Abstract Dilution of anoxic slurries of paddy soil resulted in a proportional decrease of the rates of total methanogenesis and the rate constants of H 2 turnover per gram soil. Dilution did not affect the fraction of H 2/CO 2-dependent methanogenesis which made up 22% of total CH 4 production. However, dilution resulted in a ten fold decrease of the H 2 steady state partial pressure from approximately 4 to 0.4 Pa indicating that H 2/CO 2-dependent methanogenesis was more or less independent of the H 2 pool. The rates of H 2 production calculated from the H 2 turnover rate constants and the H 2 steady state partial pressures accounted for only < 5% of H 2/CO 2-dependent methanogenesis in undiluted soil slurries and for even less after dilution. Upon dilution, the Gibbs free energy available for H 2/CO 2-dependent methanogenesis decreased from −28.4 to only −5.6 kJ per mol. The results indicate that methane was mainly produced from interspecies H 2 transfer within syntrophic bacterial associations and was not significantly affected by the outside H 2 pool.