Gas-liquid reactors involving the production of bubbles are very useful in various industrial fields, such as chemistry, oil refining, or water treatment. Generating microbubbles at the inlet of gas-liquid reactors could improve both hydrodynamics and mass transfer. In this paper, the generation of microbubbles using commercial porous filtration membranes is studied, in aqueous or organic liquid under a liquid cross-flow. Different combinations of dispersed phase (air or nitrogen) and continuous phase (water or heptane) are studied. Since the size of the microbubbles may be correlated with physicochemical properties of both phases and the membrane surface, several tubular ceramic membranes were tested (made of alumina or zirconium oxides) with mean pore diameters d(p) varying from 20 to 800 nm. It was observed that these membranes were able to generate bubbles which became microbubbles under the application of a liquid cross-flow. Microbubbles with bimodal distribution (microbubble diameters d(b) in the range of 100-200 and 500-550 mu m) were obtained in heptane when using zirconium oxide membranes (d(p) varying from 20 to 100 nm) under a shear stress tau varying from 27 to 39 Pa with a gas fraction of nearly 3%. The present study shows that microbubbles can be generated in heptane using commercial porous filtration membranes under a liquid cross-flow. This is a promising way to provide microbubbles that could be used to improve the usual gas/liquid mass transfer operation.