The effect of the mineral matrix of Turkish Goynuk and US Green River oil shales and air diffusion on the conversion of organic material in oxidation reactions was investigated in the present study. The material washed with HCl from the original oil shales, mainly carbonates of calcium and magnesium, had a mild catalytical effect and the material washed with HF, silicate minerals, had an inhibition effect during oxidation reactions of organic material. The overall reaction orders from the kinetic analysis were found to be pseudo-first-order. The magnitude of the activation energies of oxidation reactions at equal heating rates changed as E-a (HCl washed shale) > E-a (original shale) > E-a (HCl + HF washed shale). The rate of reaction depends on the rate of transport of the gas into the zone of reaction by diffusion. It was observed that the diffusion of oxygen into the organic matrix was the major resistance controlling the rate of oxidation reactions. (C) 2000 Elsevier Science Ltd. All rights reserved.