Two approaches are adopted in this study to identify the flow transition in a bubble column from the homogeneous regime to the heterogeneous regime at pressures up to 15.2 MPa and temperatures up to 78 degrees C. These approaches, which yield essentially identical results, include those based on the standard deviation of the pressure fluctuation and the drift flux model. The experimental results obtained indicate that the regime transition velocity is delayed when the system pressure and temperature increase. The correlation proposed for the transition velocity by Wilkinson et al. (1992) predicts the present results to a reasonable extent, provided that the experimentally measured values for the physical properties of the fluids are used in the correlation. It is clear, however, that an improved correlation or model is needed for a quantitative account of the transition velocity for high-pressure bubble column systems with different gas distributing capability.