It was found that transport properties of gases (viscosity eta, thermal conductivity lambda, and diffusion coefficients D) in the form of the quantity: C = etaD/lambdaT(alpha) are temperature independent in the 700-2000 K temperature interval. Although the exponent alpha seems to be independent inside the group for all the monoatomic vapours it seems to change between different groups (alpha = 1.909 +/- 0.015 for alkali metal vapours - Li, Na, K, Rb and Cs: alpha = 1.72 +/- 0.05 for noble gases - He, Ne, Ar, Kr, and Xe). In this approach, transport properties of gases are correlated using only different values of C. This fact was extended to the properties of the binary mixtures of monoatomic and diatomic molecules in the alkali metal vapours, to obtain the mutual diffusion coefficients D-12(T, p) and the self-diffusion coefficients of diatomic molecules, D-22(T). (C) 2004 Elsevier B.V. All rights reserved.