The Hildebrand fluidity equation [Φ = B( V̄ - V̄0)V̄0] has been applied to simple binary and ternary systems, using the following mixing rules: V̄ = σiXiV̄l°, V̄0 = σXiV̄0i, BV̄ = (B1V̄1°)v1 (B2V̄2°)v2⋯ in which V̄i° is the molar volume of a pure liquid, V̄0i is the limiting molar volume of a pure liquid, and v, is a volume fraction. These mixing rules allow prediction of the viscosities of mixtures from the properties of the pure liquids, with a maximum deviation of 10% in the 11 binary and 2 ternary systems considered. These predictions are shown to be comparable to, or better than, the best predictions of four commonly used “zero parameter” equations for viscosities of mixtures.