Abstract We present high-sensitivity and high-spectral-resolution line-shape measurements of self-broadened CO (3←0) and (4←1) bands transitions measured using the frequency-stabilized cavity ring-down spectrometer. Ten of twelve investigated lines were measured for the first time. We have shown that the narrowing of the spectral lines should be taken into account to correctly determine their collisional broadening parameters. In our conditions line narrowing can be equally well described by Dicke narrowing or the speed dependence of collisional broadening. We compare line intensities measured with subpercent relative uncertainties and line positions to data available in the HITRAN spectroscopic database.