A one-dimensional mathematical model is presented to describe biochemical reactions and diffusion occurring within massive seafloor gas hydrates. Methanogenesis and anaerobic methane oxidation coupled with sulfate reduction are the two reactions analyzed with emphasis on gas hydrate stability. Many numerical simulations are being developed to predict gas hydrate formation, dissociation, and stability. The model complements these simulations as a subunit by incorporating the consequences of kinetic and transport processes occurring within seafloor gas hydrate capillaries. Better predictions of gas hydrate stability will assist in understanding the role of gas hydrates in the global carbon cycle. particularly as pertaining to global warming. (C) 2009 Elsevier Ltd. All rights reserved.