Occluded gases were studied from fifteen types of rock, including igneous, metamorphic and sedimentary. The specimens were stressed to a crushing failure at room temperature under a vacuum of about 10-9 torr. The more abundant gases were H2, CH4, H2O, N2, CO, O2 and CO2. However, each rock released gas with a characteristic composition. The volume of gas released was a variable function of stress above a threshold value. The greatest rate of emission occurred over the latter 20% of the rock's ability to withstand stress. Analyses of stress-released occluded gases (excluding water), released as a function of stress, are given for a granodiorite and a gneiss. Volumes (STP) of most gases observed prior to an upon failure of the rocks are equivalent to several hundred liters each per ton of rock. Stress-induced emission of a widely distributed, highly mobile gas such as H2 could serve as an useful indicator of a critical stress build-up in the earth's crust.