Characterization of the naturally occurring sulfur compounds in petroleum is of both theoretical and practical interest to petroleum chemists and geologists. This paper describes a systematic procedure for the concentration and identification of 35 individual thiols present in a Wasson, Texas, crude oil distillate boiling from 111°to 150°C. The procedures applied included distillation, alumina adsorption, chemical extraction, gas-liquid chromatography, microdesulfurization, and infrared spectroscopy. Many Cs and Ce thiols, not commercially available, were synthesized, and GLC retention times and infrared spectra of some of these are presented. The procedures described represent a systematic method of sulfur compound analysis that should have general application in petroleum studies.