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In recent years, serpentinized ultramafic rocks have received considerable attention as a source of H₂ for hydrogen-based microbial communities and as a potential environment for the abiotic synthesis of methane and other hydrocarbons within the Earth’s crust. Both of these processes rely on the development of strongly reducing conditions and the generation of H₂ during serpentinization, which principally results from reaction of water with ferrous iron-rich minerals contained in ultramafic rocks. In this report, numerical models are used to investigate the potential influence of chemical thermodynamics on H₂ production during serpentinization. The results suggest that thermodynamic constraints on mineral stability and on the distribution of Fe among mineral alteration products as a function of temperature are likely to be major factors controlling the extent of H₂ production. At high temperatures (>∼315°C), rates of …