The IR spectrum of the ν3 band (4.85 μm) of gaseous OCS has been investigated along the liquid–vapor coexistence curve for temperatures varying from 268 to 358 K and densities up to 80 amagat. Measurements of integrated intensities are also reported at room temperature.The dipole moment autocorrelation functions (ACF) deduced from the spectra of compressed OCS are analyzed in terms of a collisional model derived from the impact approximation and in terms of Gordon M and J diffusion models developed classically as well as the semi-classical M diffusion model. For the collisional model which implies uncorrelated rotational levels, a discrepancy between predicted and observed ACF's is noticeable from about 15 amagat. The M and J diffusion models agree well with the experimental ACF's only up to 40 amagat.