Experiments and calculations were performed to determine the amount of gas released from heated oil shale. It is known that kerogen, a component of oil shale, releases gas when heated. When the temperature is increased, the kerogen yields not only gas but char, a solid that reacts with steam and CO/sub 2/ (by-products of heated shale) to yield H/sub 2/ and CO. It was found that as much as 200 moles of CO and H/sub 2/ could be produced by the reaction of 1 kg of kerogen with steam at 1200/sup 0/C. Another of the gas-releasing components of oil shale, carbonate minerals, begins to decompose at 500/sup 0/C; decomposition is complete at about 700/sup 0/C after 1000 hr. The minerals begin to decompose at a lower temperature in steam. Reactions among carbonates and silicates resulted in the release of CO/sub 2/ even under high CO/sub 2/ pressure.