The heavy-RPG(Raw Pyrolysis Gasoline), which is a variable mixture of mainly unsaturated C₉ fractions in the cracking of petroleum naphthas, is one of the important feed materials for petroleum resins. To produce the resin with favorable quality, one need to use well purified fraction of the h-RPG and, accordingly, a knowledge of the phase equilibria for the h-RPG is required. The h-RPG, however, is regraded as a typical continuous mixture which contains far too many components for standard chemical analysis. Thus, we present here an efficient method collecting phase equilibrium data for such a mixture based the method of continuous thermodynamics and the Peng-Robinson equation of state. First, through the gas chromatographic analysis and the ASTM D86 experiment for a typical h-RPG mixture, we identified the total number of 43 constituents and found the distribution of TBPs. Then, the continuous fraction of h-RPG mixture is characterized by gamma function where the TBP index is used as the distribution variable. Finally, we performed bubble and dew point, and flash calculations by the quadrature method to the continuous fraction. The results are compared with those calculated by the pseudo-component methods. We found that the method presented here can be used for the reliable phase equilibrium calculation of such a continuous mixture while significantly reduce the computation time with more favorable accuracy over the conventional pseudocomponent method.