The binary cross second virial coefficient in the mixing rule of Wong and Sandler (1992) can be determined analytically from pure component parameters and activity coefficients at infinite dilution. The modification allows to determine the binary interaction parameter without the additional minimization of excess Gibbs energy deviations. At low pressures, the accuracy of the modification is comparable to that of the original model. High pressure phase equilibria were predicted by the modification of the Wong-Sandler mixing rule with Modified UNIFAC and ASOG group contribution methods.