Hydrogen-bond cooperativity is an effect when hydrogen bonding is influenced by the previously formed hydrogen bond on the molecules. Using Fourier-transform infrared spectroscopy, we have measured the extent of self hydrogen bonding in 1-hexanol and 1-pentanol dissolved in n-hexane. Conventional theories without hydrogen-bond cooperativity, such as the statistical-association-fluid theory, lattice-fluid-hydrogen-bonding theory and associated perturbed-anisotropic-chain theory, cannot represent the experimental data accurately. The extended lattice-fluid-hydrogen-bonding theory that includes hydrogen-bond cooperativity agrees well with the experimental data. Study suggests that the equilibrium constant for the second hydrogen bond on 1-alkanol molecules is 10 times larger than that for the first hydrogen bond formation. Hence, strong hydrogen bond cooperativity exists in 1-alkanol self association. Equations of state dealing with 1-alkanol mixtures need to be modified to account for this strong hydrogen-bond cooperativity.