In the work, a chemical demetallation agent was used to convert entrained nonfilterable metals into a form which could be effectively removed by filtration. Two different types of chemical demetallation agents were used: metallic borohydrides (NaBHaub4 and KBHsub4) and diammonium phosphate (DAP). Several types of used oils having different metal contents were examined. It was observed that metallic borohydrides were highly selective with regard to the types of metals they removed and the accompanying sludge formed made the separation operation inefficient. On the other hand, results obtained with DAP were extremely favorable. The presence of water during the reaction was found to play an important role as a carrier for the DAP. The study also found the use of both sedimentation and filtration separation techniques to be practical, with filtration rates being significantly accelerated by the addition of low percentages of No. 2 fuel oil.