A Spanish low rank coal was hydrogenated without solvent in the presence of a molybdenum catalyst. The asphaltenes and derived residues were analysed to obtain an understanding of the behaviour of the coal under hydrogenation conditions and the influence of a previous extraction with chloroform, as well as reaction time and temperature, on the structure of the products obtained. Under the reaction conditions used, with tubing bomb reactors and an initial hydrogen pressure of 7 MPa, the data obtained for this coal show that an increase in temperature from 350 to 400 °C, and of reaction time from 5 to 60 min gives, in general, lower content of organic matter in the residues. The two variables have opposing effects on the aromatic content of the asphaltenes. Increasing reaction time reduces the aromaticity, whereas increasing the temperature will increase aromaticity. Prior extraction of the low molecular weight chloroform-soluble compounds increased conversion, and resulted in asphaltenes with higher content of aromatic- and oxygen-containing groups.