To process and use the heavy ends of petroleum effectively, the development of suitable separation and characterization procedures not currently available was required. A systematic procedure was developed by the Bureau of Mines using such techniques as isothermal and molecular distillation, chemical treatment, silica-alumina gel chromatography, gel permeation chromatography, and spectrometry. Using these techniques, the Bureau achieved a detailed separation and characterization of a 370 to 535 C distillate from Gach Saran, Iran, crude oil. Such a systematic procedure and the semiquantitative data resulting therefrom should be of value in selecting feedstocks and in optimizing petroleum processing operations.