The excess activation free energy of flow as defined in the Eyring model was calculated from the excess Gibbs free energy of mixture multiplied by a proportionality factor, in which the excess Gibbs free energy of mixture was estimated from the Patel-Teja equation of state with zero binary interaction constant. It was found that the proportionality factor could be treated as a constant for a nonaqueous system, whereas the factor was considered as a linear composition-dependent (LCD) function for an aqueous system (or a strongly hydrogen-bonded system). Promising results have been obtained from the proposed method to correlate viscosity data for a wide variety of nonaqueous and aqueous mixtures. These model parameters could be estimated from a limited knowledge of mixture viscosity data; one point for a nonaqueous system and two data points for an aqueous system.