An equation of state for square-well chain fluids is developed applying the second-order perturbation theory of Barker and Henderson to a hard-chain reference fluid. The structural information required in the perturbation theory is incorporated using an expression for the radial distribution function of the reference chain fluid proposed by Chiew. The equation of state is simplified by fitting polynomials in density and simple functions of segment number to the original perturbation expressions of first-and second-order. The equation of state is extended to mixtures by applying one-fluid mixing rules and is tested against molecular simulation data of homonuclear chain molecules and mixtures from the literature.