Natural hydrogen is considered a potential low-carbon energy source. But how much is generated underground—and how quickly? An international research team led by the LIAG Institute for Applied Geophysics in Hannover has published the first process-based estimates for the Western Pyrenees and Northern California in Nature Communications. The calculated production rates are lower than earlier theoretical estimates. The study’s new evaluation method, through the open-source tool PoNHy, allows more realistic assessments and can be applied to other regions to identify promising geological systems more precisely and evaluate their potential.