The primary objective of this study was to evaluate the application of dispersant to spilled oil as a means of reducing adverse environmental effects of oil spills in nearshore, tropical waters. The results of numerous laboratory and field studies have suggested that dispersants may play a useful role in reducing adverse impacts on sensitive and valued environments such as mangroves, seagrasses, and corals. However, the use of dispersants has not been allowed thus far in most situations because of a lace of direct experimental data on the various effects of dispersants and the environmental trade-offs presumed to occur as a result of their application to crude oils. To accomplish this objective, a 2 1/2 year field experiment was designed in which detailed, synoptic measurements and assessments were made of representative intertidal and nearshore subtidal habitats and organisms (mangroves, seagrass beds, and coral reefs) before, during, and after exposure to untreated crude oil and chemically dispersed oil. The results were intended to give guidance in minimizing the ecological impacts of oil spills through evaluation of trade-offs in the relative impacts of chemical dispersion to tropical marine intertidal and subtidal habitats.