Oil hosted in a rock taken from a seep exposed by a road cut in north-central Peru was studied by geochemical means. The oil is classified as heavy paraffinic (waxy) by liquid chromatography. The oil appears to be highly mature, showing evidence of chemical and/or biological degradation. This is further supported by relatively high yields of polar fractions (resins and asphaltenes), partial depletion of n-alkanes below C-16, and a relative enrichment of isoprenoid hydrocarbons. The n-alkane distribution obtained by whole-oil gas chromatography (GC) also points to mature, waxy oil. Pristane/phytane and isoprenoid ratios suggest that Type II kerogen deposited in low-oxygen (dystrophic) environment was likely the source of the oil. Biomarker fingerprints of the saturate fraction obtained by gas chromatography-mass spectrometry (GC-MS) and other characteristic ratios indicate the high level of thermal maturation of the oil and suggest that the oil was derived from a clay-rich source rock rich in bacterial-derived organic matter deposited in suboxic conditions. Aromatic biomarker data confirm the high level of thermal maturity of the oil and point to a mixed shale/carbonate source rock deposited in a sulfate-poor marine environment. The parent oil most likely has a pre-Cretaceous source due to the absence of 18 et (H) oleanane and the fact that the C-28 alpha beta beta/C-29 app steranes and the C-28 alpha beta beta/C-29 COP sterane vs. C-27 alpha beta beta/C-29 alpha beta beta sterane ratios are both comparable to values reported for oils derived from the Jurassic Pucara Formation source rock in the nearby Maration Basin. (C) 2012 Elsevier B.V. All rights reserved.