Detailed compositional analysis of nine crude oils and their saturate, aromatic, resin, and asphaltene fractions were carried out by elemental analysis and Fourier transform infrared spectroscopy. The crude oils had a broad range of physicochemical properties. The largest difference in composition was found in the asphaltene fractions of the oils, followed by the resin fractions. These fractions had significantly higher abundance of oxygen and nitrogen heteroatoms than the saturate and aromatic fractions. Furthermore, the lightest crude oils had the highest oxygen content in the asphaltene fraction, while it was the highest in the resin fraction for the heaviest oils. Partial least-squares regression models suggested that the total acid number was primarily associated with carboxylic acids in aliphatic structures and that high abundance of nitrogen and oxygen particularly in the resin fraction enhanced the total base number. It is believed that the detailed structural information provided here will help to improve the understanding of the interfacial properties of the crude oils.