The effects of the gas velocity (0.05-0.22 m/s) and temperature (870-970 degrees C) on the gas holdup and the gas phase axial dispersion coefficient have been studied in a molten salt oxidation reactor (0.076 m i.d. x 0.653 m H., air-molten sodium carbonate salt two-phase system). The gas phase holdup and the amount of the axial gas phase dispersion coefficient were experimentally evaluated by means of the pressure drop measurement and residence time distribution (RTD) experiments using inert tracer gas (CO), respectively. Results indicated that the gas holdup increases with an increasing temperature, but the increasing rate of the gas holdup decreases with an increasing gas velocity. The gas phase axial dispersion coefficients show an asymptotic value with an increasing gas velocity due to the plug-flow like behavior at a higher gas velocity. Temperature has positive effects on the gas phase axial dispersion. To detect the regime characteristics, a spectral method based on the differential pressure fluctuation has been applied, which enables us to obtain the flow characteristics in the MSO reactor. (c) 2005 Elsevier B.V. All rights reserved.