Chromium oxide was supported on different commercial aluminas. Their characteristics were assessed by different techniques (X-ray diffraction, X-ray photoelectron, laser Raman, and electron paramagnetic resonance spectroscopies, and Brunauer-Emmett-Teller surface, temperature-programmed reduction, and temperature-programmed desorption measurements). The variation of the Cr3+/Cr6+ ratio was accounted for by the interaction between the chromium phase and the support. The tendency of Cr3+ to form aggregates such as Cr2O3 was induced by the support. The features of the support exert-an influence upon chromium stabilization both in its oxidation states 6+ and 3+ and in the coordination of surface chromia species. The total acid sites and the oxidized chromium have a marked effect on activity and selectivity at initial operation times.