Well-characterized coals of different H atomic ratio and rank were reacted at 365°C with CO, H 2 and CO-H 2 mixtures in water in the presence and absence of sodium aluminate. The optimum H 2 ratio for conversion was found to vary with the type of coal. It was <1:1 for low-rank and subbituminous coals, whereas the conversion of bituminous coals either did not vary with H 2 ratio or reached a maximum at a higher H 2 ratio (2:1). Even for a bituminous coal there was no advantage in reducing thewater ratio below 2:1 in NaAlO 2 -catalysed reactions. The conversions increased with increasing H atomic ratio of the coal and decreasing rank, with or without NaAlO 2 . Asphaltene yields increased with increasing coal rank and increasing proportion of CO in the H 2 -CO reacting gases. The mechanistic implications of these results are briefly discussed.