n-Alkanes are ubiquitous and useful biomarkers in the biogeochemistry field. Their carbon isotope com-position in sedimentary organic matter is therefore of particular importance for inferring their origin. The commonly used technique for d 13 C determination, isotope ratio mass spectrometry (IRMS), gives access to the isotope composition of n-alkanes at the molecular level, but does not provide information on their intramolecular isotope distribution. Here, we evaluate the potential of isotopic 13 C nuclear magnetic resonance (NMR) spectrometry for the determination of the intramolecular isotope composition of long chain n-alkanes (C 11 –C 31). The relative isotope composition of the three terminal carbon positions can be determined with a precision of 1.2‰ or better. The results from commercially available samples show that (i) the intramolecular 13 C isotope distribution is opposite between odd and even numbered n-alkanes in the C 16 –C 31 range and (ii) those in the C 11 –C 15 range show a 13 C depletion of ca. 12‰ in the methyl position and no difference between odd and even numbered compounds. The results are consis-tent with a biological origin of heavy n-alkanes whereas lighter ones are proposed to originate from abiogenic degradation such as thermal cracking. Overall, although only partial intramolecular 13 C patterns are obtained, the approach appears as promising tool in petroleum exploration and in the bio-geochemistry field.