South Korea, Indonesia, and India. Most of Sudan's oil reserves are located in the Muglad and Melut rift basins in the south of the country. Oil fields in the south, such as those at Heglig and in the South Sudanese state of Unity, formerly part of Sudanese territory, are linked to the country's refineries via pipelines. The two largest oil pipelines are the Greater Nile Oil Pipeline, which travels 1,600 kilometres from the Unity oil field to Port Sudan on the Red Sea via Khartoum, and the PetroDar pipeline, which extends 1,380 kilometres from the Palogue oil field in the Melut Basin to Port Sudan. Crude oil from the Muglad Basin is known as "Nile Blend" and is refined at the Khartoum crude oil refinery. In 2006, the China National Petroleum Corporation upgraded the Khartoum refinery, doubling its capacity to . Oil from the Melud Basin is known as "Dar Blend" and is refined at the Port Sudan Refinery, which has a capacity of . In 2005, the Sudanese government contracted Petronas to build a new refinery at Port Sudan. Mining The mining industry contributed little to GDP until the discovery of commercially exploitable quantities of petroleum in the late 1970s offered hope that the sector would play an increased role in the economy in the future. Nonhydrocarbon minerals of actual or potential commercial value include gold, chrome, copper, iron ore, manganese, asbestos, gypsum, mica, limestone, marble, uranium, silver, lead, talc, tungsten, zinc, and diamonds. Employment The size of Sudan's labor force is difficult to determine because of the various definitions of participation in economic activity and the absence of accurate data from official sources. In rural areas, large numbers of women and girls engage in traditional productive occupations, but many probably are not included in calculations of the active workforce. More than 7.9 million people were employed in Sudan in 1989, according to an International Labour Organisation (ILO) estimate. In the early 1990s, the employment scene was exacerbated by the 1991 Persian Gulf War, which resulted in the return home of thousands of Sudanese workers who had been based in Kuwait and Iraq, leaving many of their possessions behind. Sudan's support of Iraq was also a factor in the departure of thousands of Sudanese workers from Saudi Arabia. By 2000, the total labor force of Sudan had grown to an estimated 12 million, of which the government counted 9.6