The phase behavior of hydrocarbon mixtures where one of the constituents self-aggregates is a subject of significant industrial and academic interest. Here, a nonintrusive acoustic phased-array technique operated in pulse echo mode is used to investigate the phase behavior of asphaltenes, a well-known self-aggregating species, in mixtures with polystyrene and toluene at 293 K and atmospheric pressure. This mixture exhibits liquid-liquid phase behavior where both liquids are opaque to visible light, are of uniform composition, and are stable over broad ranges of composition. One. phase is asphaltene rich and the other phase is polystyrene rich. Varying the polystyrene mean molar mass had little impact on the liquid to liquid-liquid phase boundaries. Liquid-liquid critical points were identified and phase compositions were confirmed for a fixed global composition using the UV-visible spectrophotometry and mass balance equations. This is the first report of liquid-liquid phase behavior for such mixtures. Depletion flocculation is hypothesized to be the mechanism causing phase separation in this ternary mixture.