With the objective of estimating the solubility of a pure hydrocarbon hydrate former in pure water in equilibrium with gas hydrates, a simple thermodynamic model has been developed, based on the equality of water fugacity in the liquid water and hydrate phases. The solid solution theory of van der Waals-Platteeuw has been applied to calculate the fugacity of water in the hydrate phase. The Henry's law approach and the activity coefficient method have been used to calculate the fugacities of the hydrocarbon hydrate former and water in the liquid water phase, respectively. The results of this model are compared with some selected experimental data from the literature. Acceptable agreements between the model predictions and experimental data demonstrate the reliability of the model developed in this work, Finally, the possible errors sources in model predictions are discussed.