In an earlier study

we proposed a new method in which the surface tensionsof mixtures of organic non-electrolytes are predicted successfully by the well-kn own UNIFAC group contribution method used in phase equilibrium calculations. In this paper

four different molar surface area equations are investigated with respect to precision of surface tension prediction by the use of our proposed method of applying UNIFAC model. Different molar surface area equations are given as: Ai=Ai = ViB2/3NA1/3 (1) Ai=Ai = 1.21ViB2/3NA1/3 (2) Ai=Ai = ViB4/15Vic2/5NA1/3 (3) Ai=Ai = 1.21ViB4/15Vic2/5NA1/3 (4) where Ai and Ai are the molar surface area and the partial molar surface area of component i respectively

ViB is the liquid molar volume of pure component i

NA is Avogadros number

and Vic is the critical molar volume of component i. The surface tensions of 100 binary

10 ternary and 2 quaternary systems are calculated with the above equations. Comparing calculated values vith experimental data

we conclude that equation(4) is the best for the systems containing both water and alcohols. The total average relative deviations from experiment are 6.98% for 6 systems containing both water and alcohols. These results are satisfactory for engineering design.