The toluene-insoluble (TI), asphaltene (A), and heavy oil (HO) fractions were isolated from three centrifuged SYNTHOIL liquid product (CLP) samples, prepared under different process conditions at 45O"C, 27.6 MPa hydrogen pressure from the same feed coal, Kentucky hvAb, from Homestead Mine. Run FB 53 was made with CoMo catalyst, 1 l-min preheater residence time, and 3-min reactor residence time. The much higher viscosity of FB 53-59 compared to FB 53-1 correlates with the larger contents of its toluene-insolubles and asphaltene, larger oxygen and sulphur contents of its asphaltene and toluene-insolubles, larger molecular weight and smaller aromaticity of its asphaltene, and the larger enthalpy of interaction (AHO) of its asphaltene with quinoline in benzene. The average molecular weight and percentage of heteroatoms of the heavy oil from FB 53-59 are also greater than that from FB 53-1, and the value of AH O of the heavy oil with quinoline, follows the same order. Run FB 57 was made with glass pellets, 17-min preheater residence time and 6-min reactor residence-time. Since in FB 53-59 the CoMo catalyst has lost part of its activity, a comparison of FB 53-59 with FB 57 yields information on the effect of residence times on the properties. The toluene-insoluble and asphaltene contents, as well as the viscosity, of FB 53-59 is larger, while the heavy oil content of FB 53-59 is smaller than that of FB 57. This comparison indicates that a larger-residence-time preheater and reactor may, to some extent, favour conversion as well as decrease the viscosity of the product oil. The values of AH0 for the interaction of quinoline with the heavy oil and asphaltene fractions obtained from the three CLP samples are in the order: FB 53-59 > FB 57-42 > FB 53-1, and they are attributed to the varying degree of hydrogen-bonding effects involving largely aromatic phenols which serve as hydrogen donors to quinoline