Vapor-liquid equilibrium (VLE) data for binary systems of beta-pinene + p-cymene and beta-pinene + (S)-(-)-limonene and the ternary system beta-pinene + p-cymene + (S)-(-)-limonene were measured at 100.7 kPa using the modified Ellis equilibrium still. The experimental data of binary systems were tested for thermodynamic consistency with the method of Herington and point-to-point test of Van Ness. The parameters of four solution models-Wilson, nonrandom two-liquid (NRTL), universal quasichemical activity coefficient (UNIQUAC), and Liebermann-Fried-were calculated with the aid of the least-squares method to minimize an objective function based on the total pressure. The thermodynamic consistency of the VLE data of the ternary system was tested with the method of McDermott-Ellis, modified by Wisniak and Tamir. Also, the ternary system data were compared with the predicted values, using the parameters of Wilson model obtained from the binary systems. The predicted bubble-point temperature and the vapor composition for the ternary system were in good agreement with the experimental results.