Methane mitigation, especially in the near-term, is critical for meeting global climate goals. The U.S. and China, as two of the largest global methane emitters, will play a significant role in global mitigation efforts through national methane emissions reduction, as well as by collaborating on key methane topics, as outlined in recent joint statements issued by both countries. Current methane emission estimates are highly uncertain, given that methane emission factors (i.e. the emissions intensity of different activities) are highly dependent on local conditions. This analysis evaluated around 50 estimates of methane emissions in the U.S. and China across all major sectors to identify areas of uncertainty and highlight opportunities for cross-country collaboration. Shared sources of emissions with high uncertainty include waste and livestock emissions, as well as abandoned fossil production sites (coal mines and oil wells), which present opportunities for knowledge sharing and joint leadership. Key areas for collaboration include improving data collection, monitoring and availability to develop more detailed emission factors that take into account local conditions and temporal sources of emissions. The U.S. and China can jointly collaborate on developing a transparent, multi-scale approach to emissions inventory development and mechanism for integrating multiple methodologies into national emissions estimates, to improve accuracy of emissions estimates and better inform mitigation strategies and policy discussions.