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This manuscript describes the first application of ultrafast-laser-absorption spectroscopy (ULAS) to characterizing high-pressure (up to 40 bar), multi-phase combustion gases. Single-shot measurements of temperature and CO were acquired at 5 kHz in AP-HTPB propellant flames with and without aluminum. An ultrafast light source was used to produce broadband pulses of light near 4.96 𝜇m at a repetition rate of 5 kHz and a high-speed mid-infrared imaging spectrometer was used to image the pulses across an 86 nm bandwidth with a spectral resolution of 0.7 nm. Measurements of temperature and CO concentration were obtained by least-squares fitting simulated absorbance spectra of CO to measured spectra. A system of corrective optics was used to diminish the e˙ect of beam steering during high-pressure experiments, greatly increasing the pressure capabilities of the diagnostic. The diagnostic was used to characterize AP-HTPB propellant flames in an argon bath gas at pressures of 1, 10, 20, and 40 bar. An aluminized AP-HTPB propellant was also characterized at 10 and 20 bar to demonstrate that ULAS can provide high-fidelity measurements in particulate-laden flames. The results demonstrate that ULAS is capable of providing single-shot temperature and species measurements at high pressures with 1-𝜎 precisions less than 1.1% and 3% for temperature and species respectively, despite non-absorbing transmission losses in excess of 90%.