Abstract: A process for reclaiming used hydrocarbon oils through prepurification by means of coagulation, adsorption, filtration, distillation, and after-treatment, wherein said oils are prepurified and then dehalogenated, fractionally distilled and hydrogenated. It is preferred that for the prepurification, said coagulation and said adsorption are carried out by means of a hydroxide or hydroxide mixture, preferably aluminum and/or ferric hydroxide, in a proportion of 0.5 - 5.0% by weight, preferably 1-2% by weight, of hydroxide relative to said used oil at a reaction temperature of from 20.degree. - 200.degree. C, preferably from 50 to 150.degree. C, said hydroxide or hydroxides being produced directly in said used oil in the presence of water or being introduced into said used oil in the form of an aqueous slurry.