Most research on the effects of petroleum in aquatic systems has concentrated on the immediate and short‐term toxic effects. This review collates and evaluates the results of research concerned with the effects of sublethal concentrations of petroleum hydrocarbons on aquatic organisms and to a lesser extent, ecosystems, and considers some of the implications for human health. The available information on quantities of petroleum hydrocarbons which are released into the sea as well as the concentration and types which occur in oceanic areas is presented. The various mechanisms by which hydrocarbons can enter different classes of aquatic organisms are outlined, as well as storage, metabolic, and excretion processes. This information is utilized in applying to petroleum hydrocarbons the mathematical modeling principles which have been developed during investigations of other environmentally persistent substances. In this context the behavior of petroleum hydrocarbons in food webs is considered, particularly the possibility of biological magnification. The available information on physiological and behavioral responses to sublethal concentrations of petroleum hydrocarbons is reviewed. In various areas the petroleum contamination of aquatic organisms used as food has occurred. The incidence of tainting in seafoods and the significance of human exposure to petroleum‐derived carcinogens is considered.