Measured viscosities of mixtures of hexane and tetradecane are used to predict viscosities in three binary and one ternary system containing hexadecane. Predictions are based upon extrapolation, by means of the restricted congruence principle, of the excess Cibbs free energy of activation for flow. The errors in that function thereby range from 2.3 to 14.8 cal/mole for the several systems, and the corresponding errors in viscosity from 0.5 to 2.5%. Copyright © 1969 Canadian Society for Chemical Engineering