Property tests were first conducted to characterize the subject oil-in water emulsions having three different interfacial tensions and three different droplet sizes in terms of their stability, droplet size distribution, and rheological behaviors. Then sandpack flow experiments were conducted, and permeability reduction tests were used to quantify the plugging performance of each of the different emulsions flowing at different flow rates through sandpacks. The results showed that the plugging effect of an oil-in-water emulsion was primarily due to the special flow behaviors of emulsion droplets in porous media; that is, the bulk viscosity of an emulsion contributed very little to the plugging effect. This paper has shown, for the first time, a correlation of emulsion plugging ability and interfacial tension. Permeability reduction of oil-in-water emulsions in sandpacks increased with an increase in interfacial tension and droplet size. At a fixed flow rate, emulsions with sigma = 5.2 mN/m and sigma = 9.3 mN/m had a more than 90% permeability reduction compared to the 66% reduction for the sigma = 0.15 mN/m emulsion, and the injection pressure drop for emulsion with the largest droplet size was more than three times greater than that with the smallest droplet size. That is because, when an emulsion droplet passed through the pore constriction, the capillary resistance force it experienced increased as the interfacial tension increased, and larger droplets were more likely to be trapped in the pore constrictions than smaller droplets, therefore causing greater restrictions to the flow. Flow experiments also showed that the permeability reduction of emulsions decreased with an increase of the flow rate. In addition, the size differences of emulsion droplets in the effluents and influents were also compared and analyzed.