A table of McReynolds' constants is presented for a number of liquid phases selected on the basis of their popularity. This is the best scheme for arranging liquid phases according to chromatographic selectivity, but it is not perfect. The limitations of this scheme for predicting chromatographic selectivity are briefly reviewed: the effect of column temperature, phase loading, type of support, and column condition. A summary of practical experience is given which shows that the following list of gas chromatographic liquid phases should accomplish most gas chromatographic analyses: A poly(dimethylsiloxane), such as OV-101, SP-2100, OV-1, or SE-30 GC Grade. A poly(50%-methyl/50%-phenylsiloxane), such as OV-17 or SP-2250. A poly(alkyleneoxide), such as Carbowax 20M. A poly(cyanoalkylsiloxane) of medium cyanoalkyl content, such as AN-600, OV-225, SP-2300, or Silar 5CP. A poly(50%-methyl/50%-3,3,3-trifluoropropylsiloxane), such as OV-202 or SP-2401. The stability of gas chromatographic liquid phases when used is also reviewed. Both oxygen and water traps should be placed in the carrier gas delivery lines. Strong acids and bases, and strong Lewis acids and bases, should not be injected onto gas chromatographic liquid phases.