Hydrogen transfer reactions of coal with tritiated gaseous hydrogen in the presence of tetralin were performed using a flow reactor under the following conditions: pressure 50 kg/cm(2), temperature 200-400 degreesC, and reaction time 120-420 min. When Wandoan coal (WA) was used as a coal sample, functional groups participated in the hydrogen transfer reaction even at 200 degreesC and then decomposed at 250 degreesC. At 300 degreesC, ether bonds were cleaved to generate hydroxy groups which were decomposed at 350 degreesC. When the higher rank Pocahontas coal (POC) was used, functional groups participated in the hydrogen transfer reaction even at 250 degreesC and then decomposed at 300 degreesC. Further, ether bonds were cleaved at 350 degreesC to generate hydroxy groups which were decomposed at 400 degreesC. These results showed that in the case of POC coal, a 50 degreesC higher temperature was needed to obtain functional group behavior similar to the case of WA coal.