The mixed convection boundary-layer flow on one face of a semi-infinite vertical surface embedded in a fluid-saturated porous medium is considered when the other face is taken to be in contact with a hot or cooled fluid maintaining that surface at a constant temperature . The governing system of partial differential equations is transformed into a system of ordinary differential equations through an appropriate similarity transformation. These equations are solved numerically in terms of a dimensionless mixed convection parameter and a surface heat transfer parameter . The results indicate that dual solutions exist for opposing flow, , with the dependence of the critical values on being determined, whereas for the assisting flow , the solution is unique. Limiting asymptotic forms for both small and large and large are also discussed.