A novel variable-volume type high-pressure apparatus has been designed, constructed and used for gas hydrate investigations. The apparatus has an operating temperature ranging from 253 K to 473 K and pressure ranging from 0.1 MPa to 60 MPa. Its central component consists of a viewing windows cell to which several sensors or analytical instruments can be connected. At its present configuration, a Raman spectrometer and a gas chromatograph are connected for the study of the liquid (or solid) and the gas phases respectively. The apparatus was used for the study of two different systems. The first system was composed of carbon dioxide (CO2) and water for which the hydrate formation and dissolution has been investigated by injecting water into liquid CO2. The evolution of the system was monitored by means of visual observation in combination with Raman spectroscopy. The second system consists of thermogenic-like gases (i.e. synthetic natural gas) for which the hydrate formation and dissociation have additionally been investigated by monitoring the change of the vapour phase composition. The consequences of the destruction of the hydrate skin formed at the water gas interface have been studied. Thus, an attempt has been made to study the importance of the interfacial contact layer between the gas phase and the aqueous phase for the hydrate growth process. In this paper, we describe in detail the apparatus, followed by the presentation of the results on both systems investigated. (C) 2010 Elsevier Ltd. All rights reserved.