Inverse gas chromatography has been widely used to determine the FloryHuggins parameter, ?, between two solvents. Many studies showed that interaction parameters were probe dependent. In recent studies, it was proposed that the interaction between two solvents may lead to different contact probability between solutes and solvent mixtures and create an apparent solubility parameter different from volume average rule. An equation was previously derived to relate the probe dependency to the deviation of solubility parameter from the volume average rule. By plotting ?2?3RT(?23/V2) versus the solubility parameter of solutes, a linear trend could be observed with a negative slope for miscible mixtures. When there was an unfavorable interaction between two solvents, an opposite situation would be observed. In this study, mixtures of 19,24-dioctadecyldotetracontane (C78) and its derivatives were tested. The solubility parameters of mixtures showed negative deviation from the volume average. The plots of ?2?3RT(?23/V2) versus solubility parameter of solutes had positive slopes. For two derivatives the best estimated values of RT(?23/V2) were negative in certain temperatures. Enthalpyentropy compensation plot showed that these two derivatives have higher entropy of mixing. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013