The Government of Japan and many other governments seek achieving carbon neutrality to avoid dangerous climate change. Hydrogen and synthetic gas (methanation) are focused as zero-emission options in gaseous fuel. Methanation is a process for synthesizing methane produced by zero emission hydrogen and CO2 captured from flue gases, but particularly methanation has not been analyzed enough in terms of the conditions of economic feasibility and economical potentials. This study evaluated contributions of methanation as well as hydrogen for global carbon neutrality, using a global energy systems model. According to the analysis, methanation is one of the important roles for the deep emission reductions toward carbon neutrality in the world. Amounts of global exports and imports of the synthetic gas (methanation) will be almost same as those of hydrogen in 2050. Particularly in Japan, the role of methanation option will be big among the world nations. Without the methanation option, the global emission reduction costs for achieving 2 ℃ target will increase by about 14 billion US$/yr in 2050.