A previous scheme for the classification of various solvents according to their polarity P' and selectivity (xe,xd,xn) has been modified, leading to greater precision in these calculated solvent parameters. This scheme has been further extended for the case of liquids used as gas chromatography (GC) stationary phases, allowing classification of additional solvents studied by McReynolds. The greater precision of these resulting data allows a number of further checks on the utility of this approach to solvent classification, and allows most common solvents to be characterized according to different selectivity groups. The present study also confirms that three polar test-solutes suffice to establish the primary selectivity characteristics of various solvents. Dispersion interactions In solutions of polar solvents appear to play an unimportant role in contributing to solvent selectivity.