Abstract: The vacuum volumetric method was used to determine the gas contents of both the man-made methane hydrates in various sediments and the natural gas hydrates recovered from the Shenhu area in the South China Sea and the Qilian Mountain permafrost.Apparent hydration numbers (water/gas molar ratio) of the samples were calculated,and the methods for measuring gas content from the gas hydrate samples discussed.The experimental results show that the synthetic methane hydrates have small apparent hydration numbers which are close to the crystal hydration number.The pure hydrate concentration of the samples as well as the gas contents is high.However,the apparent hydration numbers of the samples from the Shenhu area and Qilian Mountain permafrost are generally low,but much higher than their crystal hydration number.In these samples,both the pure hydrate concentration and gas contents are low due to the high amount of pore water in the samples.