The authors investigated the effect of polyethylene glycol (PEG) application on the oxide removal action of cathode spots. Experimental observations revealed that the cathode spots formed on the oxide layer on the metal surface can be classified into two different sub-types, slow cathode spot (SCS) and fast cathode spot (FCS). Two different sub-types of cathode spots could exist in a same test piece at a same time. The removal rate of oxide depends on the mixture ratio between FCS and SCS. The more the cathode spots belonged to FCS, the faster the oxide layer is removed. The application of PEG enhances the probability of the presence of FCS. (C) 2003 Elsevier B.V. All rights reserved.