We apply conformal solution theory and extend to mixtures a recently derived equation of state for glass-forming liquids. The equation of state is based on the statistical properties of the multidimensional potential energy surface as a function of a macroscopic system's degrees of freedom (energy landscape), and allows the calculation of an ideal glass transition locus, along which the configurational entropy vanishes. The landscape mixing approach yields an expression for the composition dependence of the mixture's glass transition. A non-monotonic composition dependence is predicted by the theory for the glass transition of a binary Lennard-Jones mixture. The composition dependence of species diffusivities obtained by molecular dynamics simulation of this mixture is consistent with the theoretical prediction. (c) 2005 Elsevier B.V. All rights reserved.