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Densification of tailings slurries to mature fine tailings (MFT) is important in the oil sands industry for tailings inventory reduction, pore water recovery and tailings reclamation. The cause of methane release from the tailings pond of Shell Albian Sands (Albian) and the effects this process has on densification of Albian tailings was investigated. Citrate, added to tailings with polyacrylamide and hydrocarbon-diluent, was identified as the methanogenic substrate. Bacterial and Archaeal 16S rRNA gene sequences in Albian MFT were dominated by matches to Rhodoferax, some Clostridia and sulfate-reducing bacteria, and acetoclastic methanogens. Citrate-, diluent-, and polyacrylamide-amendments to Albian MFT did not cause a microbial shift over a 10-month laboratory incubation period. A potential pathway for microbial methane production in Albian MFT is proposed. Methane production and release from citrate-amended Albian MFT correlated to accelerated densification. Though diluent and polyacrylamide did not affect methanogenesis, they potentially affect gas bubble formation and release. / Microbiology and Biotechnology