With growing interest in gas hydrates as a possible energy resource, there have been necessities for more experimental data and prediction methods for properties of hydrate-containing systems. An experimental apparatus was developed for the determination of the equilibrium pressure of hydrates and solubilities of sparingly soluble gases in hydrate-liquid water equilibria. Methane and ethane solubilities in hydrate-liquid water equilibria were measured in the pressure range from 5 to 20 MPa and in temperature range of 276-282 K. A unified prediction method for the hydrate-containing phase equilibria for single- and mixed-guest species was developed. Hydrate-containing systems of methane, ethane, and propane were modeled using a unified approach. A lattice-fluid equation of state was used consistently for the fluid phases. Various hydrate-containing equilibria of simple and mixed hydrate were predicted and compared with literature data and the present experimental results.