It has been suggested that oil migrates through reservoir sands in the form of a fine, disperse emulsion of oil in water, and that oil accumulations occur where the stream enters finer-grained rock such as silt or shale. In order to investigate the possible mechanisms, stable emulsions of oil in water were prepared without the use of wetting agents. They consisted of droplets 1/2 to 1-1/2 microns in diameter, in a concentration of 20 to 40 parts of oil per million of water. These emulsions passed freely through filter paper and ordinary passed freely through filter paper and ordinary sand. A plastic tube containing glass beads of 200-microns diameter included a bed 1/2-cm thick of crushed beads 37 to 88 microns in diameter. When the emulsion was passed through this tube, up to 80 percent of the oil was screened out at the coarse-fine interface. The amount removed depended on the contrast in grain size, the nature and the preferential wettability of the media. Similar results occurred when quartz sand was used as the coarse, and crushed sand as the fine medium. This screening did not occur as a result of capillary effects., because the pores were many times the diameter of the droplets. The oil collected as a result of flocculation of the droplets into strings and clusters., and the oil saturation in the pores consisted of masses of droplets with very little coalescence. Possibly electrostatic forces are more important Possibly electrostatic forces are more important than capillary in the behavior of fine, disperse, oil-in-water emulsions. our current ideas on multiphase flow in porous media may not apply to disperse emulsions.