The oxidation of nickel gauze catalysts by O-2 was investigated by transient response methods. Qualitative description of the experimental transient responses have shown that the oxidation of metallic nickel proceeds in two stages. The first step is a fast dissociation of gaseous oxygen on the catalytic surface, followed by oxygen diffusion from the surface into the bulk. This slow second step explains the long tailing observed from the experimental transient responses. Furthermore, a rise of temperature was observed during the nickel oxidation. A kinetic model has been developed on the basis of the experimental results in order to provide quantitative information about this reaction. For nickel gauze oxidation, a non-isothermal model combining the subsurface oxygen diffusion with an exponential distribution for the activity of surface sites gave a good agreement with experimental transient data. As a result, the activation energies and the pre-exponential factors of the rate constants as well as the characteristic oxygen diffusion times were determined. (C) 2003 Elsevier Ltd. All rights reserved.