We present high resolution (10−4cm−1) and high signal to noise ratio (2000) infrared lineshapes of CO perturbed by Xe, N2, and He in the intermediate regime from Doppler to collision broadening. It is found that the pressure broadened component of the lineshape cannot be fit by a Lorentzian lineshape. A speed dependent collisional width is required to fit the spectra, particularly when broadened by the larger Xe perturber. Based on the theory of Robertet al. [1992], a collision broadening lineshape model is derived, and we also include the effect of Dicke narrowing.