The gas–liquid mass transfer coefficient was investigated in a novel multiphase reactor: the rotor–stator spinning disc reactor. Direct Numerical Simulations of the flow field around a single bubble in the reactor showed that vortex stretching invoked the presence of turbulence inside the thin liquid film surrounding the bubble. The Direct Numerical Simulations further provided a measure for the eddy diffusivity in the thin liquid film caused by this increase in vorticity. An expression was subsequently derived from a mass balance using these eddy diffusivities in order to estimate the order of magnitude of gas–liquid mass transfer coefficients. These estimates were found to lie more in line with experimental results in literature than previously used mass transfer models based on Higbie׳s penetration theory.