Steam reforming of methane was studied over gadolinia-doped ceria (CDC) supported Ni catalysts. Ni content varied from 1 to 10wt% and molar ratio of H2O to CH4 was 2 in feed. A Ni content of about 5wt% leads to highest formation rates of both hydrogen and CO2. Over 1 wt% Ni/GDC catalyst at 700 degrees C, the hydrogen yield equals almost 4 for complete CO2 formation. Increasing Ni content leads to decreasing hydrogen yield. A Ni content of about 5 wt% or lower is beneficial for high CO2 selectivity and low carbon deposition associated with high methane conversion. Increased Ni content results in larger Ni particle size and increased carbon deposition. (C) 2008 Elsevier B.V. All rights reserved.