In the current Zagros Fold Belt of Iran and in its contiguous offshore, five petroleum systems caused an impressive gathering of oil and gas fields that represent some 8% and 15% of global oil and gas reserves, respectively. Almost all the oil fields are located in the relatively small Dezful Embayment, which extends over 60 000 km 2 , whereas most of the gas fields are concentrated in Central and Coastal Fars and in the contiguous offshore area. This paper describes the functioning of the various petroleum systems through time, each petroleum system having its own specificity, and reconstructs the succession of events that explains the current location of the oil and gas fields and the reservoirs in which oil and/or gas accumulated. In addition to the classical description of the petroleum systems (distribution and organic composition of the source rocks, evolution of their maturity through time, geometry of drains and reservoirs, and trap availability at the time of migration), the influence of tectonic phases (Acadian, Hercynian, Late Cenomanian to pre-Maastrichtian, and Late Miocene to Pliocene Zagros phases) on the various systems are discussed. As the time of oil and/or gas expulsion from the source rocks is necessary to reconstruct migration paths and to locate the traps available at the time of migration, extensive modelling was used.