Ternary solid-liquid equilibrium diagrams of the systems methanol, thiourea and guests cyclohexane, methylcyclopentane (MCP), and their mixtures have been presented and discussed in the range between 30 and 60-degrees-C. A study of phase diagrams reveals that thiourea could successfully be used for the separation of cyclohexane and MCP from nonaromatic raffinate by adductive crystallization. Solubility limits for thiourea-cyclohexane adduct, thiourea-MCP adduct, and thiourea-MCP-cyclohexane adduct in ternary liquid solutions were measured over the entire feasible range of composition. Activity coefficients estimated for the saturation liquid solutions reflected strong positive deviation from ideality. Adduct solubilities increase with increase in the concentration of MCP guest and with increase in the temperature. In most cases adduct was found to be able to be formed near room temperature. The process of thiourea adduction, therefore, can be operated near room temperature.