In this article, the gas hydrate technique with propanone as the promoter was employed to separate methane + ethane gas mixtures. Experiments were performed in two different aqueous propanone concentrations, that is, 1.5 and 6 mol %. In addition, using a thermodynamic model, the compositions of gas mixtures in contact with hydrate phases were predicted. For this purpose, the solid solution theory of van der Waals and Platteeuw (vdWP), the state equation of Peng and Robinson, and three activity coefficient models (NRTL, UNIQUAC, and van Laar) were used to characterize the hydrate phase, the vapor phase, and the aqueous phase, respectively. The results were compared well with the experimental data and good agreement was found. Furthermore, the methane + ethane hydrate dissociation conditions in the presence of propanone were experimentally measured and predicted using the thermodynamic model. The model satisfactorily predicted the experimental values.