Aqueous solutions of various surfactants, such as, sodium lauryl sulfate, lauryl alcohol-7-ethoxylate, cetyl pyridinium chloride, cetyl trimethylammonium bromide, etc. , at concentrations above their critical micelle concentration values, known as micellar solutions, and microemulsion solutions consisting of these surfactants and a co-surfactant, n-butanol, have been used successfully to separate mixtures of isomeric/non-isomeric close boiling substances like o-nitrochlorobenzene/p-nitrochlorobenzene, o-nitrotolunene/p-nitrotoluene, 2,6-xylenol/p-cresol, 2,4-dichlorophenol/2,4,6-trichlorophenol, o-isopropylphenol/p-isopropylphenol, from their solid mixtures. Exceptionally high values for the separation factor have been realized and these novel methods appear to be promising for industrial utilization.