The swelling ratio of Wandoan coal is related to the amount of total huminite as well as fluorescing huminite. The highest swelling ratio is observed in the 1.25-1.30 density fraction, which also has the highest content of fluorescing huminite. The Illinois No. 6 coal contains less fluorescing and more nonfluorescing vitrinite compared with Wandoan coal and shows only a general increase in its swelling ratio with increasing vitrinite content. The Illinois coal does not swell properly as a result of poor solvent penetration due to the presence of less porous, nonfluorescing telocollinite. The coal dissolves at 300 degrees C because increased vesiculation results in an increase of external and internal dissolution relative to swelling The study shows that the swelling ratio of coals is related to maceral composition, which in turn, is a reflection of the environment of coal formation.