The removal of rolling oil from the surface of coiled sheet metal is characterized by two stages : volatile components desorb easily and are removed through laminar flow in the channels within the coil, while nonvolatile constituents of the oil decompose in the presence of oxygen. In order to do so, the oxygen must diffuse into the channels of the coil, where it reacts with the oil, thereby forming products which again leave the coil by diffusion. A model has been developed to describe this behavior.