Bubble column reactors are mechanical simple apparatuses, but the interactions between the liquid and gas phases have proven to be more complex. The description with an axial dispersion model has significantly disadvantages describing those physical phenomena. Although numerical fluid dynamics promising progress, not only backed by the increase in computational power and capacities, these calculations are not yet verifiable for industry sized reactors. An alternative approach is to divide the reactor in smaller material balance envelopes. This approach, known as compartment modeling, is explained and discussed in this article.