One important challenge in chemical industry, especially for processes of synthesis fuels, is the development of effective three-phase reactors for high pressure and temperature. In the present study, a novel airlift internal-loop reactor (ALR) was proposed and its hydrodynamic behaviors were experimentally studied. The local bubble rise velocity and liquid velocity are measured under different operating conditions. The influence of operating conditions including the superficial gas velocity and solid holdup on the bubble rise velocity and liquid velocity in the riser was studied. A mathematical model was proposed based on the energy balance to describe the multiphase flow characteristics in the internal-loop airlift reactor. The comparison between the calculated and experimental values shows that the proposed model can predict the flow behavior reasonably. (c) 2005 Elsevier B.V. All rights reserved.