The effects of surfactant contaminations and activated carbon addition on physical gas absorption, and absorption with fast and instantaneous reaction (sulphite oxidation, carbon dioxide absorption into sodium hydroxide and monoethanol amine (MEA) solutions) have been studied in a stirred cell with a flat gas/liquid interface. Surfactants significantly decrease the liquid-side mass transfer coefficient k(L) even at very small concentrations. The surfactants can be removed by adsorption onto activated carbon ("surfactant grazing"). In absorption with fast chemical reaction of the gas (sulphite oxidation), the liquid side mass transfer coefficient k(L) has no effect on the absorption rate and, consequently, there are no effects of surfactant and activated carbon. CO2 absorption into sodium hydroxide solution may occur in the instantaneous absorption regime; then, any change in k(L) causes a proportional change in the absorption rate. In CO2 absorption into MEA solution, however, in the instantaneous regime, much stronger effects of surfactant and of its removal by activated carbon are observed. It is suggested that in the absence of surfactants surface convection (Marangoni instability) may occur in MEA solutions. (C) 2007 Elsevier Ltd. All rights reserved.