We compare the fundamental electric properties of Cu-poor and Cu-rich Cu(In,Ga)S-2 films before and after annealing, respectively. It has been found that the hole density of Cu-poor films increases after annealing in a O-2+S combined atmosphere, whereas annealing in S only does not produce a significant effect. We conclude that the oxygen is effective for the passivation of donor-type defects in the Cu-poor Cu(In,Ga)S-2 films. In the case of Cu-rich films, the hole density also increases with O-2+S-annealing. However, annealing in sulphur atmosphere (no oxygen gas) in this case has comparable consequences. These observations suggest fundamental differences in the incorporation mechanisms of oxygen and sulphur in both types of the film. A tentative model is presented, taking into account results from microstructural characterization of the films. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.