O2-broadening coefficients have been measured for 29 lines of C2H2 at 173.2 K in the P and R branches of the nu5 band near 14 µm, using a tunable diode-laser spectrometer. The collisional widths obtained by Rautian profiles closely fitting the measured spectral shape of the lines are slightly larger than those derived from Voigt profiles. The broadening coefficients are compared with results calculated from a semiclassical theory, performed by considering, in addition to electrostatic interactions involving the hexadecapole moments of C2H2 and O2, the atom-atom Lennard-Jones model. By comparing broadening coefficients at 297 and 173.2 K from a simple power law, the temperature dependence of these broadenings has been determined both experimentally and theoretically. Copyright 1999 Academic Press.