High-resolution Fourier transform spectra of H 2 O-air mixtures have been measured at 296, 742, and 980 K for total pressures of 0.5 and 1.0 atm in the region of the n 2 band. From these recordings, airbroadening coefficients have been determined for the doublet lines with K c ΒΌ J: From these data and previous experimental determinations, line-broadening parameters gΓ°TΓ are obtained at all three temperatures for the doublet lines from J ΒΌ 0 up to 16. These values are then used to deduce the temperature-dependence exponent n such that gΓ°TΓ ΒΌ gΓ°296Γ Γ Γ°296=TΓ n : The values of n obtained using the two elevated temperatures are consistent and show that line widths decrease with T for small J-values Γ°n % ΓΎ0:8Γ; are almost temperature independent on T for J % 10; and increase with T for high J lines (n % Γ0:3 for J % 15). This original result, which confirms theoretical predictions made about 15 years ago with a semi-classical approach (J. Chem. Phys. 86 (1987) 144), is analyzed here using an improved version of the model. Comparisons between measured and computed widths show that calculations cannot correctly reproduce the experimental results at all temperatures simultaneously. This failure is attributed to the use of an inappropriate interaction potential and to the very strong dependence of the broadening gΓ°vΓ on the relative velocity v for high J lines. This strong variation of gΓ°vΓ raises the question (which is discussed here) of what calculated quantity is to be compared with measured values (i.e. gΒ½ vΓ°TΓ; Β½gΓ°vΓ Γ°TΓ; or some other more complex mean to account for the velocity averaging of the spectral profile itself?). Nevertheless,