The invention relates to a method and a device for cleaning contaminated used oil, in which starting material is heated to the gas phase and the resultant vapor is rectified, with purified oil being removed as condensate from a drain in a rectification column. This enables efficient operation even in the smallest of systems, such that a compact system configuration and thus in particular mobile use by a container structure is made possible. The invention also reduces the cost required for servicing. The used oil is subjected to an evaporation process by at least indirectly placing the starting material in contact with a melting bath, the melting temperature of which is above the evaporation temperature but below the ignition temperature of the used oil, and by rectifying the vapor in the rectification column.