An experimental approach to study physical processes affecting fluid behavior in three-fluid porous media systems was designed and implemented. These experiments were designed to provide quantitative evidence of important pore-scale displacement processes. A unique experimental approach using a two-dimensional synthetic porous medium (micromodel) and digital image analysis (DIA) enabled both measurement of three-fluid capillary pressure--saturation relationships and analysis of fluid behavior at the pore level. Experiments were pressure controlled, and were designed to mimic measurements typically performed on laboratory cores. Only quasi-static measurements were made, with a focus on capillary pressure--saturation relations. Different orders of fluid infiltration with respect to wettability were studied. DIA made it possible to obtain quantitative information about the experiments, including fluid saturations, saturation changes between pressure steps, and movement of apparently isolated fluids through films. The results provide insights into important pore-scale mechanisms and provide a basis for three-fluid pore-scale computations. ¿ American Geophysical Union 1993