This report presents the results of studies undertaken to determine the extent of the problem resulting from the disposal of waste oils and the effect of various disposal techniques on the environment. The report is submitted in fulfillment of Section 104 (m) (2) of the Water Pollution Control Act Amendments of 1972. Waste lubricating oils contain a myriad of contaminants depending upon their usage. In general, they contain oxidation products, sediment, water and metallic particles resulting from machinery wear. The collection of waste oils from industrial operations and automotive service facilities is the weakest link in the overall waste oil recycling/disposal scheme. Disposal methods currently used include re-refining, use as a fuel for industrial and utility applications, use in road oils, asphalts and as a dust palliative, disposal in sanitary landfills, and surreptitious dumping on land or in water. The re-refining industry in the United States is discussed. Results of the biological studies to date are presented.