A population balance model formulation for predicting the size distribution of the dispersed gas phase in bubble column reactors is presented. Extended source term parametrizations for the breakup and coalescence mechanisms are included in a computational fluid dynamics (CFD) model and tested on a fairly simple flow formulation corresponding to locally obtained experimental data. Most CFD codes are based on the assumption of a monodisperse bubble size distribution resulting in an inaccurate prediction of the hold-up. Comparing the results obtained by the breakup model versions against experimental data indicates that the extended model provides an improved description of the bubble size distribution, hold-up, and thus also the volume-averaged gas-phase velocity.