The effect of non-absorbable gas on the heat and mass transfer for an absorption process taking place on a falling film flow in a porous medium is studied numerically. The liquid flow is modeled by the Brinkman-Forchhiemer extended Darcy equation. The solutions show that the non-absorbable gas has a strong effect in reducing mass absorption rate. The mass absorption rate increases with increasing solution flow rate, conductivity ratio and absorber pressure, and decreases with increasing porosity and the concentration of non-absorbable gas. An optimum conductivity ratio of 10 is observed while a minimum porosity of 0.9 is obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.