The distribution of dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes and their geochemical significance in the crude oils and source rocks from Niger Delta Basin have been investigated by gas chromatography-mass spectrometry. The dimethyldibenzothiophenes, 4-phenyldibenzothiophene, and benzo[b]naphtho[2,1-d]thiophene were the most abundant among the dibenzothiophene and its derivatives in the crude oils and rock samples. The phenyldibenzothiophene ratio-1 and phenyldibenzothiophene ratio-2 values in the rock samples were in the ranges of 0.08 to 0.67 and 0.20 to 2.53, respectively, while the 4-/1-methyldibenzothiophene, 4,6-/(1,4 + 1,6)-dimethyldibenzothiophene, 2,4,6-/(2,4,7 + 2,4,8)-trimethyldibenzothiophene, phenyldibenzothiophene ratio-1, and phenyldibenzothiophene ratio-2 values in the crude oils ranged from 1.52 to 5.82, 0.76 to 1.98, 0.77 to 1.22, 0.11 to 0.42, and 0.30 to 0.75, respectively. These values indicate source rocks and crude oils with mixed input of terrestrial and marine organic matter and deposited in lacustrine-fluvial/deltaic environments within immature to early mature stages. Four isomers of MDBT were also present in appreciable amounts in all the samples studied. The distribution patterns of MDBTs were generally observed in the order 4-MDBT > 2+3-MDBT > 1-MDBT in the crude oils and rock samples. The (1 + 4)-/(2+3)-methyldibenzothiophene ratio in the oils and rock samples ranged from 0.03 to 0.13 and 1.31 to 2.54, respectively. These values suggested source rocks with shale lithologies. A cross plot of (1+4)-/(2+3)-methyldibenzothiophene versus pristane/phytane measured on rock samples and crude oils from Niger Delta was used to study the influence of depositional environment and lithology on the distribution of the MDBT isomers. This cross plot clearly showed that the source rocks and crude oils studied have shale lithologies and were distinguished into lacustrine and fluvial/deltaic/freshwater environments and thus proposed in this study as a potential lithology and paleoenvironment indicator. This study showed that dibenzothiophenes, phenyldibenzothiophenes, and benzo[b]naphthothiophenes were effective in determining the origin, depositional environments, and thermal maturity status of crude oils and source rocks in the Niger Delta Basin, Nigeria.