We experimentally and theoretically investigate the formation of bubbles on wetted and non-wetted sieves and porous plates, which are submerged in an inviscid liquid. It, is assumed that the process of bubble formation occurs as if each bubble were alone on the plate. The interaction between orifices is modeled by estimating the gas flow field caused by a growing bubble. Depending on the material below the plate, a growing bubble influences the formation of bubbles at other orifices either in its vicinity or over the whole plate, and bubbling sites are regularly or irregularly distributed over the plate. Values for the volume fluxes at which the bubbling behavior changes are given, e.g., the minimum gas volume flux at which a disperser becomes effective or the volume flux at which growing bubbles densely populate the plates. For an example system of air in water we discuss the four cases of wetted sieve, non-wetted sieve, wetted porous plate and non-wetted porous plate. We present data for a non-wetted porous plate and find fair agreement between theoretical predictions and experiment. (C) 2003 Elsevier Ltd. All rights reserved.