For the past half-decade, dozens of companies around the world have been hunting for buried stores of hydrogen, called natural or geologic hydrogen. This approach, known as stimulated geologic hydrogen or engineered hydrogen, turns subterranean rock formations into giant hydrogen factories. “I got the epiphany that geologic hydrogen is not just an accumulation; it’s a chemical reaction,” he says. Finding large accumulations of geologic hydrogen entails stumbling on a Goldilocks set of conditions. A back-of-the-envelope calculation convinced him that the cost of stimulated geologic hydrogen could easily compete with hydrogen made from methane.