Mass fractions at the end of the core O-burning from one-zone calculations based on central conditions of a 15 M_⊙ star with and without rotation, shown for three nuclear rate references (colour-coded). The dashed grey line shows the abundances at the end of the core C-burning from the one-zone calculation of the non-rotating CF88 model, while the solid grey line indicates the initial composition at the onset of core C-burning. Lower panels display the abundances normalised to those of the non-rotating CF88 case.