Catalyst supports are known not to be inert, but react with some gases, such as sulfur species. Understanding the interaction of sulfur species with the supports is necessary to design improved catalysts or optimize regeneration protocols. We investigated the oxidation state of sulfur on supported Ru catalysts and blank supports during methanation, sulfur poisoning, oxidative regeneration, and subsequent reacitvation by sulfur K-edge X-ray absorption spectroscopy (XAS). We found that oxide (Al2O3 and ZrO2) supported Ru forms sulfides on the Ru and sulfates on the support during poisoning. Upon regeneration, sulfur is transported from the Ru to the support, and is transported back upon subsequent reducing conditions, impeding complete regeneration. On C-supported Ru, not all sulfur is removed by oxidation, making regeneration by oxidation under the tested conditions impossible. (C) 2013 Elsevier B.V. All rights reserved.