AbstractThe gas hydrates of sulphur hexafluoride have been studied in the temperature interval from about −9°C. to 15°C. A quadruple point containing the four phases hydrate, water rich liquid, sulphur hexafluoride rich liquid, and vapor was found to exist at 14.0° C. and 293 lb./sq.in.abs. The pressure‐temperature data in the vicinity of 0°C. was used to show that the sulphur hexafluoride hydrate contains 17.02 moles of water per mole of sulphur hexafluoride. The difference in chemical potential between water in the hydrate lattice for Structure II and in ice calculated from this composition was found to be 211 cal/gm mole of water.Hydrates in the methane‐sulphur hexafluoride‐water system were studied at −3°C. over the full range of composition from 10.6 to 342 lb./sq.in.abs. Agreement between the experimental and predicted composition of the vapor and hydrate phases provides excellent confirmation of the applicability of the solution theory of hydrate formation to the methane‐sulphur hex