As oil plumes percolate and mix with groundwater, the bulk concentration and chemical composition of petroleum-derived, non-volatile dissolved organic carbon (NVDOC) is altered via dilution and biodegradation pathways. Using the benzenepolycarboxylic acid (BPCA) method, we revealed unique mixing patterns for the condensed aromatic carbon fraction of NVDOC along an oil plume transect in Bemidji, Minnesota (USA). Samples were collected from the oil body to the toe of the plume in the direction of groundwater flow. Concentrations of NVDOC and BPCAs decreased by ~95% and ~80%, respectively, along the plume transect. However, the proportion of condensed aromatic carbon to NVDOC generally increased from 1% to 7% along the plume transect. Deviations from the observed trendline at the toe of the plume (i.e. same site, different well depths) may indicate mixing with background groundwater. We recently incorporated BPCA-specific stable carbon isotopic analysis to differentiate condensed aromatic carbon contributions from the oil versus native groundwater. Taken together, these findings suggest BPCAs may be used as a conservative tracer for petroleum products in oil-affected groundwaters because they persist at distal plume locations, even where residual petroleum hydrocarbon concentrations are low and/or oil-derived NVDOC is severely altered via biodegradation. Results of this work expand our understanding of oil plume stability and environmental persistence. New applications for the BPCA method include sourcing and quantifying petrogenic and hydrothermal carbon inputs to inland waters and the deep ocean.