The effects of diluent composition on asphaltene precipitation from Cold Lake vacuum residue and Athabasca atmospheric tower bottoms were determined using the hot filtration method at 60-85 degreesC. For selected mixtures the temperature range was extended to 300 degreesC. The diluents include pure n-alkanes, a lube oil base-stock, a heavy vacuum gas oil and a resin-enriched fraction recovered from Cold Lake vacuum residue by supercritical fluid extraction and fractionation. The latter three complex diluents were tested alone and in blends, in order to cover a range of saturates from 56 to 99.4 wt%, aromatics from 0.6 to 25 wt%, and resins from 0 to 19 wt%. The scaling equation proposed by Rassamdana et al. [1] in which the weight percent of asphaltenes precipitated is expressed as a function of alkane to feed ratio, and the alkane molecular mass, gave good agreement with the data for the pure alkane diluents. For the more complex diluents, an extension to the scaling equation was developed with two additional variables (the density and saturate content of the diluents). This equation provided good agreement with the data over a wide range of diluent to feed ratios. By the addition of the colloidal instability index of the feed oil into the variables of the scaling equation, the precipitation data from the two different feed oils could be correlated. (C) 2004 Elsevier Ltd. All rights reserved.