Solid oxide fuel cells (SOFCs) were characterized with methane as the fuel, both with and without an inert porous layer placed between the anode and the fuel stream. For a given set of operating conditions, SOFCs were stable without coking above a critical current density. The barrier layer decreased the critical current density, e.g. from 1.8 to < 0.6 A cm(-2) at 800 degrees C. This much-increased stable operating range is discussed in terms of mass transport through the barrier layer. (c) 2005 Elsevier B.V. All rights reserved.