Sudan claims Heglig's oil fields, which account for about half of the nation's oil production, and Sudanese President Omar al-Bashir had vowed to "never give up" the disputed region.

CNN: South Sudan says it is withdrawing from disputed oil region

Sudan's oil industry suffered when fighting in Heglig forced a halt to oil production in those fields, which account for about half of the country's production of 115, 000 barrels a day.

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Sudan's oil industry suffered further when fighting in Heglig forced a halt to oil production in those fields, which account for about half of the country's entire production of 115, 000 barrels a day.

CNN: South Sudan accuses Sudan of aerial, ground attacks

However, these geochemical investigations tended to be focused on the impacts of mining and mineral processing at a national level and in specific mining fields without taking account of the overall impact on larger hydrological and environmental domains across the continent.

UNESCO: EARTH SCIENCES FOR SOCIETY

Iraq has the world's third-largest proven oil reserves, with 115 billion barrels, of which the fields up for auction account for about 43 billion barrels.

BBC: Oil companies reject Iraq's terms

Meanwhile, production is falling in the mega-fields in western Siberia that account for the majority of Gazprom's production.

ECONOMIST: Russian gas and Europe