Four different crude oils-Arab Heavy (AH), Arab Beni (AB), Alaskan North Slope (ANS), and San Joaquin Valley (SJV)--were characterized by separating the crudes into compound classes by two different fractionation methods--extrography (ext) and asphaltene precipitation followed by extrographic isolation of the resins (ppt + ext). The fractions derived from these two methods of separation were characterized and compared in order to determine the most, complete and discriminating compositional analysis for subsequent use in studies concerning the stability of emulsions or sludges which are produced by these crudes in refinery processing. The resin and asphaltene fractions are of primary interest due to their polar, surface-active nature, the central role these fractions play in stabilizing emulsions and sludges, and their resulting influence on crude processability. Preparatory-scale separations were developed and utilized to provide sufficient amounts of the polar fractions of these crudes for further studies. The H/C ratio and concentrations of S, N, and O as well as V and Ni contents were determined for each of the crudes and their respective fractions. The results of this investigation also provided useful information regarding the H-bonding capacity (as gauged by the functional group types and content) and aromaticity of the polar fractions of these particular crude oils. The polar functional groups and carbon types were identified and quantitated by FTIR and C-13 NMR spectroscopy. FTIR analysis also provided an indirect measure of the polarity of substituent groups attached to the aromatic core of these molecules when comparing the results of the integration of the aromatic C=C stretch with the aromaticity as measured by C-13 NMR. analysis. Both the H-bonding capacity and the aromaticity are considered to play a central role in determining the solubility of asphaltenes in the crude medium which in turn has a significant effect on the emulsifying potential of the crude oil. In the comparison of the two fractionation methods, the resin and total asphaltene yields were very similar for most of the crude types; however, the characteristics of these polar fractions varied considerably in all the crudes depending upon the method used to isolate them. There was strong evidence to support the prevailing sentiment that the fraction which is coined "asphaltenes" is greatly influenced and defined by the very method utilized to isolate this fraction. When considering and analyzing the characteristics of the polar materials in their totality (i.e., resins + asphaltenes), these materials were very similar in nature regardless of the fractionation method used to isolate them. However, irreversible adsorption of asphaltenic components (up to similar to 0.8 wt % of whole crude) on the silica gel does occur when employing the extrographic technique. Thus, the ppt + ext fractionation method appears to be the simplest and most robust method to provide further understanding of the mechanisms which govern the stability of emulsions produced from different crude types.