Mass-based mixing rules are proposed for the Expanded Fluid viscosity correlation that are suitable for asymmetric mixtures and replace the original volumetric mixing rules. The Expanded Fluid correlation provides viscosity values as a function Of. : fluid density and characterizes each pure compound with three fluid specific parameters : c(2), rho(o)(s) and c(3), when using experimental densities and two parameters, c(2), rho(o)(s), when using a cubic equation of state. The proposed set of mixing rules predicts the viscosity of over 90 binary mixtures with Overall. average absolute relative deviations (AARD) of 2.9% and 7.8% Using Measured densities and densities estimated from an equation of state, respectively. To improve the predictions in equation of state applications, a binary interaction parameter is introduced to the mixing rules, compensating for inaccuracies associated with density predictions from simple Cubic equations of state. Using fitted interaction parameters, the overall AARD is 3.6%. The binary interaction parameters are generalized as a function of the molecular weight and Watson K-factor. Using these generalized binary, interaction parameters, the overall AARD reduced to 5.4% for over 90 binary mixtures.' The proposed mixing rules and :general binary interaction :Parameters correlations are also tested on an independent data set which includes 40 binary, ternary, and multicomponent mixtures. The overall AARDs are 8.4% using measured densities and, 11.6 and 7.1% using equation-of-state based densities with Zero and generalized binary interaction parameters, respectively.