Hydrate structural transitions have recently been reported in the literature for the methane + ethane + water system. In this work, hydrate phase diagrams have been generated using regressed parameters for the van der Waals and Platteeuw statistical thermodynamic model. We will discuss the effect of temperature, pressure, and gas composition on the structural transition point. Predictions at and above incipient hydrate formation conditions reveal unusual phenomena such as minimum pressure azeotropes and solid-solid phase equilibria.