The variation with photon energy in the Cu L 2,3-M 4,5M 4,5 Auger-electron spectroscopy (AES) (satellite/main line) spectral intensity ratio is analyzed for Cu metal and CuO. It is shown that the variation in the branching ratio of the Auger (or Coster–Kronig (CK)) decay width with the number of the spectator M 4,5 hole has to be explicitly taken into account in the analysis. Otherwise, the analysis cannot explain well the variation with photon energy in the AES (satellite/main line) spectral intensity ratio. The branching ratios are determined. They vary fairly significantly with the number of the spectator hole. The L 2M 4,5-L 3M 4,5M 4,5 CK decay width of CuO becomes almost twice as large as the L 2-L 3M 4,5 one. This is in accord with the variation in the CK decay width with the CK final-state potential. We discussed also why the Cu L α X-ray emission spectroscopy main line width of CuO is much narrower than the Cu L 3 photoelectron spectroscopy main line width.