For the design and scale-up of gas-liquid ejectors, reliable data are required which describe the mass transfer characteristics as a function of the physical fluid properties, geometrical design and the process related parameters. Therefore, the mass transfer characteristics of various ejector geometries and scales were investigated using the desorption of oxygen from water, by means of an inert gas, as a model system. In order to investigate scale-up, the ejector was geometrically scaled-up by a factor of 2 (and hence, a volumetric scale-up by a factor of 8). Since industrial venturi reactors are operated at elevated pressures, the influence of the gas density on the mass transfer characteristics was also studied. The experimental results show that geometrical design parameters, like the presence of a swirl device in the upstream section of the nozzle, the mixing tube length and the nozzle to mixing tube diameter ratio, all influence the mass transfer characteristics significantly. Further, it was experimentally verified that the gas density influenced the mass transfer characteristics. It was observed that the volumetric mass transfer coefficient (k(L)a) increases when higher density gases are used. The main objective of this study is investigating the influence of the ejector geometry on the mass transfer characteristics of gas-liquid ejectors and to formulate design and scale-up rules/criteria.