Vapor-Liquid Equilibrium (VLE) calculations have been made on binary and ternary azeotropic mixtures using the Peng-Robinson equation of state (EOS). Various mixing rules of the van der Waals one-fluid model, the local composition model and the group-contribution model for the VLE computations were discussed. In the group-contribution model, we applied the Huron-Vidal method and determined the EOS parameters for mixtures from the UNIFAC activity coefficient model. This study compares the phase equilibrium calculations and investigats the prediction of azeotropic properties. It was shown that the group-contribution mixing model yielded satisfactory results, and provided a superior calculation method to other mixing rules or correlation equations.