There are a large number of correlations given in literature for the prediction of volume-related liquid-side mass transfer coefficients in mechanically agitated gas-liquid contactors. Significant disagreement can be observed concerning the proposed correlations, so that no single correlation exists representing all of the mass transfer data given in the literature. The observed differences can mainly be ascribed to the differences in the geometry of the system, the range of operational conditions and the measurement method used. On the basis of a comparative study of mass transfer phenomena in agitated Newtonian and non-Newtonian aerated liquids, a critical discussion of the literature results is presented in this review article, so that final conclusions can be drawn for the k(L)a values in the different single- and multiple-impeller agitated systems studied in the literature.