A laser absorption diagnostic technique, probing the mid-infrared vibrational bands of (CO)-C-12-O-16 and (CO)-C-13-O-16 near 4.9 mu m, was developed for sensitive multi-isotopologue temperature and concentration measurements in high-temperature gaseous systems. Transitions in each of the P-branches of the fundamental bands of (CO)-C-12-O-16 and (CO)-C-13-O-16 were chosen based on absorption linestrength, relative spectral isolation, and temperature sensitivity. Five total rovibrational transitions are spectrally-resolved over a similar to 1.2 cm(-1) domain using a 50 kHz triangle scan function with a distributed-feedback quantum cascade laser, yielding a 100 kHz effective measurement rate of both isotopologues and respective temperatures, independent of mixture composition. In addition, relevant broadening parameters for the P(0,22) transition of (CO)-C-13-O-16 near 2007.8767 cm(-1) were measured to enable higher time resolution (> 1 MHz) measurements using fixed-wavelength methods. Time-resolved multi-isotopologue thermometry performance was validated in a shock tube over a range of temperatures (1100-2400 K) relevant to combustion kinetics investigations. The technique is utilized in shock-heated oxidation experiments with isotopically labeled fuel mixtures, simultaneously measuring both carbon monoxide isotopologues throughout the reactions. To the authors' knowledge, these results demonstrate the first use of carbon isotope labeling with laser absorption spectroscopy to observe distinct competitive oxidation among different fuel components. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.