Stable isotope ratio measurements of carbon atoms using isotope ratio mass spectrometry (IRMS) can be an effective tool for quantifying biogenic carbon in co-processed fuels, with results approaching the precision and accuracy of accelerator mass spectrometry (AMS). The lower cost of an IRMS may enable deployment to refineries, improving access and analysis turnaround times (= 2 hours), and, by extension, provide data that can allow process optimization to maximize renewable carbon in desired refinery products. This project explored integration of chemical separation with IRMS analyses to enable highly detailed tracking of biogenic carbon into fuel product streams separated by boiling point range, chemical class, or specific compound. Forty-nine fuels and fuel components of fossil and biogenic origin, spanning gasoline and diesel boiling ranges, were received from three refiners and were analyzed for their d13C values via IRMS. Results spanned a d13C range from ca. -10‰ to -44‰ and did not necessarily reflect values expected from commonly accepted ranges associated with materials derived from sustainable materials (e.g., C4 or C3 plants, as well as animal-based products derived from these pathways) or from petroleum. Fuel-like standards were developed and tested using a direct-injection Elemental Analyzer IRMS (EA-IRMS) for liquid fuels. This method was compared with the published method, yielding statistically similar results.