Carbon dioxide reforming of methane was performed over a commercial nickel-based catalyst(ICI 46-1) to compare it with steam reforming of methane. Under the same conditions, the conversion of methane in carbon dioxide reforming was lower than that in steam reforming, but the yield of carbon monoxide was higher due to the higher selectivity to carbon monoxide. While no deactivation of catalyst was observed in steam reforming, cokes, which can be formed by methane cracking(CH₄→C+2H₂) or Boudouard reaction(2CO→C+CO₂), deactivated the catalyst for carbon dioxide reforming. Carbon dioxide reforming produced synthesis gas with a low hydrogen-to-carbon monoxide ratio, which could be useful for synthesis reactions requiring such a ratio. No synergy effect between carbon dioxide and steam was found for simultaneous carbon dioxide and steam reforming of methane.