In this study the flow characteristics in the pipe-flow zone of a plunging liquid jet bubble column are investigated. The effect of column diameter, and gas and liquid flow rates on the bubble size and gas void fraction for the bubbly and churn-turbulent flow regimes are determined experimentally for an air-water system. Applying drift-flux analysis to the flow, it was found that in the bubbly flow regime the distribution coefficient was approximately equal to 2 at a liquid Reynolds number of 1500, decreasing to approximately unity for a liquid Reynolds number above 10 000. A similar trend was observed for the churn-turbulent flow regime, with distribution coefficient values in the range 1.10 to 0.91 over a similar range of liquid Reynolds numbers. It was also found that the bubble size remained constant in the bubbly flow regime. In the churn-turbulent flow regime, however, an increase in bubble size was observed due to coalescence.