During the development of the downflow bubble column, knowledge of the specific interfacial area was a precondition for assessing the mass transfer performance. A comparison with other gas/liquid contactors shows that, in the downflow bubble column, higher mass transfer areas can be obtained than, for example, in a bottom-sparged bubble column or in a loop-type reactor in the region of high liquid throughputs. Examples for practical performance of downflow bubble columns are given, based on the derived correlations.