Efficiency of mass transfer in a ﹩16\;{{\rm{M}}}_{\odot }+15\;{{\rm{M}}}_{\odot }﹩ binary system including differential rotation. The system is modeled with tides as described by Hurley et al. (2002) for radiative envelopes, and also with the simple tidal timescale given by Zahn (1977). The upper panel shows the efficiency of mass transfer, the middle panel the angular frequency of each star in terms of its critical value, while the lower panel shows the evolution of ﹩\dot{M}﹩ for both components.