The effects of pressure and surfactants on the phase holdups and flow regime transition velocities of gas-liquid-solid fluidized beds were investigated. The effect of pressure on the bed phase holdups is significant and more pronounced at larger gas flow rates where pressure has a greater effect on the equilibrium bubble size. The addition of a surfactant leads to an increase in the gas holdup and a lowering of the solids and liquid holdups. The presence of a surfactant with a liquid flow results in shearing of the bubbles across the gas-liquid distributor, limiting the effect of pressure. Finally, for all conditions, gas holdups in the freeboard region were greater than in the bed.