The effect of elevated pressures on the gas holdup and flow regime transition in a gas-liquid bubble column is examined. Experiments are carried out in a bubble column of 0.3 m diameter at system pressures between 0.1 and 0.6MPa, using different liquids sparged with nitrogen. The following results are obtained. (1) The superficial gas velocity at the flow regime transition point (U-trans) increases with the system pressure. (2) In the bubbly flow regime, the gas holdup shows no notable change when the superficial gas velocity is maintained at a low value. However, in the churn-turbulent flow regime, the gas holdup increases with the system pressure. These phenomena are in agreement with those predicted on the basis of the equations for Utrans and gas holdup, proposed previously.