Loy Yang brown coal treated with cobalt acetate/ammonium molybdate (Co/Mo) gave lower conversions than the very high values obtained for the same coal treated with nickel acetate/ammonium molybdate (Ni/Mo) when reacted with hydrogen at 400 degrees C. The difference in conversions obtained between the two catalyst systems decreased with increasing time. Addition of sulphur as carbon disulphide (CS2) eliminated the difference between the Co/Mo and Ni/Mo catalyst systems, but neither system was more active than a sulphided Mo catalyst. Addition of a hydrogen donor solvent, tetralin, to a reaction in the absence of sulphur decreased conversion for the Ni/Mo catalysed system, but increased that for the Co/Mo system. The order of activity in reactions without solvent or added sulphur for the coal treated with the individual metals was Co similar to Mo < Ni. In the presence of sulphur the order was Co much less than Ni < Mo; the addition of sulphur led to no significant improvement with Co catalysts.