A numerical study has been conducted to investigate the mass transfer inside a spherical bubble at low to moderate Reynolds numbers. The Navier-Stokes and diffusion-convection equations were solved numerically by a finite difference method. The effect of the bubble Schmidt number (over the range 0.1 < S-cd < 5) and of the internal Reynolds number (over the range 0.1 < R-ed < 13) on mass transfer is investigated. The results show that the mass transfer is strongly dependent on the Reynolds number and the Schmidt number. From the numerical results, a predictive equation for the Sherwood number in terms of the Schmidt number and the Reynolds number is derived. (C) 2016 Elsevier Ltd. All rights reserved.