The g.l.c. technique has been employed to measure formation constants of, and thermodynamic parameters for, complexes formed between benzene, toluene, and the xylenes and di-n-propyl tetrachlorophthalate in the temperature range 60–80°C. Infinite-dilution activity coefficients for the aromatic compounds in squalane are also obtained and interpreted. The method is shown to be competitive with existing techniques, and to offer a number of important advantages for studies in organic media.