Abstract: Tectonic evolution and reservoir forming conditions of the Rio Muni Basin, Equatorial Guinea are studied in this article using the methods of prototype basin analysis, seismic data interpretation and petroleum geological analysis. The results show that the tectonic evolution of the region can be divided into three stages:rifting, transition-drifting and passive continental margin formation. The basin is mainly filled with Cenozoic and Mesozoic sediments. There are two suites of Cretaceous hydrocarbon source rocks developed:lacustrine argillutite during the rifting stage and marine argillutite during the transition-early drifting stage. Hydrocarbon accumulation is mainly related to salt structure and gravity sliding. Oil and gas are mainly accumulated in the middle zone with excellent reservoir forming conditions, which is low in exploration degree.