Oil sands mining operations in northeastern Alberta are rapidly expanding. Upgrading and extracting the bitumen from the sand requires large volumes of water generating large quantities of oil sands process water/materials (OSPM) which is high in organic content. Some of the major organic components found in OSPM include unrecovered bitumen, polycyclic aromatic compounds (PACs), naphthenic acids (NAs) and humic acids. Concerns of acute and chronic toxicity resulting from OSPM have led to provincial legislation preventing the discharge of OSPM into local water and mandating the reclamation of areas affected by oil sands mining. To date, OSPM is stored on lease in settling basins while the mining companies evaluate reclamation strategies. One of the reclamation strategies involves the use of wetlands constructed with differing amounts of OSPM and organic amendments such as peat. Currently, numerous wetlands, both natural and constructed, are present on oil sands leases. To determine the sustainability of these wetlands for reclamation, the assimilation and flow of carbon and nitrogen within the systems need to be defined. Stable isotope analysis can enhance this understanding. To effectively use stable isotopes in the field, there is the need to determine the changes in stable isotope values occurring from the microbial degradation of organic components such as NAs which contribute a significant portion to the dissolved organic carbon (DOC) in reclamation sites. This study examined the microbial degradation of commercial and oil sands derived NAs by oil sands derived microbial cultures. Changes in stable isotopes values in the biomass (δ13C, δ15N), DOC and dissolved inorganic carbon (DIC) (δ13C) arising from degradation of the DOC were tracked in both static and semi-continuous tests. Utilization of commercial and oil sands derived NAs resulted in minimal change of the DOC stable isotope values. The biomass was 13C enriched for both the commercial