A process is disclosed for the separation of carbon dioxide and sulfide gases from oil shale retort off-gases, coal gasification off-gases, oxygen fire-flooding or carbon dioxide miscible flood enhanced oil recovery off-gases for recycle to a retort, gasifier or petroleum reservoir or alternately delivery to another process. The process separates the off-gases into an essentially sulfur-free fuel gas and an acid gas for recycle to such a retort, gasifier or reservoir wherein the off-gas is compressed if necessary and cooled to separate the two streams, the acid gas is expanded in an auto refrigeration step to provide the necessary process refrigeration and the acid gas is then recycled to such a retort, gasifier or reservoir. In the oil shale retorting and coal gasification applications, the gas' sulfur constituents are sorbed on spent oil shale particles or coal ash.