The plasma in a cathodic arc evaporation process used for the deposition of Cr1-xOx films was studied by an optical emission spectroscopy (OES). With the introduction of Ar and oxygen into the chamber at deposition pressures from 0.7 Pa to 2.7 Pa, high density of evaporated chromium catalyzes the decomposition of oxygen reactive gas, and induces the formation of Cr1-xOx films. Optical emission spectra including atomic and ionized Cr, excited and ionized oxygen revealed that excitation, ionization and charge transfer reactions of the Cr-O plasma occurred during the Cr1-xOx deposition process. A simplified empirical model which incorporates the relevant atomic processes in the gas phase with the chemical composition and deposition rate of the deposited Cr1-xOx coating was developed. Rhombohedral Cr2O3 and tetragonal CrO2 were observed in the Cr1-xOx coatings deposited at higher pressure than 1.3 Pa. The Cr1-xOx coating depicted a dense and compact microstructure with well-attached interface. (c) 2007 Elsevier B.V. All rights reserved.