The oil spill risk analysis (OSRA) model is an environmental impact assessment tool, producing estimates of the probabilities of oil spill occurrence and contact from prospective commercial oil and gas operations, which may occur broadly on the outer continental shelf of the United States. Extensive environmental data sets drive the model. Much of the data were obtained by numerous MMS-funded environmental studies. The model differs from most trajectory models in that it does not attempt to replicate or predict individual oil spill events. Instead, the model generates an ensemble of thousands to hundreds of thousands (typically) of simulated oil spill trajectories over many years of wind and ocean current input fields. The frequencies of contact of the simulated spills are the estimated probabilities under the implicit assumption that the input spill occurrence rates, winds, and ocean currents will be, in a broad statistical sense, like those that will occur during future oil and gas operations proximate to areas of environmental concern. Published by Elsevier Ltd.