A process-based model for the consumption of atmospheric methane (CH4) by soils was developed to identify the most important factors affecting uptake rates and to determine whether the current uncertainties in the estimated size of the global soil sink might be reduced. Descriptions of diffusion and microbial oxidation processes, which together determine the CH4 flux, were included. The results suggest that the global sink strength lies within the range 20--51 Tgyr-1 CH4, with a preferred value of 38 Tgyr-1 CH4. Dry tropical ecosystems account for almost a third of this total. Here microbial activity rather than diffusion is limiting uptake. It is also in these areas that the impact of any intensification in agriculture will be the most pronounced, with a possible future reduction in uptake in excess of 3 Tgyr-1 CH4. This is in contrast to the overall impact of global warming, which is expected to leave the size of the global soil sink relatively unchanged. ¿ 1999 American Geophysical Union