The nitrogen bases in eight high-boiling crude oil distillates from four crude oils having different geological sources were characterized. Four basic compound types were found in all of the distillates--pyridine benzologs, diaza compounds, amides, and carbazoles. A chromatographic-infrared method was developed for the qualitative and quantitative determination of the major compound types. The data obtained using this method were compared with titration and total nitrogen data. This comparison demonstrated that the chromatographic-infrared method alone can be used to qualitatively and quantitatively analyze basic compound types in high-boiling petroleum distillates and that titration and total nitrogen data alone can be used to quickly estimate the kinds and amounts of major compound types in these distillates. The structures of the basic compounds were examined in detail using fluorescence, mass, and infrared spectrometry.