Differential thermal analysis (DTA) has been used as a method to study the self-heating behaviour of fresh and oxidized coals. Oxidation was performed in air at 200 degrees C for periods of up to 72 h. Six coals ranging from a High A Bituminous coal to a semi-anthracite were used. As the rank of the coal increases, both the self-heating and the end of combustion temperatures also increase. The total heat loss (area under the DTA curve) increases with the rank of the coal. An increase in the self-heating temperature, a decrease in the temperature of the end of combustion and a decrease in total heat flow were observed as a consequence of coal oxidation. A relationship between the total heat loss and the calorific value as determined using the ASTM standard method is pointed out.