Asphaltene precipitation from oils depends on the composition of solvent components such as resins and aromatics. Fouling of asphaltenes from a heavy oil in mixtures of fuel oil and de-asphalted vacuum bottoms was studied at asphaltene concentrations of 0.04 − 3.36 %, and resin concentrations of 3.1 − 4.9 %. Fluids under nitrogen were recirculated at 85°C through an annular test section with initial surface temperature of 230°C for periods up to 30 hours, and the fouling monitored by thermal measurement. The effects of concentration of heavy oil and de-asphalted oil are explored. Fouling rates are correlated with the ratio of resins / asphaltenes.