Determination of the precipitation onset in heavy crude oils is difficult due to their high viscosity. Dilution is one method utilized to enable this analysis. However, it is known that the asphaltenes phase behavior is a function of the type of molecule added to the oil, due to the changed composition. Therefore, the dilution should be done with a suitable solvent. Crude oil can be seen as a system of asphaltenes dispersed in the other components. In this work, these other components as a group are called the "Petroleum Media that Disperses the Asphaltenes'' (PMDA). A previously developed methodology was successfully applied to another type of crude oil, showing that the solubility parameter of the PMDA, and thus of the mixture of model solvents to be added to the oil without affecting the asphaltenes phase behavior, is different for each type of crude oil. The results obtained also show that obtaining a model system containing the model solvent mixture with solubility parameter equal to the oil's PMDA and the asphaltenes separated beforehand is only possible using the fraction of asphaltenes precipitated with alkanes as small as C1. (C) 2013 Elsevier Ltd. All rights reserved.