We present a model explaining the mechanism of water-in-oil (W/O) emulsion Stabilization in petroleum systems. According to the model, W/O petroleum emulsions are stabilized by at least two types of chemicals: one is a small subfraction of asphaltenes, and the other is a low-molecular-weight, surfactant-like material. Their competition for the oil/water interface is based on adsorption kinetics, rather than on differences in adsorption energies. The asphaltenic material adsorbs slowly and irreversibly and forms rigid skins, Surfactant-like species adsorb fast, reaching equilibrium. Both are effective emulsifiers; however, emulsion breaking requires different strategies, depending on the stabilizer.