A vanadyl pyrophosphate catalyst, (VO)(2)P2O7, was investigated for its ability to selectively oxidize 16C(4) probe molecules, including hydrocarbons, alcohols, diols, and five-membered heterocycles, to maleic anhydride in a fixed bed microreactor. It was observed that besides linear-chain hydrocarbons and five-membered heterocycles previously studied, the butanols and butanediols can also be selectively oxidized into maleic anhydride. This demonstrates the existence of new selective oxidation pathways of organic molecules over the VPO catalysts. A novel cis-(su)peroxo-oxovanadium(V) dimeric active surface site is proposed for the (100) plane of (VO)(2)P2O7. New selective oxidation pathways of organic molecules over the (VO)(2)P2O7 catalyst involving the proposed active surface site are described. The proposed pathways are consistent with both the redox behavior of V-IV and V-V and the known organic chemistry of the C-4 probe molecules.