Four typical DOs supplied from Japanese refineries were analyzed in detail by GC, FD-MS1H and13C-NMR after the fractionations by column chromatography. A DO carries 30% saturate and 70% aromatic fractions. The saturate consisted principally of the straight paraffins. The aromatic fraction was separated into five substractions(AR1 -AR5 ) of which contents distributed rather evenly, the middle fraction(AR 3) occupying the largest of 30%. The aromatic components had consisted of aromatic rings from 2(AR1) to 4(AR4+5), of some aryl-aryl linkages and naphthenic rings being included. The lighter aromatic fraction carried more alkyl groups, enhance its solubility and elution in the column. B DO appeared heaviest among the DOs in the present study. The oils carried only 10% of the saturate and 75% of AR3-AR5 aromatic subfractions. Its saturate was of carried rather short chains and more isoparaffins. Its aromatic components had very similar aromatic units to those of A DO in the same subfraction, although the heaviest fraction of the former one contained also a small portion of 6 aromatic rings F and G DOs were very similar to A DO in the fractional distribution and component structure, although the latter carried more amounts of heavier aromatic fractions. Such results of structural analyses were compared to the coke yields under atmospheric pressure, where only heavier aromat.ic.fractions were converted into the coke. The molecular size and aromaticity of the fractions are concerned for such a correlation.