Abstract: Cyanoethyl derivatives and sulfoxides have good solvent properties for aromatics. Ternary systems of different groupings have been investigated. These include thio-dipropionitrile and oxy-dipropionitrile; alkanes, cyclanes, olefines, cycloolefines; and monocyclic and bicyclic aromatics. Ternary system with dimethyl sulfoxide was also studied. In liquid-liquid extraction, compromise has always to be made between selectivity and solubility. A method for the choice of solvents was presented. The results indicate that the order of adaptability is dimethyl sulfoxide> oxy-dipropionitrile> thio-propionitrile.