We report on the experimental evaluation of a 5 kW solar chemical reactor for the steam-gasification of petcoke, carried out in a high-flux solar furnace. A petcoke-water slurry was continuously injected into a solar cavity-receiver to create a vortex flow directly exposed to concentrated solar radiation. For a nominal reactor temperature of 1500 K, a water-petcoke molar ratio of 4.8, and a residence time of 2.4 s, the maximum degree of petcoke conversion was 87%. Typical syngas composition produced was 62% H-2, 25% CO, 12% CO2, and 1% CH4. The solar energy conversion efficiency-defined as the portion of solar energy absorbed as chemical energy and sensible heat-attained 17%. The effect of varying the particle size (range 8.5-200 mu m) and slurry stoichiometry (range 2.1-6.3) on the degree of chemical conversion and energy conversion efficiency was examined. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.