Phase equilibria of water–alcohol–hydrocarbons are important when it comes to flow assurance issues in the petroleum industry. Thermodynamic inhibitors [usually alcohols and glycols, such as methanol and monoethylene glycol (MEG)] change the thermodynamic equilibrium, thus avoiding the hydrate zone. Accurate results for the loss of the volatile inhibitor in the gas or condensate phase (partition) are of extreme importance for the oil and gas industry. In this work, a flash algorithm using the cubic-plus-association (CPA) equation of state was developed to estimate the partition of each component (water, hydrate-forming gas, and inhibitor) in any phase over a wide range of temperatures and pressures in vapor–liquid equilibrium and liquid–liquid equilibrium. Different temperature-dependent functions were optimized and evaluated for the CPA binary interaction parameters. The flash algorithm was applied to several systems with water, methane, ethane, propane, carbon dioxide, methanol, and monoethylene glycol (MEG). The results were then compared with experimental data available in the literature. The loss of methanol to the gas and/or condensate phases was satisfactorily predicted. Yet, the CPA underestimated the loss of MEG to the gas phase in a gas mixture containing carbon dioxide. The average absolute deviation for the predicted loss of methanol and monoethylene glycol ranged between 3 and 45%.