The work to be described in this paper, is a study of chemical reaction between iron surfaces and various representative extreme pressure (EP) agents, such as chlorine type, sulfur type, Zn-dithiophosphate type, and the mixture of sulfur and chlorine type EP agents, by using the hot wire method. It has been observed that the corrosion rate of iron follows the parabolic law or the cubic law. The parabolic law can be explained by the diffusion mechanism of corrosion. In order to explain the cubic law, the corrosion retarding action of a barrier film has been assumed. From the X-ray analysis of reaction products, the complexity of corrosion process has been revealed. Zinc-diisobutyldithiophosphate has shown the characteristic behavior in the corrosion process, showing retardation against the corrosion. With a binary additives system, the joint reaction of sulfur and chlorine compounds on iron could not be satisfactorily supported in the scope of this study. Some interesting considerations are given for the correlation between chemical reactivity and load carrying capacity of oils containing EP agents.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in San Francisco, Calif., October 18–20, 1965.