In bitumen extraction of oil sands by hot water, the problem of sludge accumulation is, at least partially, attributable to the presence of unrecovered bitumen as well as acetone solubles and so called ‘insoluble organic matter’ (IOM) on the surfaces of inorganic particles. A comparative study of the bitumens separated from both sludge and the original oil sands feed suggested that the former was depleted in high molecular weight fractions. Examination of the organic matter extracted from sludge with acetone indicated that asphaltene constituents, as well as long chain fatty acids, could report with the acetone solubles. The structural parameters of the IOM derived from sludge were, in general, similar to those for oil sand IOM.