Ni/Mo and Co/Mo are two of the most commonly used and effective catalysts used in coal liquefaction. Recent work has reported a similar to 40 wt% difference in conversion between Ni/Mo and Co/Mo-treated Loy Yang brown coal hydrogenated at 400 degrees C without added solvent or sulfur. However, this study shows that under the same reaction conditions the difference in conversion between Ni/Mo and Co/Mo-treated coal decreases with increasing carbon content (rank) of the coal (Wyoming, Wadge, Surat Basin). Furthermore, for a bituminous Surat Basin coal the pattern of catalytic activity of Ni, Co, Mo and their combinations differs from that for a brown (Loy Yang) coal as follows. In no-solvent, no-added-sulfur hydrogenations, the catalytic activity of the individual metals was much greater for the Surat Basin coal, but the increased activity of Ni and Co did not carry over to increased promotion of Mo catalysis by these metals. The effect of added sulfur on the activity of the individual metals was also different for the two coals. The distribution of the catalyst metals in the coal particles was different in the Loy Yang and Surat Basin coals, but this cannot explain all the observed differences in catalytic behaviour.