This work shows that, when suitable theoretically based combining rules are used for the cross energy and cross co-volume parameters, cubic equations of state (EoS) with the van der Waals one-fluid mixing rules can adequately represent phase equilibria for the asymmetric CO2/hydrocarbon mixtures. These combining rules lead to semi-theoretical yet simple, meaningful and successful correlations for the interaction parameters K(ij) (of the cross-energy term) and l(ij) (of the cross co-volume term). Unlike previous correlations, the proposed equations relate the interaction parameters only to the pure component co-volume (b(i)) parameters, meaning that no additional properties (e.g. the critical volume), besides those required by the EoS itself (the critical temperature T(c), the critical pressure P(c) and the acentric factor) are used. Furthermore, the form of the correlations enables us to tune easily the cubic EoS when this is required for the prediction of phase behavior of petroleum fluids. A brief theoretical analysis on the temperature dependency of the K(ij) interaction parameter is also presented.