Tungsten oxide thin films have been prepared by reactive pulsed laser deposition (PLD). Substrate heat treatment and oxygen partial pressure during growth are correlated with Auger electron (AES), X-ray photoelectron (XPS), electron energy loss (EELS) and transmittance spectroscopies. Electronic and mass densities, composition and chemical states are strongly dependent of the deposition conditions. No significant change in the oxygen content in films as a function of substrate or annealing temperature is detected. However, the colored state turns out to be associated to the degree of chemical disorder in the samples, as evidenced by the peak shape of the W 4f transition. Also, the strength of a characteristic energy loss at 6-7 eV appears to be related to the presence of the colored state. (C) 2003 Elsevier B.V. All rights reserved.