ABSTRACT The effects of API Reference South Louisiana crude oil upon four larval stages of American lobster Homarus americanus were determined in a flow-through system. Tests were conducted with naturally hatched animals in individual test chambers as well as in mass culture systems in an operating state lobster hatchery. Experimental flow-through crude oil exposure concentrations were 0.1@ and 1.0 ppm@ administered as a strongly agitated oil emulsion to ambient temperature seawater ranging from 15??? 20?? Oil exposure residence times ranged from 0.8 ?? 5.6 minutes depending on the test. Exposed animals were monitored six times daily for feeding behavioral characteristics@ mobility@ molting success@ growth and development times to reach the fourth larval stage. Pigmentation analyses were performed on individual larva by photomicroscopy@ followed by chemical analyses for hydrocarbons in seawater. Post-larval development through the eighth stage was investigated. Statistical comparisons were made among different control animals and between control and oil-exposed larvae.