Due to their high operating temperatures, SOFCs can be directly fed with biogas, mainly composed of CH4 and CO2. In this work, experiments was performed with a classical Ni-YSZcermet//YSZ//LSM cell fed either with a synthetic simulated biogas (CH4/CO2 ratio equal to 1 with 6% humidity), or with humidified H-2. In both cases, the performances are found to be very similar, which confirms the ability of SOFCs to operate with internal reforming of biogas. Nevertheless, carbon formation in these operating conditions needs to be considered because of durability concerns. Thermodynamic calculations and modelling are carried out to evaluate the risk of carbon deposition depending on operating parameters. In the ternary diagram C-H-O, the limits for carbon deposition are plotted, allowing the determination of "safe" operating conditions in terms of CH4 inlet flow rate and cell voltage. First experiments confirm these modelling results. (C) 2011 Published by Elsevier B.V.