Abstract
A linear stability analysis is applied to a system consisting of three horizontal layers, a viscous fluid layer sandwiched between two porous medium permeated by the fluid that the lower layer is heated uniformlly from below. Flow in the porous medium is assumed to be governed by Darcy's law. The Beavers-Joseph condition is applied at the interface between any two different layers.Spectral method of Chebysheve polynomials are used to obtain numerical solution for stationary convection and overstability cases.