Cyclopentane and neopentane have only recently been recognised as a potential hydrate former, forming structure-II gas hydrates. However, no information on their hydrate phase boundary or modelling has yet been reported. In this paper, experimental hydrate dissociation data for cyclopentane and neopentane in their binaries and ternaries with methane or/and nitrogen (i.e., methane/cyclopentane, nitrogen/cyclopentane, methane/nitrogen/cyclopentane, methane/neopentane, nitrogen/neopentane, and methane/nitrogen/neopentane) over a wide range of temperature (282-301 K and 276-293 K, respectively) have been reported. The results of comparison with other newly discovered hydrate forming compounds showed that cyclopentane is the strongest hydrate promoter with neopentane in the second place. The predicted hydrate free zone is in good agreement with the experimental data, demonstrating the success of modelling. © 1997 Elsevier Science B.V.