The oxidation state of alumina- and titania-supported Ru catalysts has been investigated as a function of reduction temperature, as well as by following the interaction with a methane-oxygen mixture at 773 and 973 K, employing XPS and FTIR techniques. It is found that the chemical behavior of Ru depends strongly on the material on which it is supported. Over Al2O3, ruthenium is incompletely reduced by treatment with hydrogen at 573 and 823 K, while oxidized Ru species are also detected following exposure of the catalyst to a methane-oxygen mixture at 773 and 973 K. In contrast, over TiO2, ruthenium is more easily reduced and is stabilized in its reduced state following hydrogen treatment at 823 K. During treatment with the methane-oxygen mixture, no reoxidation of Ru occurs. The interaction between Ru and TiO2, which inhibits the oxidation of ruthenium under conditions of partial oxidation of methane, is related to the unique ability of the Ru/TiO2 catalyst to promote the direct route of synthesis gas formation.