In the past decade, the large tailings pond (Mildred Lake Settling Basin) on the Syncrude Canada Ltd. lease near Fort McMurray, Alta., has gone methanogenic. Currently, about 60%–80% of the flux of gas across the surface of the tailings pond is methane. As well as adding to greenhouse gas emissions, the production of methane in the fine tailings zone of this and other settling basins may affect the performance of these settling basins and impact reclama- tion options. Enumeration studies found methanogens (105–106 MPN/g) within the fine tailings zone of various oil sands waste settling basins. SRB were also present (104–105 MPN/g) with elevated numbers when sulfate was avail- able. The methanogenic population was robust, and sample storage up to 9 months at 4°C did not cause the MPN val- ues to change. Nor was the ability of the consortium to produce methane delayed or less efficient after storage. Under laboratory conditions, fine tailings samples released 0.10–0.25 mL CH4 (at STP)/mL fine tailings. The addition of sul- fate inhibited methanogenesis by stimulating bacterial competition.