Abstract The interaction parameter X has been defined as a measure of the chemical potential of the solvent in solutions with a polymeric solute. Consequently a number of equilibrium properties can be expressed as functions of X. Values of X determined from these properties reveal that for most systems this quantity increases with the volume fraction of polymer in the solution. Accordingly, values of the interaction parameter have been tabulated as a function of concentration, as well as of temperature. The values of X obtained either from experiment or theory can be utilized for predicting the colligative properties and determining the solubility characteristics of polymer-solvent systems.