Formation of biofilm within a porous matrix reduces the pore size and the total open space of the system, altering the porosity and permeability of the medium. This change in the pore size distribution can be quantified by expressing the porous structure with a proper geometrical model. A set of pertinent multispecies biofilm models is used to arrive at the dynamic biofilm thickness distribution. The obtained results are utilized within a modified Kozeny-Carman framework to establish permeability and porosity distribution during the biofilm formation. The biofilm thickness and the obtained permeability profile for a special microorganism, Pseudomonas aeruginosa, are compared with available experimental data. The potential reasons attributing to the differences between the numerical and experimental data are discussed. (C) 2008 Elsevier Ltd. All rights reserved.