Abstract Huge hydrocarbon potential still exists in Iran, even after prolific production for many decades. Currently, Iran is operating about 28 drilling rigs (23 of them onshore) and is producing about 3.6 million barrels of oil per day and about 3 trillion cubic feet of gas per day from approximately 1200 wells in 39 fields. Since oil was discovered at Masjid-i-Suleiman in 1908, exploration has extended onshore and offshore to several provinces and regions of southwestern Iran. Oil production from the Zagros fold belt dominates Iranian hydrocarbon production. Zagros reservoirs are in Jurassic, Cretaceous, and Tertiary carbonates and siliciclastics. Despite decades of exploration and production, future exploration and field- development opportunities appear to abound, now aided by new technologies and tools.

The structural style of the southeastern region of the Dezful Embayment (Zagros fold-and-thrust belt) was defined through the interpretation of satellite images, field surveys, well stratigraphy, and magnetotelluric and seismic profiles. The compressional setting of the area derives from the last phases of Cenozoic continental collision between the Arabian Plate and Eurasia. The shortening affected an ∼13 km thick sedimentary succession comprising Proterozoic units (Hormuz Formation?), Cambrian to Early Miocene platform sediments (mainly carbonates), the Gachsaran evaporites, and Mio-Pliocene foredeep clastic deposits. Although in the Dezful Embayment there is no evidence for outcropping Hormuz salt, the structural features of the area (the style of folds, their lack of consistent vergences, the low-angle tectonic taper) suggest the existence of a lower ductile detachment level of possible great thickness and low frictional resistance. The rounded folds in the carbonates are forced folds detached over a deep ductile level, subsequently faulted with progressive deformation by characteristic steepening up reverse faults. Second-order asymmetric folds affecting the limbs of the main structures indicate a flexural slip mechanism of folding in a multilayered and mechanically heterogeneous (carbonates and shales) succession. The Gachsaran Formation is deformed by shorter, strongly disharmonic folds and thrusts, and acted as a decoupling level for the overlying folds, whose synclines often directly overlie the carbonate anticlines. A regional restored cross section indicates a shortening of 11.5% in the area. The involvement of the crystalline basement in thrusting and the deep structural style of the area are discussed in terms of earthquake mechanisms, focal depths, structural analysis, and stratigraphic considerations.