Phase behavior of (bitumen + solvent) mixtures and their properties are essential for surface upgrading methods and enhanced oil recovery applications. The objective for this work is to systematically model the phase partitioning and component distribution in the (bitumen + solvent) mixtures. To perform equation of state modelling, compositional analysis of bitumen is utilized to characterize the bitumen sample and its components up to C-100. The full range of components is utilized in Peng-Robinson equation of state (PR-EOS) to predict the equilibrium phase properties, such as composition and density, in vapor-liquid and liquid-liquid regions. Based on the results, PR-EOS accurately captures the composition of phases, component distribution in each phase, and phase densities. Thereafter, an algorithm is proposed to lump the components on the basis of two-phase envelope generation. The results indicate that Athabasca bitumen and its phase behavior in (bitumen + solvent) mixtures can be well represented in multi-phase regions by four pseudo-components.