In this work, the linear isotherm regularity equation of state (LIR EoS) has been extended to predict the molar density of long chain primary and secondary amines, and esters and also the binary and ternary mixtures containing different functional groups. Each of these organic compounds has been assumed as a hypothetical mixture of methyl, methylene, and a functional group. Then, the LIR EoS has been modified for such a hypothetical mixture (MLIR EoS). Propane, n-butane, cyclohexane, 1-pentylamine, 2-aminobutane and n-butyl acetate have been used to investigate the contribution of the different segments in the new EoS parameters. The calculated parameters along with the MLIR EoS have been used to calculate the molar density and other thermodynamic properties of different pure compounds and their binary and ternary mixtures. A wide comparison has been made with some other EoSs and correlations. The results show that the MLIR EoS gives better results than other methods in accord with experimental data. (C) 2011 Elsevier B.V. All rights reserved.