The effect of a nonporous ultrafine iron oxide precursor, prepared by a flame method, was evaluated in the hydroliquefaction of a bituminous coal in tetralin (350, 400, 430 degrees C) on a laboratory scale, and compared to that of other aerosols (silica, alumina, SnO2, MoO3, NiMo/Al2O3). The precursors were sulfided with S during heating, according to a previously established conditions set. Methods of evaluating catalytic activity in hydroliquefaction runs based on extraction yields are strongly dependent on the experimental conditions. Special emphasis has been given here in the application of two alternative parameters based on electron spin resonance (ESR) data, and on the ratio of hydrogen consumption from the gas to that from the solvent (H-gas/H-solv). Our results show that with increasing the temperature, the lower the differentiation between catalysts measured by extraction conversions. However, H-gas/H-solv and the measurements by ESR of the stable radicals of the tetrahydrofuran-insoluble fractions are more clearly affected by the nature of the catalysts and related at a given temperature. Fe2O3 and MoO3 are the most active catalysts at 30 degrees C. The order of activity is the same regardless of the method used. The spillover effect can explain the hydroliquefaction mechanism. At 400 degrees C, H-gas/H-solv permits the dearest differentiation between catalysts. At this temperature, effects other than spillover can contribute to hydrogen-transfer mechanisms. Analytical data of the coal-derived liquids (capillary gas chromatography, size exclusion chromatography, and extrography) show a large temperature effect, independent of the nature of the catalyst : as the temperature increases from 400 to 430 degrees C, the percentage, in the oils, of the four or more ringed compounds decreases, and the heaviest components of the asphaltenes are degraded. Furthermore, the oils obtained with sulfided Fe2O3 or MoO3 contained significantly more two-ringed aromatic compounds than the oils obtained with the other catalysts, or with no added catalyst. Possible explanations are discussed in the light of the literature research with model compounds.