The National Iranian South Oil Company (NISOC) (Persian: شرکت ملی مناطق نفتخیز جنوب ایران‎‎), is a government-owned corporation under the direction of the Ministry of Petroleum of Iran, and operates as a subsidiary of National Iranian Oil Company. NISOC is incorporated 1971, in Masjed Soleyman, Khouzestan as Oil Service Company of Iran (OSCO). Currently NISOC is Iran's biggest oil producer, and the company is active in a land area more than 400,000 km² with headquarters in Ahvaz, and other five subsidiaries. NISOC is producing about 83% of all crude oil and 17% of natural gas produced in Iran and ranks as the Iran's largest oil company National Iranian South Oilfields Company, through its subsidiaries, produces crude oil, gas, and liquefied gases. The company also provides overhaul and maintenance of installation, equipment, and machines of gas turbines used in the petroleum industry. In addition, it offers repair and completion of oil and gas wells using special rigs, machines, and equipment; and engages in the repairing, fishing, rehabilitation, and completion of wellhead and inner well equipment using mobile core pipes. Further, the company provides petroleum transportation and logistics services, which include light urban and road transportation, heavy transportation, and special drilling rigs in the operation, services, project, and oil resources preservation sectors. Furthermore, it offers petroleum welfare services, such as planning and execution of non-industrial activities. NISOC in charge of onshore oilfields in southern Iran (like Ahwaz Field, Gachsaran, Marun, Bibi Hakimeh, Mansouri, Rag Sefid and Aghajari) and focuses on onshore upstream activity in the province of Khuzestan, Bushehr, Kohgiluyeh and Boyer-Ahmad, Lorestanand Ilam. As Khuzestan is the main oil and gas-producing province, this entity is among the most significant in the NIOC subsidiaries.