Bubble size distribution and the gas-liquid specific interfacial area were measured as a function of axial location, nozzle diameter and superficial liquid and gas velocities in a modified bubble column reactor. The experimental measurements of bubble size and its distribution are analyzed with distribution model to gain insight into the breakup and coalescence mechanisms taking place. Axial profile of bubble number flux was estimated based on size distribution model incorporated with coalescence phenomena. Also correlation for Sauter mean bubble diameter has been developed with operating variables. (c) 2006 Elsevier B.V. All rights reserved.