Tests have been performed using a vacuum residue from the Middle East and its subfractions, pentane solubles (C5S), pentane insoluble-hepane solubles (C5IC7S), and heptane insolubles (C7I), as feedstock in different solvents, to evaluate their ability upon coke formation. The feedstock including those three subfractions produced a negligible amount of coke (1-1.2 wt %) and 14.7-16.7 wt % asphaltene; the latter was formed more in the feedstock (9.4 wt %), at 420 degrees C. There was no significant effect on coke and asphaltene formations in the products depending upon the solvent used in the tests. Heptane-soluble subfraction (C7S) formed 9.2-13.6 wt % asphaltenes but no coke at 420 degrees C using 1-methylnaphthalene and decahydronaphthalene, while the asphaltene contents were only 2.4-6.0 wt % in the case of C5S. The properties and average molecular structural parameters indicated that C5S included only 5.1 aromatic rings per average fused ring system, while C5IC7S and C7I contained 8.3 and 10.1 aromatic rings, respectively, which showed that C5IC7S was much closer to C7I than C5I. The results suggest that removing C5IC7S from the subfractions is very effective in suppressing coking trouble during upgrading.