Abstract XPS spectra of Fe 2O 3 and Al 2O 3 oxides are reported. The main emphasis is placed on the quantitative analysis of Ar + ion reductive effects on Fe 2O 3 surfaces in terms of n o/ n Fe atomic ratios achieved by use of the “First Principles Model”. No Fe metal is found in etched Fe 2O 3. Quantitative results show that the reduction: Fe 2O 3 → 2 FeO+ 1 2 O 2 occurs in the etching conditions used. Evidence of this reduction is found in the photoelectron spectra of the pure oxide as well as in those of Fe 2O 3+Al 2O 3 mixtures. A quantitative approach is proposed to derive Ar +-induced modifications at Fe 2O 3 surfaces in the mixtures. This approach permits the derivation of n o/ n Fe changes on the basis of intensity ratio measurements I O(Al)/ I O(Fe) between the two oxide components in the O 1s band of the mixtures. The correlation of derived n Al/ n Fe atomic ratios is very high in a vast range of composition of the mixtures analyzed either in the as received condition and in the etched condition. A sensitivity factor for the Fe 2p 3 2 transition is given: S Fe2p 3 2 = 2.50 (with respect to S F1s taken as the unity), which applies to the VG Esca 3 MkII apparatus used in this work. Comparison with previous quantitative XPS analysis of Fe 2O 3 and Al 2O 3 is presented.