The physical appearance of oil was investigated in three types of oil-contaminated sediment: (1) natural harbour sediment, (2) laboratory samples of sediment prepared by simulating the natural oil-sediment interaction processes and (3) laboratory samples of spiked sediment prepared by direct mixing of large volumes of oil and sediment. Microscopic observations show the possible presence of three oil phases in the sediment: (1) distinct oil droplets, (2) oil coating on sediment particles and (3) 'oil patches'. Through quantitative investigations, it was concluded that the division of oil in the different phases is affected by the oil-sediment interaction processes, oil type, and oil concentration. As far as the droplet phase is concerned, these processes and parameters also influence the droplet size distribution. (C) 2003 Elsevier Science Ltd. All rights reserved.