Inverse gas chromatography (i.g.c.) has been used to calculate thermodynamic interaction parameters of polystyrene (PS) and polybutadiene (PBD) with 15 different probes of varying polarities at 155, 165, 175 and 185-degrees-C. Polymer-polymer interaction parameters were also evaluated at five different compositions of PS-PBD blends and were found to show marked probe dependence. Using various approaches such as those given by Horta et al., by Sanchez and by Chee, the experimental data have been analysed to provide probe-independent interaction parameters. It is shown that rearrangement of an equation due to Su and Patterson explains the DELTAchi effect and gives probe-independent interaction parameters by a more simplified method.