Equilibrium thickness of free thin films produced from aqueous solutions of C12(EO)5 surfactant (a model frother) with potassium ethylxanthate-KEX (a model collector) were studied in a wide range of concentrations (from 10-7 M to 2x10-2 M C12(EO)5; up to 10-2 M xanthate). The xanthate was found to behave similar to com_x001F__x001F_mon electrolytes and upon its addition the equilibrium film thickness was reduced, apparently due to the suppression of the electrostatic repulsion. However, at higher C12(EO)5 concentrations (>10-5 M ) the equilibrium thickness of the film increased relative to the thickness established with simple inorganic electrolytes at the same ionic strength. This was explained by the nega_x001F__x001F_tively charged xanthate interacting with the non-ionic frother at the interface and causing a build-up of charge. Higher frother concentrations were necessary to produce non-rupturing films upon increasing KEX content. This "antifoaming" effect of the xanthate compliments its influence on the electrostatic interactions in the film.