The impact of severe biodegradation on the molecular and stable (C, H, N, S) isotopic compositions of oils in the Alberta Basin, Canada.

Highlights: [•] We investigated the molecular and isotopic compositions of biodegraded oils from the Alberta Basin. [•] Alberta heavy oils show increasing biodegradation from top to bottom of the oil columns. [•] The level of oil biodegradation varies regionally in the basin, ranging from PM2 to PM10+. [•] S and N isotopic compositions of the heavy oils are not affected by severe biodegradation. [•] The S and N isotopic compositions of biodegraded oils are indicative of the primary oil charge. [Copyright &y& Elsevier]