Velocity cross-correlation coefficients (VCC's) may be used as measures of the coupling between the velocities of different molecules in binary liquid mixtures. The hydrodynamic expression for the VCC's proposed by Friedman and Mills is used to derive expressions for the VCC's in terms of molecular diameters and the Kirkwood-Buff parameters. The main approximation is the use of the Ornstein-Zemike form for the liquid radial distribution functions supplemented by a small separation cutoff. An ideal reference system for the VCC's is proposed in terms of hypothetical ideal Kirkwood-Buff parameters. Experimental VCC's, experimental Kirkwood-Buff parameters, theoretical VCC's using our expression, and reference VCC's are computed from literature data for eight binary liquid systems ranging from nearly thermodynamically ideal to very nonideal. Good agreement is shown between the experimental and predicted VCC's over the entire composition range of these mixtures.
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