New mixing rules which are general and easy to use have been developed to predict the properties of mixtures from the BWR equation. The rules contain a binary interaction parameter, readily obtainable from the experimental values of the second virial cross-coefficients. The mixing rules were used to predict the densities of binary mixtures of carbon dioxide with methane, ethane and propane at elevated pressures. For any of the three mixtures, the standard error of the predictions was approximately equal to or less than the sum of the standard errors of fit for the pure components. The BWR parameters for the pure components, required in the above predictions, were determined by minimizing the sum of relative error squares in specific volume. Copyright © 1972 Canadian Society for Chemical Engineering