We investigated the relationship of geological environments on gas hydrate formation and stability by basin analysis of gas hydrate sites. Basin analyses were performed on 21 offshore locations with direct or indirect evidence of gas hydrates. Extensive geological investigations were conducted for each study region comprising one or more gas hydrate locations. Sediment composition, provenance, and depositional history were documented for each study region. Structural development of the sedimentary basin was determined using drilling results and seismic reflection profiles. Potential for generation of biogenic methane and conventional thermogenic hydrocarbons was assessed by analysis of existing geochemical data and by thermal modeling. All available seismic data, both published and unpublished, were examined for evidence of gas hydrates. Bottom simulating reflectors (BSRs) and other seismic anomalies were mapped. Drilling evidence of possible gas hydrates was reviewed. Based on the limited available information, conditional assessments of gas resources were derived. Quantities of gas contained both in the gas hydrate and possibly trapped beneath the gas hydrate stability zone were estimated. 93 refs., 37 figs., 2 tabs.