From the perspective of energy security and environmental sustainability, the use of currently underutilized residual heavy oil can increase the value and applicability of Integrated Gasification Combined Cycle (IGCC) power generation systems. In order to utilize such fuel in IGCC applications reliably and effectively, it is essential to understand the phenomena within the gasifier. Therefore, the gasification characteristics of Orimulsion (TM) (registered trademark of BITOR Ltd) were studied using a 2.4 t/d research. The gasifier has many unique measurement devices, such as heat flux probes, sampling devices for hot gas and partially reacted solids, an optical gas analyzer (laser Raman), etc. The gasifier provides a range of performance indicators, such as calorific value of the product gas, cold gas efficiency, carbon conversion efficiency, and the vertical distribution of those results. Gasification reaction mechanisms and the vertical distribution of heat flux, which are required for effective modeling of gasification phenomena, were also studied under various operating conditions. These results are of the form that can be used in the design and operation of actual gasifiers for use with feedstocks like Orimulsion (TM). (c) 2004 Elsevier Ltd. All rights reserved.