We calculate the shape of the 2p core level photoemission spectrum for Cu2O, CuO and NaCuO2, where Cu is formally mono-, di- and trivalent, respectively. Although the number of 3d electrons is similar in the three compounds, there is a large variation in the strength of the d9-like satellite and in the width of the main line. We relate the differences between Cu2O and CuO to the difference in the valence, while for NaCuO2 the detailed form of the hopping matrix elements is also found to be important. © 1992 IOP Publishing Ltd.