The structure and surface composition of binary oxides consisting of CrOx and VOx dispersed on alumina and their effects on the rate and selectivity of oxidative dehydrogenation (ODH) of propane were examined and compared with those for CrOx and VOx dispersed on alumina. VOx deposition on an equivalent CrOx monolayer on alumina and deposition of CrOx on an equivalent monolayer of VOx deposited on alumina led to CrVO4 species during thermal treatment with concomitant reduction of Cr6+ to Cr3+. Autoreduction of Cr6+ to Cr3+ is also detected for CrOx, even without the presence of VOx. Infrared spectroscopy of NO adsorbed at 153 K probes the relative abundance of alumina and of V5+, Cr3+, and Cr6+ at surfaces. This technique detects differences in the surface composition of VOx/CrOx/Al2O3 and CrOx/VOx/Al2O3. The first of these samples is enriched in VOx relative to CrOx compared with the second sample. Consistent with this finding, VOx/CrOx/Al2O3 and CrOx/VOx/Al2O3 are distinguishable in their ODH activities and propene selectivities. The highest ODH activity and propene selectivity is observed for VOx/CrOx/Al2O3, which exhibits a surface enriched in VOx and having a low surface concentration of Cr6+.