A series of alumina-supported vanadia catalysts with V2O5 loadings ranging from 3 to 20% were investigated by X-ray diffraction, V-51 solid State NMR, electron spin resonance, and oxygen chemisorption. V-51 NMR results under ambient conditions suggest that two types of vanadium oxide species are present on the surface : one due to a dispersed vanadia phase at lower V loadings and the other due to a crystalline vanadia phase at higher V loadings, Dispersion of vanadia was determined by the oxygen chemisorption method at 640 K and by a static method on the samples prereduced at the same temperature. At low loadings, i.e., below 9.8%, vanadium oxide is found to be present in a highly dispersed state, A comparison of the dispersion of vanadia determined by low-temperature oxygen chemisorption (samples reduced at 773 K for 6 h and subsequent oxygen chemisorption at 195 K) with that determined at 640 K shows that the latter method provides a better measure of the dispersion of vanadia. ESR spectra obtained under ambient conditions for the catalysts reduced at 640 K show the presence of V4+ ions in axial symmetry. The results are discussed in terms of the possible surface V species present on Al2O3.