The Burgan field is an oil field situated in the desert of southeastern Kuwait. Burgan field can also refer to the Greater Burgan—a group of three closely spaced fields, which includes Burgan field itself as well as the much smaller Magwa and Ahmadi fields. Greater Burgan is the world's largest sandstone oil field, and the second-largest overall, after Ghawar. The Burgan Field is located on the coast of the Persian Gulf which played a huge part in the creation of this prominent reservoir formation many million years ago. Discovery and geology A natural surface oil seep above the Burgan field was known to humankind since neolithic time, bituminous material from a reed boat discovered in As-Sabiyah/North Kuwait and dated 5000 BC have been traced back to this seep. The subsurface reservoirs of the Burgan oil field were discovered in February, 1938. The US and UK-owned Kuwait Oil Company began commercial oil production at Burgan in 1946. The Greater Burgan, a wider area around Burgan, is the world largest sandstone (clastic) oil field with the total surface area of about 1000 km2. It includes three producing subfields: Burgan itself (500 km2), Magwa (180 km2) and Ahmadi (140 km2). The Burgan field's structure is an anticlinal dome having an elliptical shape and transected by numerous radial faults. Both Magwa and Ahmadi are located on smaller, subsidiary domes north of Burgan. The oil is contained in the four main horizons of Cretaceous age: Wara (sandstone), Mauddud (limestone), Burgan Third Sand (3S) and Burgan Fourth Sand (4S). Burgan Third Sand is in turn subdivided into Third Sand Upper (3SU), Third Sand Middle (3SM) and Third Sand Lower (3SL). Historically the production has come mainly from the 3SM unit. By 1992 the second and third sand units had been swept by water. Stratigraphy The Burgan Oil Field is made up of three main subsurface structures known as the Magwa, Ahmadi, And Burgan formation. The deeper reservoirs, namely the Lower Cretaceous Ratawi and Minagish limestones and the Jurassic Marrat Formation also contain significant oil reserves but are less substantial. The Magwa and Ahmadi formation are separated from the Burgan formation by a normal fault cutting horizontally down through the whole structure. This is known as the Burgan Graben. The role of tectonic stresses that have affected this region in Mesozoic and Cenozoic times also play a part in much of the faultings seen in the formation.