The changes of standard thermodynamic functions (Delta H degrees and Delta S degrees) for 21 organic compounds dissolved in supported polyethylene glycol-6000 from gas phase have been determined using gas-liquid chromatographic technique. The experimental thermodynamic data have been discussed in the light of interaction between molecules of the solvent and solute. Selective intermolecular forces are believed to be the main cause of PEG selectively dissolving and separating solutes. Selectivity of the PEG is not only observed to polar substances but also to apolar ones such as benzene and cyclohexane. We believe that the macromolecule can adjust its conformation when it receives a solute molecule, so as to more strongly interact with the small molecule. When such strong negative electric groups as carbonyl oxygen atom, nitro group approach ethylene of PEG or strongly positive charged hydrogen atom(s) approach(s) an oxygen atom of PEG, strong intermolecular forces occur and solution heats are large. On the other hand, strongly intermolecular force may be caused by a kind of synergistic interaction between the solvent and solute molecules. In such a case, a solute molecule is attracted by two or more sites on the polymer chain.