As a consequence of recovering, transporting, and using oil, petroleum hydrocarbons are being introduced into the biosphere—and primarily into the oceans—to an unprecedented extent. Estimates of the amount of oil reaching the sea range from one to ten million metric tons per year (), with the most probable rate being near the middle of this range. Most of this comes in small but continuous doses from tanker operation, industrial discharge, and on-shore waste disposal practices. Producing less effluent but disproportionately more public attention and research effort are the large accidental oil spills. Prospects for the immediate future are that both types of discharge will increase as transport tonnage and off-shore exploitation efforts increase.

Faced with this problem and the need to make immediate and intelligent decisions affecting our future, government, industry, the scientific community, and the public are dealing with questions for which there are often no conclusive answers. The extreme diversity of opinion, compounded by overblown statements from one extreme or the other, is the result of too little information and frequent misunderstanding of available information. The literature on the ecological effects of oil pollution is surprisingly voluminous, and several extensive reviews of the subject have recently appeared ().

Our overview of the ecological effects of oil pollution attempts to answer the need for an evaluation of available information and of the conclusions drawn from this information. Directed to decision-makers, it is intended as a supplement to more detailed reviews and to the scientific literature itself rather than as a substitute for them. Included are a review of available research on biological effects, ordered by biological community type, a summary of information concerning long-term effects, a discussion of methods and how they influence results and conclusions, and an appraisal of the present direction of research dealing with oil.