservoir — HOREX® allows Mantle8 to select with high probability of success the sites where to drill. In May 2026, the startup closed a €31 million Series A led by Sandwater, with participation from Breakthrough Energy Ventures (Bill Gates' clean energy fund), Bpifrance through the Ecotechnologies 2 fund, IP Group, Wind Capital, and Calderion. The round will fund what the company calls 'the world's most advanced natural hydrogen exploration and drilling campaign'. Mantle8 positions itself at the intersection of computational geoscience and climate deeptech: if the thesis proves correct, natural hydrogen could become one of the strategic energy resources of the next decade, extracted with minimal environmental impact compared to grey hydrogen and at a competitive cost compared to green hydrogen.