Bubble column and three-phase fluidized bed reactors have wide applications in biotechnological and petroleum processes (Deckwer, 1985;Fan, 1989). In such biotechnological processes as fermentation and waste water treatment, small bubbles of oxygen and/or nitrogen are introduced in the column to enhance oxygen transfer and to ensure the stability of immobilized cell particles. In addition, tiny bubbles are formed by such gases as C02, H2, and CHI, which are produced during the biological process due to the production of surface active compounds. The presence of these small bubbles causes an increase in the gas holdup of the system. High gas holdups are also characteristics of industrial processes such as coal liquefaction and hydrotreating of residual oils. Tarmy et al. (1984) studied high gas holdup behavior in pilot-and large-scale coal liquefaction reactors and reported gas holdup as high as 50 ~0 1 % .Such high gas holdups were attributed to the formation of small rigid bubbles with noncoalescing tendencies due to high-pressure and high-temperature operations. Blum and Toman (1977) reported a maximum gas holdup of 0.5 in a hightemperature (100 to 350"C, 6.9 MPa) three-phase fluidized bed methanator. Thus, good understanding of the transport properties of three-phase fluidized beds with high gas holdups is essential to the design, control and optimum operations of the commercial reactors employed in the above-mentioned processes.High gas holdups in laboratory scale under ambient conditions can be obtained by the addition of surfactants in airwater and air-water-solid systems. Such high gas holdups in the presence of a surfactant simulate the conditions commonly encountered in coal liquefaction and petroleum resids hydrotreating operations. Levich (1962) reported that the presence of surfactants induces a noncoalescing tendency in the gasliquid flow and reduces the bubble rise velocity significantly by creating surface tension gradients that cause tangential stresses along the bubble surface. The addition of surfactants to pure water systems, however, increases the system complexity by altering the average bubble size, gas holdup, and bubble-particle interactions. This causes the flow regime transition which affects the heat-transfer behavior of the system. In addition to the dependence on liquid properties, operating