Abstract <p>The conditions of the formation of stable water–petroleum emulsions stabilized by clay particles were studied. The effect of unmodified and modified montmorillonite on the emulsion stabilization was studied for model systems consisting of pure toluene and distilled water. The clay particles were modified with resin–asphaltene components of the crude oil from the Romashkino oilfield. The influence exerted by the degree of modification and concentration of clay particles on the stability of water–petroleum emulsions was revealed. The degree of modification was estimated from the IR spectra. The resin–asphaltene components modify the surface of clay particles. The degree of modification increases with an increase in the modification time and concentration of petroleum components. Stable emulsion samples were obtained with modified clay particles. The toluene phase in these emulsions is stabilized by clay microparticles, which is characteristic of Pickering emulsions.</p>