Field experiments were carried out to compare the littoral fate and ecological effects of chemically dispersed oil and nondispersed oil. The basic experimental design was a series of treatments applied to marked plots on rocky shores, a salt marsh, an intertidal sea-grass bed, and sand and mud flats. The treatments included a variety of oils and the dispersants BP 1100 WD, BP 1100X, Corexit® 8667, and Corexit 7664, applied directly to the intertidal plots. Results from treatments on intertidal rock suggested that oil deposition or oil deposition followed by dispersant cleaning had a greater effect than dispersant cleaning alone on limpets (Patella spp.) and small winkles (Littorina spp.). On the salt marsh, oil or oil followed by dispersant cleaning significantly reduced the density of the perennial grass Spartina anglica C.E. Hubbard and the annual plant Salicornia spp. Dispersant alone had relatively little effect on the vegetation. On the sea-grass bed, although variability was high, all treatments reduced the percentage cover of the sea-grass Zostera noltii Hornem. Sediment hydrocarbon analysis indicated little long-term retention of applied oil (whether dispersant treated or not) in the salt marsh mud and in muddy sand on a waterlogged intertidal flat. However, in the sea-grass bed sediments and in the fine sands on freely draining intertidal flats, dispersant-treated oil was, in some cases, retained at greater concentrations than untreated oil. The results are discussed with reference to the rocky shore Exposure Scale of Ballantine, to the shoreline Vulnerability Index of Gundlach and Hayes, and to factors such as the behavior of the water table, particle size, and depth of disturbance of sediments.