AbstractGas‐liquid critical temperatures have been measured for binary mixtures of the polar compounds acetonitrile, 2‐butanone and monochlorobenzene + 2,2,4‐trimethylpentane or + n‐alkanes as well as + some other polar compounds. The data were analysed in terms of a parameter of interaction between unlike molecules using conformal solution theory. It was shown that the shape of the molecules did not play an important role at the critical state. The strength of intermolecular interaction could be quantified and corresponded to the excess properties of the same mixtures in the liquid state.