Abstract: Structural parameters, such as ¹ H NMR spectrum, hydrogen and carbon atom contents,for 20 petroleum fractions from two crude oils were determined by using nuclear magnetic resonance (NMR) spectroscopy and elemental analysis.The thermochemical properties,combustion enthalpy and vaporization enthalpy of these fractions were also measured.Each average molecule in the petroleum fraction was supposed to be composed of five simple groups,CH ₃,CH ₂,CH,ACH and C,and the group number was calculated respectively on the basis of the results of ¹ H NMR determination and elemental analysis.Combustion enthalpies and vaporization enthalpies of the investigated fractions were then predicted by the group contribution methods originally for pure organic compounds in the literature.The predictive results were in reasonable agreement with the experimental data.