The state-of-the-art in oil spill modeling is summarized, focusing primarily on the years from 1990 to the present, All models seek to describe the key physical and chemical processes that transport and weather the oil on and in the sea, Current insights into the mechanisms of these processes and the availability of algorithms for describing and predicting process rates are discussed. Advances are noted in the areas of advection, spreading, evaporation, dispersion, emulsification, and interactions with ice and shorelines. Knowledge of the relationship between oil properties, and oil weathering and fate, and the development of models for the evaluation of oil spill response strategies are summarized. Specific models are used as examples where appropriate. Future directions in these and other areas are indicated. (C) 1999 Elsevier Science Ltd. All rights reserved.