A new measurement technique, photoluminescent volumetric imaging (PVI), has been developed for the visualization and quantification of multiphase flows and interface behavior in porous media. For this technique, a transparent, multiphase porous-medium system is constructed of optical-quality quartz sand, and two immiscible fluids matched to the optical refractive index of fused silica. Doping the fluids with property-selective fluorophores allows planar areas of the system to be successively excited with a shaped laser light to reveal the structure of the system. The resulting illumination is recorded by a high-resolution, cooled, slow scan charged-coupled device (CCD) camera. The planar digital images produced are then processed to generate a true three-dimensional data set that allows for quantitative study of the distribution of phases and interfaces within the porous medium. Sample volumes up to 125 mm3 in size with a resolution of better than 1 &mgr;m have been measured. Because of the large sample size and the high resolution of the measured data, geometric, flow, and phase interface information can be visualized and extracted at both subpore and system scales. ¿ American Geophysical Union 1995