We propose a new model for the calculation of phase equilibria for the fluid mixtures based on the perturbed hard-sphere-chain (PHSC) equation of state. We modified the bonding term of the PHSC equation by introducing the form proposed by Chapman et al. The model predicts Monte Carlo simulation data for the compressibility factor better than those predicted by the PHSC equation in the entire density region. We can describe vapor/liquid equilibria of pure volatile saturated fluids with three characteristic parameters. By introducing two additional binary adjustable parameters, the liquid/liquid coexistence curve of a binary fluid mixture can be calculated. In the predictions of the specific volume of polymers, our model shows better agreement with the experimental data than predictions by the PHSC equation.