The accuracy of pure rotational coherent anti-Stokes Raman spectroscopy (CARS) temperature measurements was investigated using O2, N2 and synthetic air for comparison. These measurements were performed in a high-pressure cell for pressures between 0.1 and 15 MPa. The cell temperature was varied between 300 to 700 K. The temperature values deduced from the pure rotational CARS S-branch of O2 are in good agreement with the reference thermocouple reading. For the temperature and pressure range investigated, the accuracy for O2 measurements was better than that obtained for N2 and synthetic air. Copyright © 2003 John Wiley & Sons, Ltd.