Static bioassays of 24 hours' duration were performed on samples of wastewaters provided by 22 domestic petroleum refiners. These wastewaters represent three types of water discharges prevalent to this industry: process wastewaters prior to dilution with other streams; API separator effluents which are a conjugate of various streams within a refinery; and wastewaters following treatment by activated sludge systems. Bioassays were performed using redear sunfish (Lepomis microlophus) as test organisms. Twenty-four hour 50 percent tolerance limits (TL sub 50) of the various wastewaters are compared with results of chemical analyses performed during the same study. Toxicity varied considerably both between refineries and for waste streams from within a single refinery. Results of these analyses and observed behavioral symptoms of distressed fish revealed that ammonia, sulfides, and phenolics, alone or in combination, were major contributors to toxicity exerted in most samples. Three refineries had samples which were more toxic than anticipated based on results of chemical analyses, indicating the presence of other toxic compounds in unknown quantities; e.g., various hydrocarbons.