Samples of lignite and bituminous coal were subjected to interaction with dry and moist oxygen. It has been found that within the low-temperature range used, the decisive source of the exothermic effect was the adsorption heat of water vapor, and the temperature of coal did not exceed 100 degrees C regardless of the mode of its previous contact with air oxygen. At temperatures above 100 degrees C, the only observed result of the coal interaction with oxygen was the formation of a layer of oxidation products on the coal surface. It was established that the oxidation reaction induced close to but below the ignition temperature was unable to overcome, by its heat effect, the small temperature difference required for the ignition of coal; on the contrary, the surface oxides formed increased the ignition point. The amount of oxygen bonded by both the physical adsorption and chemisorption was determined by direct measurements. It has been assumed that the interaction of coal matter with oxygen below the ignition temperature leads to the inactivation of the coal surface without the thermal effects necessary for coal ignition.