The phase equilibrium, density, and viscosity of CH4, C2H6, and CO2 with high n-alkane systems are of particular importance in various industrial processes and design. The binary interaction coefficients (k(ij)) of these systems for the simplified Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFF) modeling were studied systematically. A new k(ij) correlation on temperature and molecular weight was proposed to compensate the deviations as the simplified PC-SAFT averages the temperature- and molecular weight-dependent segment diameters of the original PC-SAFE The average absolute relative deviations in pressure by the new correlation was only 3.6% for more than 2000 vapor-liquid equilibrium data, covering 49 binary systems of CH4, C2H6, and CO2 with n-alkanes up to n-C44H90. In addition, the prediction ability of the new correlation was verified by predicting the phase equilibrium and saturated density and viscosity of various high asymmetric systems. The new correlation has increased the prediction accuracy of the simplified PC-SAFT. (C) 2015 Elsevier B.V. All rights reserved.