  The mass transfer efficiency during the evolution of massive binaries is
still uncertain. We model the mass transfer processes in a grid of binaries to
investigate the formation of Wolf-Rayet+O (WR+O) binaries, taking into account
two kinds of non-conservative mass transfer models: Model I with
rotation-dependent mass accretion and Model II of half mass accretion.
Generally the mass transfer in Model I is more inefficient, with the average
efficiency in a range of $\sim0.2-0.7$ and $ \lesssim0.2 $ for Case A and Case
B mass transfer, respectively. We present the parameter distributions for the
descendant WR+O binaries. By comparing the modeled stellar mass distribution
with the observed Galactic WR+O binaries, we find that highly non-conservative
mass transfer is required.
