The chemical states of ternary post-transition metal oxide thin films of InGaO, GaZnO and InZnO were investigated using X-ray photoelectron spectroscopy. Detailed binding energy (BE) analyses revealed certain evolution in chemistry in the ternary oxides compared to the reference binary oxides of In2O3, ZnO, or Ga2O3. In particular, O 1s BEs were changed with the compositions, which suggests that the charge transfer (CT) between In3+/Ga3+/Zn2+ and O2- ions is significant. Results of extended X-ray absorption fine structure analyses further showed that the first shell coordination (cation-O bond) is roughly maintained even though the ternary oxide films were structurally disordered. This implies that the CT process via O2- ions can influence the charge reconstructions in the ternary oxide systems. (C) 2015 Elsevier B.V. All rights reserved.