Hydrate numbers, n, were directly determined by two methods using a new apparatus, designed to alleviate the occlusion of liquid water in the hydrate crystal and to operate up to 15,000 psi in order to evaluate the pressure dependence of the hydrate composition. Experimental conditions for ethane were 1 18.0 psia at 40.0°F, 119.4 psia at 40.2"F, and 225 psia at 48.9"F. The experimental ethane hydrate numbers were from 7.90 to 8.46 with an average maximum relative uncertainty of &4.24/,. Four sets of experimental conditions were used for methane hydrate: 1030 psia at 5O.O0F, 1032 psia at 50.1 OF, 1901 psia at 59.9"F, and 1902 psia at 60.0"F. The experimental hydrate numbers were from 5.84 to 6.34 with an average maximum relative uncertainty of =t 1 5.6y0. Predictions for n from the solid solution theory of van der Waals and Platteeuw are discussed.