A semiquantitative derivatization/NMR method for analysis of sulfur compounds in petroleum is described. The method relies an the conversion of sulfur compounds to their corresponding methylsulfonium salts following by C-13 NMR analysis. The signals of the methyl carbons are then matched to those of the model sulfoniun salts. The initial results using a high sulfur crude petroleum are presented. The C-13 NMR spectra of the S-methylated crude are consistent with a large proportion of thiophenic structures in this crude. Dibenzothiophene-type, benzonaphthothiophene-type, and naphthothiopene-type structures are tentatively identified in the crude. Quantitative C-13 NMR analysis-of the methylated crude shows that about 75-80 % of the sulfur functions in the crude are methylated to methylsulfonium salts.