The hook method has been adapted for molecular spectra to allow a determination of the absolute oscillator strength of a band from measurements on a single hook near the band head. For the A² Sigma ⁺-X²II system of nitric oxide, the value f₀₀=(3.64+or-0.05)*10^-4 was obtained, in good agreement with previous measurements on the integrated absorption at high pressures. The behaviour of f₀₀ as a function of pressure was investigated at pressures up to 7 atm of nitric oxide and 35 atm of argon, but no variation was found. The relation between f₀₀ and the latest experimental value for the lifetime of the v'=0 vibrational level is discussed, using recent measurements for the variation of electronic transition moment with r centroid; the inconsistencies between these three sets of measurement prove to be considerably larger than the apparent experimental errors.