The expansion of possible areas of use of modern gas chromatography is largely determined by the thermal stability of stationary liquid phases (SLP), which allows the separation of complex mixtures of high-boiling compounds. A way to increase the thermal stability of nonpolar and weakly polar polysiloxane SLPs is to introduce rigid fragments into the polysiloxane chain. Currently, there is an extensive set of columns with thermostable SLPs, which, in some cases, have the index “ms”. However, in most cases, the nature of these phases and the methods for preparing the columns are not disclosed. In this work, using the linear free energy relationship (LFER) model, we compared the selectivity of a number of proprietary columns with in-house columns in which the siloxane–silarylene phase and the column preparation methods themselves are known. Various types of intermolecular interactions are considered within the framework of the LFER model.