Reduction of the steam-to-carbon ratio in methane-to-synthesis gas reactions is a major concern in industrial research on natural gas conversion processes. A major obstacle is coke formation. In this work, comparative coke formation studies were performed in laboratory scale fixed and fluid bed reactors during methane-to-synthesis gas reactions. The catalytic tests were performed over a 0.15 wt.% Ni/Al2O3 catalyst with or without 1.7 wt.% La at 700-900degreesC and 1 atm with CH4:CO2:N-2 = 2:2: 1, CH4:O-2:N-2 = 2: 1:0 and CH4:02:1420 = 2:0.8:0.8. Catalyst samples were analysed for coke content and type by using temperature programmed oxidation. Only small amounts of coke were formed in the fluid bed reactor during steam-free catalytic partial oxidation. No coke was formed during a 114 h test at 800 degreesC in the CH4:O-2:H2O = 2:0.8:0.8 feed. Sequential tests indicated that even aged coke on the catalyst is easily gasified in the fluid bed reactor by adding oxygen to the feed. During CO2 reforming, similar coke amounts are formed in fixed and fluid bed reactors with similar gas compositions. However, coke formed in the fixed bed reactor has a higher oxidation temperature than coke formed in the fluid bed reactor after similar times on-stream. Finally, it was found that the La-promoter reduces the amount of coke formed on the catalyst, and also leads to a lower coke oxidation temperature.