Direct utilization of hydrocarbons in low temperature solid oxide fuel cells is of growing interest in the landscape of alternative energy technologies. Here, we report on performance of self-supported microsolid oxide fuel cells (mu SOFCs) with ruthenium (Ru) nano-porous thin film anodes operating in natural gas and methane. The mu SOFCs consist of 8 mol% yttria-stabilized zirconia thin film electrolytes, porous platinum cathodes and porous Ru anodes, and were tested with dry natural gas and methane as fuels and air as the oxidant. At 500 degrees C, comparable power densities of 410 mW cm(-2) and 440 mW cm(-2) were obtained with dry natural gas and methane, respectively. In weakly humidified natural gas, open circuit voltage of 0.95 V at 530 degrees C with peak power density of 800 mW cm(-2) was realized. The mu SOFC was continuously operated at constant voltage of 0.7 V with methane, where quasi-periodic oscillatory behavior of the performance was observed. Through post-operation XPS studies it was found that the oxidation state of Ru anode surfaces significantly differs depending on the fuel used, oxidation being enhanced with methane or natural gas. The nature of the oscillation is discussed based on the transition in surface oxygen coverage states and electro-catalytic activity of Ru anodes. (c) 2013 Elsevier B.V. All rights reserved.