ABSTRACT: Petroleum exploitation causes serious pollution to the semi-enclosed Bohai Sea (China) ecosystem. However, little is known about the influence of such pollution on the α- and β‑diversity of the bacterial communities or the in situ hydrocarbon biodegradation potential present in the surface sediments. This was explored using 16S rRNA gene-based terminal restriction fragment length polymorphism, along with alkane hydroxylase (AlkB) and soluble di-iron monooxygenase (SDIMO) gene-based clone libraries. α-diversity (Shannon-Weaver index) was negatively correlated with the BTEX (i.e. benzene, toluene, ethylbenzene, and xylene) and total nitrogen contents. β-diversity at the phylum/class level (class level for Proteobacteria) and terminal restriction fragment (T-RF) level responded differently to the abiotic factors. At a small to intermediate scale (21.4 to 142.2 km), β-diversity at the T-RF level was closely correlated with geographic distances, while at the phylum/class level, it was significantly influenced by environment heterogeneity. In total, 72.61% of the AlkB sequences were related to Gammaproteobacteria, including Alcanivorax and Marinobacter, while the SDIMO genes were similar to Phenol-2, Mmo, ThmA, PmoC and PrmA genes, with 72% of the sequences found being novel. The high SDIMO gene diversity might be related to the complexity of the hydrocarbon pollution (a mixture of phenol, methane, tetrahydrofuran, propene and propane) and demonstrates the existence of in situ hydrocarbon biodegradation potential. Information about the diversity of bacteria and the hydroxylases is helpful to guide the in situ bioremediation of petroleum pollution and protect ecosystem function in the Bohai Sea.