Equilibrium conditions for hydrate formation from binary mixtures of C2H6, C3H8 and noble gases such as Ar, Kr and Xe were experimentally determined at the temperatures of 273.5, 276.5 and 278.5 K. The binary systems of Xe + C3H8, Kr + C3H8 and Kr + C2H6 mixtures have hydrate azeotropes with pressure minimum points in the isothermal pressure-composition diagrams. Hydrate structural transitions were also observed in the binary systems of Xe + C3H8 and Kr + C2H6 mixtures. (c) 2006 Elsevier B.V. All rights reserved.