Mass transfer efficiency η (colour coded) during fast (top panels) and slow (middle panels) Case A, and during Case AB (bottom panels) as function of initial orbital period and initial mass ratio, for systems with initial donor masses of ∼16 M_⊙ and ∼40 M_⊙ in the left and right panels, respectively. Each coloured square represents one binary evolution model, with the colour denoting the mass transfer efficiency. Black frames around coloured square indicate models that has undergone a contact phase lasting more than three thermal timescales of the mass donor.