Sulfur compounds are among the most important heteroatomic constituents of petroleum. These compounds are undesirable because they increase emulsion stability, cause corrosion, contaminate catalytic processes of refining, and determine color and odor of final products. Also, sulfur compounds play an important role in naphthenic corrosion, which occurs via chemical reaction of naphthenic acids with iron; sulfur limits corrosion through formation of a surface film of FeS, but this formation does not occur for all classes of sulfur compounds. Hence, their speciation is important. In this work, qualitative and semi-quantitative characterization of organic sulfur compounds were performed in two petroleum samples with no pre-treatment using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC x GC-TOFMS). Total sulfur content (ASTM D 4294) was 1.91% and 0.96%, on mass %, while degrees API was 33.1 and 19.6 for sample #1 and sample #2, respectively. Regarding cyclic sulfur compounds, one sample showed a total concentration of 60,363 mu g g(-1) of whole oil, while the other sample showed a total concentration of 4,740 mu g g(-1). Further, sulfides, disulfides, and thiols were detected only in sample #1; total concentration was 1,372 mu g g(-1). Thus, total concentration of all sulfur compounds for sample #1 was 61,735 mu g g(-1). These data illustrate the potential of the GC x GC-TOFMS technique for molecular characterization and semi-quantification, in this case sulfur speciation, of complex samples, such as petroleum. (C) 2014 Elsevier Ltd. All rights reserved.