several samples of automotive lubricating oil produced from both new and used stocks were compared in chemical properties, including metals analysis, concentration of phosphorus, nitrogen, and sulfur; ash, acid number, and base number. selected bench-scale tests were used to compare and evaluate the quality of these used, re-refined, and new motor oils. most of the re-refined oils studied could not be distinguished from new oils by the laboratory tests. samples produced in-house and included in this comparative evaluation were obtained by treating used oil by one of three techniques: (1) solvent precipitation; (2) vacuum distillation; and (3) combined solvent precipitation and vacuum distillation. the combined treatment effectively removed sludge and contaminants from the used oil without causing serious change in the hydrocarbon composition of the oil base stock. reformulation of the re-refined oil with additives produced a lubricating oil comparable in quality to other oils of this study. 10 fig, 5 tables. (era citation 02:025904)