The oil sands in the Athabasca region of northeastern Alberta, Canada, represent a significant hydrocarbon resource that is currently exploited by mining, followed by separation of bitumen from sand using hot water flotation. This process generates large quantities of bitumen-contaminated tailings. Current research involves an assessment of whether the tailings ponds can ultimately be converted to biologically productive lakes, with one unresolved issue being the toxicity of the polycyclic aromatic compounds (PACs) that might be released from the tailings. In this paper, we have identified several polycyclic aromatic hydrocarbons in the porewater from oil sands mature fine tailings and have compared the responses of 17 PACs in the Ames and Mutatox genotoxicity assays. The Mutatox assay was unsuitable as a surrogate for the Ames test in this application; poor (50%) concordance between the two assays occurred because the mechanism of light emission in the Mutatox assay is uncertain, leading to positive responses that could not be unambiguously associated with genotoxicity. Benzo[a]pyrene equivalency factors (BEFs) in the Ames assay were determined for a large number of PACs, from this work and from literature data, to express the genotoxic potencies of environmental mixtures in terms of benzo[a]pyrene equivalent concentrations (BEQs). In the case of porewater samples obtained from the mature fine tailings, even extracts concentrated 10,000-fold were below the detection limit of 1 μg/L BEQ, consistent with the value of 0.14 μg/L calculated using BEFs of PACs identified in the porewater.