There is growing interest in optimising biogenic coal seam methane generation; however, relatively little is known about the microbiology of coal. To begin to address this deficiency, the biodiversity of a microbial community within a deep coal gas reservoir was investigated using the Amplified Ribosomal DNA Restriction Analyses (ARDRA) method. Additionally, a cultured subset of organisms from this community was examined for the ability to produce methane. ARDRA revealed that this community included both bacterial and archaeal lineages. The bacterial community was dominated by proteobacterial and Firmicutes taxa, though one actinobacterial taxa was also detected. This study is the first report of methanogenic archaea in an Australian coal seam gas reservoir. Cultures derived from the microbial community in the groundwater were able to produce methane from yeast extract and H₂/CO₂, but did not produce methane from coal. The ecological and physiological implications of these data are discussed.