The Peng-Robinson equation was incorporated with the monomer-dimer chemical equilibrium model through two different approaches to result in two different equations of state. The reformulated Peng-Robinson equations were used to represent the vapor pressures and liquid densities of selected carboxylic acids ranging from acetic acid to octanoic acid. The equations were also used to represent the vapor-liquid equilibria of selected carboxylic acid + hydrocarbon binary mixtures. The capabilities of different association model-incorporated equations of state were compared. The results show that in general the reformulated Peng-Robinson equations are superior to the Wilson equation and the other equation-of-state (EOS) models. (c) 2006 Elsevier B.V. All rights reserved.