Gas absorption and pressure drop were studied in a fin-wall conduit; a fin-wall conduit is a rectangular duct with fins placed on two internal walls perpendicular to the axis of flow. Pressure drop data were obtained with the air-water system. Gas absorption data were obtained with the air-ammonia-water system, and were corrected for the expected liquid-phase resistance by the use of oxygen desorption data. The pressure drop per transfer unit is on the order of 0.05 in. of water per transfer unit.