The interfacial tensions of pure fluids and binary fluid mixtures are described following an investigation of phase behavior. A modified version of the perturbed hard sphere chain (PHSC) equation of state (PHSC-CL EOS) is developed by applying the chain length dependence contribution to the PHSC EOS. The density gradient theory (DGT) is combined with the proposed model to account for both the phase equilibria and the interfacial tension. The influence parameter, the only input of the DGT with EOS to calculate the interfacial tension of the fluid, is considered an adjustable parameter for each fluid. The PHSC-CL EOS accurately describes the vapor liquid equilibria (VLE) and interfacial tensions of fluids away from the critical region. It is combined with a renormalization group theory to consider the contribution of long range fluctuations in the near critical region. The calculation procedure is based on White's work and the phase space cell approximation is adopted for mixtures. The VLE and interfacial tensions are obtained with good agreement to experimental data for linear alkanes, cyclo hexane, benzene, toluene, carbon dioxide, and their binary mixtures. (C) 2016 Elsevier B.V. All rights reserved.