This paper describes the effect of surfactant (0.025%w/w octanol) on mass transfer of oxygen into water-glycerol solutions of viscosity up to 21 mPa s in a pulsed baffled reactor. We also report the effect of air entrainment on the volumetric mass transfer coefficient in the open reactor system. The results show that the presence of octanol in solutions increases the mass transfer rate for all the experimental conditions tested, in particular, a higher percentage increase in k(L)a was obtained for more viscous solutions. This behaviour can be attributed to the non-coalescing characteristics of the octanol that is added to the water-glycerol solutions. The results of air entrainment on k(L)a suggest that the effect of the surface air entrained into the system on k(L)a measurement is insignificant.