The formation of hydrates in pipe lines transmission has caused many problems in the oil and gas industry. It is crucial to prevent hydrate formation and postpone it, and much research has been done to eliminate this phenomenon by the oil and gas industry. There are several methods to prevent and eliminate hydrate formation, one of which is the use of thermodynamic inhibitors. Substances such as methanol, ethanol, monoethylene glycol (MEG) are known as the most widely known inhibitors. Recently, some materials, such as ionic liquids, play the role of thermodynamic inhibitors. One of the issues that should be considered is prediction of the conditions for the formation of hydrate sediments in the presence and absence of inhibitors that requiring a precise thermodynamic modeling. In this study, the equilibrium temperature and pressure of hydrate formation for pure gases and gas mixtures in the presence of thermodynamic inhibitors such as methanol, ethanol, monoethylene glycol and ionic liquids have been calculated. Ionic liquids studied in this study include: [EMIM][HSO 4 ], [EMIM][EtSO 4 ], [BMIM][BF 4 ], [BMIM][Cl], [BMIM][Br] and [OH-EMIM][BF 4 ]. For modeling, the two-step hydrate formation theory of Chen-Guo and the Cubic Plus Association (CPA) equation of state has been used to calculate fugacity in liquid and vapor phases. Hydrate calculations of methane and carbon dioxide were carried out in the presence of industrial inhibitors and it was shown that the model used for hydrate calculations has an acceptable accuracy to predict the formation of hydrate in the presence of these inhibitors. For example, the absolute average deviation of methane gas hydrates in the presence of monoethylene glycol by using the CPA equation of state and the theory of Chen-Guo is 3.29%, while the absolute average deviation of this system, by using the SRK equation of state and the theory of Chen-Guo is 10.87%. Therefore, the model used in this study can well predict thermodynamically the systems that make up the hydrogen bond (for example, hydrate formation in the presence of methanol and monoethylene glycol). Ionic liquids have recently been used as kinetic and thermodynamic inhibitors. To model ionic liquids by using the CPA equation of state, we must first obtain the required parameters for ionic liquids. For this purpose, the parameters of the equation of state for ionic liquids are calculated by using pure liquid density. Also, the interaction parameters of ionic liquids-water and ionic liquids-methane were determined by using equilibrium data. Then, modeling the conditions for the formation of methane hydrates in the presence of ionic liquids was carried out by using the CPA equation of state and the two-step hydrate formation theory and the results were compared with the experimental data as well as the conditions for using the SRK equation of state. The results show that the CPA equation of state can well predict the phase behavior of ionic liquids based imidazolium with regard to the 2B scheme. Also, the results show that the model used in this study is accurate to predict the methane hydrate formation in the presence of ionic liquids based imidazolium. For example, the average absolute deviation of methane hydrates in the presence of 1-butyl-3-methyl-imidazolium tetrafluoroborate in various concentrations is less than 4.2%.