Catalytic compositions of oxides of titanium, vanadium and tin that are suitable for the production of phthalic anhydride by oxidizing o-xylene and/or naphthalene in the gas phase. The catalysts exhibit excellent activity and selectivity. The catalyst contains 2 to 15 percent by weight (calculated as V.sub.2O.sub.5) of vanadium, 1 to 15 percent weight (calculated as SnO.sub.2) of tin and 70 to 97 percent by weight (calculated as TiO.sub.2) of titanium. In a preferred embodiment the catalyst also contains up to 5 percent by weight (calculated as M.sub.2O) of at least one alkali metal, preferably lithium, potassium or rubidium, and more preferably cesium. In an even more preferred embodiment, cesium is present in an amount of from 0.01 to 2 percent by weight (calculated as Cs.sub.2O).
