A free-energy model is developed for polymer chains in good solvents. This model, which combines the ideas of polymer field theory with liquid-state theory, is valid in the dilute, semidilute, and concentrated regimes. The model is compared against computer simulation data for the equation of state of tangent hard-sphere chain fluids. At low concentrations, it accurately describes the thermodynamics of tangent hard-sphere chains, reproducing the universal scaling behavior of long chains. At high concentrations, the model has an accuracy comparable to those of previous equations of state for tangent hard-sphere chains. [S0021-9606(00)51407-X].