Methane (CH₄) emissions were measured in the megacity of Osaka, Japan, using mobile and eddy covariance methods. The CH₄ emissions were much higher than those reported in local inventories, with natural gas contributing up to 74 % of the emissions. Several CH₄ sources not accounted for in current inventories were identified. These results emphasize the need for more comprehensive emissions tracking in urban areas to enhance climate change mitigation efforts.