We study the influence of vertical high-frequency and small-amplitude vibrations on the separation of a binary mixture saturating a shallow horizontal porous layer heated from below. The monocellular flow obtained for a separation ratio psi > psi(mono) > 0 leads to a migration of the species towards the two vertical boundaries of the cell. The 2D direct numerical simulations and the linear stability analysis of the averaged governing equations show that the vertical vibrations delay the transition from monocellular flow to multicellular now. The vibrations also decrease the value of psi(mono), which allows species separation for a wide variety of binary Mixtures. (C) 2008 Elsevier Ltd. All rights reserved.