Gas hydrates, the most common terrestrial example being methane hydrate (CH4?nH2O where n g 5.75), are crystalline solids formed from the association of water and gas under certain conditions of relatively high pressure (P) and low temperature (T). They continue to generate considerable interest as globally distributed deposits harboring potential hydrocarbon reserves, as icy minerals of predicted outer-solar-system occurrence, as manufactured materials with novel industrial applications, as potential players in global issues of climate and seafloor stability, and as troublesome blockage-formers in gas pipelines.