Phase inversion phenomena of oil-in-water (triolein in water-containing sodium lauryl sulfate, SDS) emulsions permeating through hydrophobic micropores were visualized using an optically accessible array of well-defined microchannels and a microscope video system. Oil droplets coalesced on the hydrophobic microchannel surface and permeated to form a continuous oil layer at the outlet Water was repelled fi om the surface, and large, irregular-sized water droplets were created at the outlet To evaluate the emulsion breakdown mechanism practically, the emulsions were filtered with hydrophobic polytetrafluoroethylene membranes of several pole sizes. In all cases, the permeate was separated into two phases, an oily and an aqueous one. The three pore sizes, 1-, 5- and 10-mu m membranes, were stacked into a layer, and with the multilayer membrane the breakdown ability of the 1-mu m membrane was effectively combined with the oil droplet growth ability of the 5- and 10-mu m membranes.