Hydrogen exchange reaction of three Argonne coals (Illinois No. 6, Upper Freeport and Pocahontas #3) and Wandoan coal with tritiated gaseous hydrogen were performed at several temperatures. Hydrogen exchange reaction was performed in a flow reactor packed with 0.4 g of coal and 0.05 g of catalysts under the following conditions: pressure 15 kg/cm(2), temperature 200, 250, 300degreesC, carrier gas H-2 or N-2 5 ml/min. When a pulse of [H-3]H-2 was introduced into a coal in H, carrier gas at several temperatures, the delay of [H-3]H-2 pulse observed increased with increasing the reaction temperature and decreased with increasing coal rank. Further in the reaction of tritiated coals with gaseous hydrogen at constant temperature, the hydrogen exchange rate was estimated from the release rate of [H-3]H-2. The apparent hydrogen exchange rate at 200degreesC was higher than that at 250degreesC. This shows that the hydrogen with low reactivity came to participate in the reaction at high temperature. When the reaction of tritiated coal with gaseous hydrogen was performed during heat treatment, one, two or three peaks of tritium concentration were observed in the outlet of the reactor depending on temperature (200, 250 or 300degreesC, respectively) at which tritium was incorporated into coal initially. It was suggested that there were at least three kinds of hydrogen with different reactivity in coal. (C) 2002 Elsevier Science Ltd. All rights reserved.