Abstract: Based on internal standards co-elution, retention indices comparison and molecular structure and chemical properties, a series of C₁-and C₂-alkylated dibenzothiophene isomers in oils and related sedimentary organic matters were firmly identified in this paper. The corresponding retention indices were also determined. This study corrected several compound peaks on mass chromatograms which were wrongly identified in previous publications. The elution order of all C₁ and C₂-dibenzothiophene isomers on GC column (HP-5MS) was systematically determined, and the distribution patterns of C₁-and C₂-alkylated dibenzothiophenes in petroleum and sedimentary organic matters were preliminarily discussed.