The acids in ten high-boiling crude oil distillates were characterized. Four major acidic compound types were found in all of the distillates--carboxylic acids, phenols, carbazoles, and amides. Three methods were used for the quantitative determination of the major acidic compound types. One method involved the use of a separation scheme by which compound types were separated and the percentage of each compound type was determined gravimetrically. The second and third quantitative methods utilized infrared spectrometry. The relative amounts of compound types in the various distillates could be determined using any of the three methods. (auth)