The Cretaceous rudist-bearing carbonates of the Arabian Gulf region are proven exploration targets for hydrocarbons and form the reservoirs of a number of giant fields, including Bu Hasa, Fateh, Fahud, Idd El Shargi, Rumaila, Shaybah, and Shah. Rudist buildups occur in three principal formations: (1) Aptian Shuaiba, (2) Cenomanian Mishrif, and (3) Maastrichtian Simsima. A regional subaerial unconformity marks the upper boundary of each of these formations.

Associated with the rudists that dominate the Shuaiba Formation are calcareous algal crusts, foraminifera, and echinoid plates, which accumulated in mudstone, packstone, and carbonate sands. These rudists are mainly caprinids, with a lesser number of caprotinids, monopleurids, and requienids, deposited in a normal-marine shallow-shelf setting.

The Mishrif Formation contains mollusk fragments, bioclastic packstones to grainstones, miliolid and nonrudist bivalves in muddy limestones, and rudist (mainly radiolitids and caprinids) conglomeratic floatstones, with fragmented rudists mixed with wackestone lithoclasts. The Mishrif sediments accumulated as a progradational, low-energy leeward margin formed in marginal slope, shoal-backshoal, and lagoonal settings.

The Simsima Formation consists of bioclastic grainstone to packstone, and dolomitic lime mudstones to wackestone. These are rich in bioclastic grains (Loftusia, rudist and rudist debris, coral, and foraminifera) deposited on a restricted to semirestricted shallow-marine shelf that was exposed to moderate energy conditions.

The excellent reservoir porosity and permeability of the rudist deposits and their associated sediments are the products of primary and secondary diagenesis. Freshwater leaching during post-Aptian, post-Cenomanian, and post-Maastrichtian erosion enhanced the secondary moldic porosity. Fracturing locally improved porosity and permeability. Other porosity types that occur include interparticle, intraparticle, vuggy, growth framework, shelter, intercrystalline, and karstic.

Because of their favorable depositional and postdepositional conditions, the Cretaceous succession of rudists in this region contains many giant oil fields.