The placement of two Rushton disk turbines (DTs) in reactors for gas-liquid mass transfer has been studied in this work, and the correct position for each DT has been proposed. It is found that the volumetric mass transfer parameter k(L)a obtained with the correct placement of the two DTs can be substantially greater than that with the commonly adopted placement. The influence of the agitator positions on the correlation for k(L)a is also investigated, and it is shown that the dependence of k,a on power input is determined mainly by the upper DT position, while positions of both lower and upper DTs are important for the dependence of k(L)a on the superficial velocity.