The underlying mechanism and the generality of the drag correction factor C-D/C-DO, which was developed and applied in the simulation of bubble columns at elevated pressure in our recent work, was discussed in detail. With this drag model, numerical simulations of a bubble column were carried out by computational fluid dynamics (CFD) coupled with the population balance model (PBM). The complex variations of the drag correction factor and slip velocity with increasing local gas holdup were well predicted. The results confirmed that the drag correction should be based on the bubble size distribution and local gas holdup, instead of on the superficial gas velocity or overall gas holdup as commonly reported in the literature. The good predictions of the gas holdup and gas-liquid mass transfer in both water and high-viscosity liquids showed that the CFD-PBM model was powerful for the simulation of bubble columns under complex operating conditions. (C) 2018 Published by Elsevier Ltd.