The catalytic partial oxidation of methane with oxygen to produce synthesis gas was studied under a wide range of conditions over supported ruthenium catalysts. The microreactor results demonstrated the high activity of ruthenium catalysts for this reaction. A catalyst having as little as 0.015% (w/w) Ru on Al2O3 gave a higher synthesis gas selectivity than a catalyst having 5% Ni on SiO2. XANES measurements for fresh and used catalyst samples confirmed that ruthenium is reduced from ruthenium dioxide to ruthenium metal early during the experiments. Ruthenium metal is thus the active element for the methane partial oxidation reaction.