Abstract: The invention relates to a method for reprocessing waste oils and producing high-grade base oils, whereby waste oil is treated by means of distillation, thin-film evaporation in a high vacuum, optional fractionation for separation into layers of different viscosities and subsequent extraction with N-methyl-2-pyrrolidone and/or N-formylmorpholine. The invention also relates to base oils that can be obtained by said method and to the use thereof. The inventive method is characterized in that approximately any waste oil can be used, including waste oils with polychlorinated biphenylene (PCB) or PCB substitutes with contents of up to 250 mg/kg. Furthermore, waste oils containing up to 5% vegetable oil can be present in the waste oil that is to be reprocessed without impairing the quality of the base oil. The undesirable constituents, especially polycyclic aromatic hydrocarbons and polychlorinated biphenylenes (PCB) or the substitutes thereof are removed in an almost quantitative manner.