Biomethanation of syngas offers a sustainable route for renewable methane production. However, CO-rich gas streams pose challenges due to microbial inhibition. This study evaluated a thermophilic trickle bed reactor (TBR) operating for 180 days with mixed microbial cultures and varying syngas compositions. Peak methane production of 6.8 Nml/ml·d and high elimination capacities of 85% H₂, 60% CO, 99% CO₂ were achieved during syngas feeding, while CO-only phases showed reduced performance. The findings highlight TBR as a viable system for syngas upgrading and provide insight into optimizing CO biomethanation.