The effect of surfactant (0.025 wt% octanol) on mass transfer of oxygen in a bubble column containing 1 wt% aqueous CMC was studied. The presence of octanol in solution increased the total mass transfer by 50%. Gas hold-up measurements indicated a tri-modal bubble size distribution, comprising (1) large fast forming slug bubbles, (2) bubbles of about 5 mm diameter and (3) 1 mm bubbles. Their respective contributions to mass transfer were (1) 25-40%, (2) 30-45% and (3) 30%. With regard to the oxygen transfer, as a proportion of the maximum transfer possible the respective proportions were (1) small, (2) about 50% and (3) near 100%; thus for the smallest bubbles the exit gas was nearly in equilibrium with the liquid.