This paper discusses the evaluation of the structural integrals which weight the contribution of various attraction pair potentials to mixture properties. These integrals are generated when pairwise attraction in a mixture is considered to be a first order perturbation on a mixture of nonattracting hard spheres. For pure components these integrals have the form ~ y2-ngnS(y, pd 3) dy, where gHS is the pair distribution function for pure hard spheres of diameter d and y is the ratio rid. This paper shows that the corresponding integral for the first order perturbation contribution of an i-j pair in a mixture can be evaluated to within about 3 per cent of its computer simulation value by means of an approximation given by ~ y2-ngnS(y, p(d3)) dy. In this approximation, the (d 3) term is a composition dependent average of the diameters of all constituents of the mixture, gnS is the pair distribution function for pure hard spheres with the pair interaction diameter di, , and y is the ratio rid 0. The form of the composition dependence of (d ~) is determined by a solution of the Ornstein Zernike equation for a pair in a mixture of hard spheres.