In view of various contradictory theoretical equations relating the interfacial tension sigma between phase-separated polymer solutions to the Flory-Huggins interaction parameter of the system, the idea that sigma should depend on the extent of the ’hump’ in the concentration dependence of the Gibbs energy of mixing was studied. This investigation is based on 12 series of sigma(T) measurements reported in the literature and on additional experiments for the system cyclohexane/polystyrene. To quantify the extent of the ’hump’, a reduced ’hump energy’ epsilon was introduced and its value calculated for different temperatures from the measured critical data of the systems. The analysis of the entire experimental material yields a scaling law of the form sigma = E epsilon(F) where F is close to 0.5 for all systems, in contrast to E which varies within a larger interval. Furthermore, epsilon is related to tau, the relative distance to the critical temperature, by epsilon = A tau(B); B is approximately 2.4, again relatively independent of the system, in contrast to A. In case of trustworthy values of the scaling parameters, the above relations offer an interesting possibility to estimate sigma(T) from the sole knowledge of the critical temperature of the system.