As a result of experimental oxidation tests on seven coals from different sources, it has been found that not one but two models are needed to distinguish between large pore and small pore coals. The earlier Kam-Hixson-Perlmutter (KHP) model which was based on the expectation of very small diffusion rates for gases into coal, remains valid for the largest group of coals tested, but has to be modified for at least two of the coals. When the coals had relatively large pore volumes in the size range greater than 300A, the oxidation rate was found to be sensitive to particle size, gas float rate, and reaction temperature, in a manner indicating significant transport effects. Correlations of the CO2 to CO ratio obtained from runs under varying conditions also support the applicability of the KHP model. The heating values among the various coal samples changed upon oxidation in a manner dependent primarily on the changes in carbon content of the coal.