dic and neutral NSO compounds in a petroleum reservoir core extract were characterized by negative-ion electrospray（ESI）-Fourier transform ion cyclotron resonance mass spectrometry（FT-ICR MS）.Heteroatomic species were characterized according to their class（number of nitrogen,oxygen and sulfur heteroatoms）,degree of aromaticity ［double bonds equivalent（DBE）］,and carbon number.The results showed that 16 heteroatom class species were identified in the extract,including N1,N1O1,N1O2,N1O3,N1S1,N1S2,N2,N2S1,O1,O1S1,O2,O2S1,O1S2,O2S2,O3 and O4 heteroatom classes.The N1,N1S1,O2 and O2S1 class species were abundant.For N1 species,the most abundant compounds were carbazoles and benzocarbazoles.For N1S1 species,the most abundant compounds were carbazole flanked on a thiophene ring of benzothiophene（DBE=14） with C2-C8 alkyls.The most abundant O2 class species were 1- and 2-rings naphthenic acids,high abundant O2 species with DBE values of 5 and 6 were also identified.In addition,the O2S1 class species with DBE values of 7 and 8 were the most abundant.