Hydrogen bonding plays an important role in thermodynamic properties of polar fluids. Existing equations of state that include h-bonding cannot accurately predict the phase behavior for polar fluids. In the theories for h-bond-chain forming molecules, h-bonding strength is considered a constant at a given temperature and pressure. Infrared spectroscopy and ab initio calculations show that the h-bonding strength depends on whether or not the molecule was previously h-bonded at other sites. When all h-bond is formed between an already hydrogen-bonded species and it free species, the second h-bond has different energetic characteristics from the primary h-bond. In the case of 1-alkanol self-h-bonding, the equilibrium constant for the second h-bond is tell times that for the primary h-bond. This phenomenon called h-bond cooperativity was incorporated in a lattice-fluid-hydrogen-bonding equation of state. Calculations for pure 1-alkanols, show that the theory call be improved significantly by the incorporation h-bond cooperativity. Agreement with the phase behavior and spectroscopic h-bonding data improves using cooperativity, without any additional adjustable parameters. Heat of mixing calculations agree well with the experimental data.