Experimental heat capacity data of simple gas hydrates on xenon, methane, ethane, and propane are reduced by application of classical thermodynamics and the ideal solid solution theory. It is shown that calculated heat capacities of the empty hydrate lattices of the structure I and II hydrates can be higher or lower than the heat capacity of ice. Similarly, the calculated partial molar heat capacity of the enclathrated gases are higher or lower than the corresponding experimental ideal gas heat capacity. These differences depend on the size of the guest relative to the cavity, the hydrate number, and the temperature. For estimation of the thermodynamic properties of the empty hydrate lattice, further experimental work is recommended. Within the present limitations, a consistent methodology is applied for the prediction of the heat capacity of a natural gas hydrate.