Effects of aiding and opposing flows on buoyancy-induced convection in a vertical porous annulus have been numerically investigated. A finite heat source is located on the inner wall of the annulus which is otherwise adiabatic, and the outer wall is cooled at a constant temperature. Isothermal and constant-flux heat sources have been considered. Calculations cover a wide range of Rayleigh and Peclet numbers (10 ≤ Ra ≤ 100, and 0 ≤ Pe ≤ 100) for various radius ratios, 0 ≤ γ ≤ 10. For the present study, heat transfer results for mixed convection can be best presented in terms of two parameters Nu/Pe 1/2 · and Ra/Pe for the isothermal source and Nu/Pe 1/2 and Ra/Pe 2 for the constant flux heat source.