Abstract: A process is disclosed for reprocessing contaminated oils, such as used crankcase oil from automobile engines, by thermal treatment, such as visbreaking, in the presence of other hydrocarbon feedstocks, followed by fractional distillation for the recovery of a gasoline fraction, a carboxylic acid fraction, a gas oil fraction containing chlorinated hydrocarbons and a high boiling bottoms fraction. The gas oil fraction is subjected to catalytic hydrocracking with the simultaneous destruction of chlorinated hydrocarbons. The resulting hydrocracked oils, after separation of hydrogen chloride, are free from chlorine compounds and other contaminants.