Gas holdup and liquid circulation of one conventional draft tube and three different convergence-divergence draft tubes in an internal loop airlift reactor were investigated. Experiments were carried out in two-phase systems with air;water and air-CMC (carboxyl methylcellulose) solution and three-phase system with air-water-resin particles. The two-phase drift-flux model was used to estimate gas holdup for three-phase Newtonian and two-phase non-Newtonian systems. It is shown that gas holdup in convergence-divergence draft tubes is higher than that in a conventional draft tube and increases with superficial gas velocity. Variation of the structural parameters of convergence-divergence draft tubes has little effect on gas holdup in the two-phase and three-phase system. The mathematical model, which is based on a drift-flux model, was developed to describe the liquid circulation velocity in the reactor satisfactorily.