A perturbed hard-sphere-chain (PHSC) equation of state is presented which uses the modified Chiew equation of state for hard-sphere chains as the reference term, a van der Waals type perturbation term, and the Song-Mason method to relate equation-of-state parameters to the intermolecular potential. The PHSC equation requires three parameters to describe a pure fluid : the number of effective hard spheres per molecule, the segmental diameter, and the intermolecular potential-well depth between a nonbonded pair of segments. The PHSC equation reproduces the thermodynamic properties of a wide variety of normal fluids including polymers. Regressed parameters are related to characteristic molecular properties calculated from group contributions based on chemical structure.