Aspergillus niger ATCC 10864 was grown on bubble minicolumns aerated with pure oxygen either as biofilm or free-mycelium submerged systems. Growth kinetics was followed by estimating biomass from released carbon dioxide using a titration method and mathematical models. Submerged cultures showed increased endogenous respiration rates (0.0298 vs. 0.0004 g biomass/g biomass.h) possibly related to stress condition since this type of growth is not the natural way of life of A. niger. On the other hand, A. niger biofilm growth followed a logistic model having higher maximal specific growth rate than submerged cultures (0.061 vs. 0.045 h-1). This may be related to better mass transfer processes due to a channeled mycelial microstructure. Biofilm growth can be easily and reliable assessed by evaluating the CO2 released during the fermentation in minibioreactors. © 2011 Academic Journals.