Experimental liquid-liquid equilibrium data for the ternary mixtures water + methanol + isoamyl acetate and water + ethanol + isoamyl acetate at various temperatures are reported, together with the results of correlation by the original UNIQUAC equation using both structural parameters q and r from the literature and q’s and r’s optimized for each mixture as part of the overall correlation procedure. The improved fit obtained with the optimized parameters (which differed from the "universal" values only for the smaller molecules) may be viewed as being due to the active surface area and volume of a molecule being dependent upon its environment.