Mass (or heat) transfer inside a spherical gas bubble rising through a stationary liquid is investigated by direct numerical simulation. Simulations were carried out for bubble Reynolds number ranging from 0.1 to 100 and for Peclet numbers ranging from Ito 2000. The study focuses on the effect of the bubble Reynolds number on both the interfacial transfer and the saturation time of the concentration inside the bubble. We show that the maximum velocity U-max at the bubble interface is the pertinent velocity to describe both internal and external transfers. The corresponding Sherwood (or Nusselt) numbers and the saturation time can be described by a sigmoid function depending on the Peclet number Pe(max) = U(max)d(b)/D (d(b) and D being the bubble diameter and the corresponding diffusion coefficient). (C) 2013 Elsevier Ltd. All rights reserved.