Application of an approach recently published [Carreon-Calderon et al. Ind. Eng. Chem. Res. 2012, 51, 14188-14198] to heavy petroleum fluids allows calculation of critical properties and molecular pseudostructures of their undefined fractions. This approach is based on group contribution methods, where classical thermodynamics is used as framework to assign functional groups to each undefined fraction by minimizing its free energy. The calculated properties are employed to determine parameters entering into cubic equations of state and their respective mixing rules requiring molecular structures. Thus, phase equilibrium simulations of heavy petroleum fluids were performed employing neither specific correlations nor parameters, reducing the impact of fluid models over the thermodynamic characterization. The results are in agreement with experimental results of petroleum fluids heavier than 14 degrees API.