In the past decade, biogenic methane production in the fine tailings pond of Syncrude Canada Ltd. has increased markedly. This study addressed the questions: what started methanogenesis; what are the substrates for methanogenesis; and how long will methanogenesis occur? All the fine tailings produced methane but the organic compounds leading to methanogenesis could not be identified. Phenol, p -cresol and m -cresol stimulated methanogenesis but o -cresol, toluene, phenanthrene, anthracene, hexadecane and naphthenic acids did not. Mixtures of the naphthenic acids were toxic to the consortium. In the fine tailings, methanogens and sulfate-reducing bacteria co-exist but the precise relationship between the two populations could not be determined. Bacterial competition stimulated by the addition of nitrate and sulfate inhibited methanogenesis. Fine tailings samples produced between 0.10 to 0.25 mL CH 4 /mL tailings in batch methanogenesis monitored for over a year. Methanogenesis was a finite process and slowed after substrates were depleted.