Isothermal three-phase equilibria of gas, aqueous, and hydrate phases for the {xenon (Xe) + cyclopropane (c-C3H6)} mixed-gas hydrate system were measured at two different temperatures (279.15 and 289.15) K. The structural phase transitions from structure-I to structure-II and back to structure-I, depending on the mole fraction of guest mixtures, occur in the (Xe + c-C3H6) mixed-gas hydrate system. The isothermal pressure-composition relations have two local pressure minima. The most important characteristic in the (Xe + c-C3H6) mixed-gas hydrate system is that the equilibrium pressure-composition relations exhibit the complex phase behavior involving two structural phase transitions and two homogeneous negative azeotropes. One of two structural phase transitions exhibits the heterogeneous azeotropic-like behavior. (C) 2011 Elsevier Ltd. All rights reserved.