Zinc-modified, gamma-Al2O3 supported vanadium oxides were prepared by dry impregnation and co-precipitation methods. The solids were characterized by X-ray diffraction, UV-VIS, V-51 NMR and X-ray photoelectron spectroscopy and compared as catalysts in propane oxidative dehydrogenation (ODH). It was shown that only true co-precipitation methods lead to interaction of amorphous zinc vanadates with the surface of alumina. Selectivity spectra in propane ODH were used as a fingerprint to characterize superficial vanadates. (C) 2002 Elsevier Science B.V. All rights reserved.