To mitigate fouling by asphaltenes, one must ensure that the asphaltenes remain soluble upon mixing of oils. The prediction of asphaltene solubility on the mixing of oils requires measuring the solubility blending number (solubility parameter) and insolubility number (asphaltene flocculation solubility parameter) of each component oil in the mixture. However, the measurement of the solubility blending number of an oil without asphaltenes by flocculation titration experiments using a solvent for asphaltenes, such as toluene, and a nonsolvent for asphaltenes, such as n-heptane, is not clear-cut. When flocculation titrations on blends of Athabasca vacuum gas oils with a nonideal reference oil that contains asphaltenes, Athabasca bitumen, were performed using existing test procedures, the results were inconsistent. Therefore, a new test method was developed to measure the solubility blending number of oils without asphaltenes by n-heptane titration of a series of blends with the reference oil and found to be consistent for both a nonideal reference oil, Athabasca bitumen, and an ideal reference oil, Arabian heavy crude oil.