Coke deposition on reforming reaction catalysts, typically Ni particles deposited on alumina supports, has been a major obstacle barring their practical industrial application. In this work, a Ni/gamma-Al2O3 catalyst was stabilized by a pretreatment with steam at high temperature of 850 degrees C. The steam-treated Ni/gamma-Al2O3 catalyst showed thermodynamically possible highest conversion (98.3% for methane and 82.4% for carbon dioxide) and H-2/CO ratio of 2.01 for combined steam and carbon dioxide reforming of methane, and operated stably for 200 h. The amount of deposited carbon coke was 3.6% for steam-treated catalysts whereas conventional catalysts had 15.4% of coke after 200 h of the reaction. The steam pretreatment removed unstable aluminum that can otherwise leach out, which causes severe carbon deposition at the early stage of the reaction. This novel steam pretreatment enhanced the carbon resistance of the catalysts significantly, resulting in improved activity and long-term stability. (C) 2013 Elsevier B.V. All rights reserved.