INTRODUCTION The rapid increase in the demand for and utilization of petroleum and petrochemicals has resulted in an increasing level of petroleum contamination of marine and estuarine waters. With the introduction of supertankers and the increased development of offshore oil deposits around the world the problem of petroleum contamination of marine and estuarine habitats can be expected to continue@ It has been estimated by Charter et al. (1973) that the total annual influx of oil into the ocean is approximately 3 million tons per year@ most of this being concentrated in the biologically important estuaries and near shore marine waters. Because of this@ concern has grown in recent years about the effects of oil on marine organisms and ultimately on the marine environment as a whole. Our present knowledge of the impacts of petroleum pollution on marine and estuarine organisms and environments originates primarily from two sources: field studies following major oil spills@ and laboratory investigations of the toxic or sublethal effects of petroleum and specific petrochemicals on selected marine plants and animals. Both approaches can provide valuable information upon which to base predictions of the potential environmental consequences of chronic or acute oil pollution.