The rate of absorption from a multicomponent gaseous mixture into a flowing stream in the presence of instantaneous surface reaction is investigated. This is effected by using the generalized Fick's Law for multicomponent diffusion and also by applying the approximate approach based on the assumption that the concentrations of the reactive species are small. Constant properties are assumed for the mixture which are taken at a reference state. As an example, the absorption of C02-H2S and C02-H2 from air are considered. The results show that when the binary diffusion coefficients of the species in the inert gas are greatly different, the error introduced in calculations based on the "Low Concentration" approach is quite appreciable.