Different catalytic oxidation effects of Ce on W(110) and W(111) were observed with photo- emission spectroscopy. On Ce-covered W(110), the top W layer is quickly oxidized to a surface monoxide at room temperature. Oxidation is almost halted after the completion of one monolayer of WO. On Ce/W(111), instead of WO, WO3 grows on the surface under the same conditions. The monolayer suboxide formation found on Ce/W(110) and Ce/Ta(110) (as reported earlier) is a direct consequence of the most densely packed structure of the bcc (110) surfaces. The more effective oxidation promotion on the W(111) surface is attributed to its open structure. The mechanism of Ce-catalyzed oxidation is further tested in this study.