A thermodynamic model for the prediction of pressure-temperature phase diagrams of structures II and H clathrate hydrates of methane, carbon dioxide, or hydrogen sulfide in the presence of "water-insoluble'' organic componds is presented. The model is based on the equality of water fugacity in the aqueous and hydrate phases. The solid solution theory of van der Waals-Platteeuw (vdW-P) is used for calculation of the fugacity of water in the hydrate phase. The Peng-Robinson (PR) equation of state (EoS) is employed to calculate the fugacity of the components in the gas phase. It is assumed that the gas phase is water and promoter free and the organic compounds do not have marked effects on water activity in the aqueous phase. The results of this model are compared to existing experimental data from the literature. Acceptable agreement is found between the model predictions and the investigated experimental data.