Revenue from Sudan's oil may be being unfairly shared out threatening a north-south peace deal, a report by campaign group Global Witness says. It says discrepancies in figures given by the north and those of the Chinese firm operating the oilfields may mean the south is being seriously underpaid. Following the 2005 agreement to end 22 years of civil war, the north and south are meant to share the revenue. Southern officials have accused the north of withholding oil money before. Global Witness has called for greater transparency in the oil industry, which is effectively run by the north, and accounts for 98% of the budget of southern Sudan. "Unless the government of southern Sudan and Sudanese citizens can verify that the revenue sharing is fair, mistrust will grow and the peace agreement could be jeopardised," said report author Rosie Sharpe, AFP reported. It says there are the north was using lower figures than the Chinese company which operates most of the oil blocks. The study "raises serious questions about whether the revenues are being shared fairly", Global Witness said. "Mismatches of this magnitude represent potentially massive sums of money." Global Witness said it found a difference of between 9% and 26% in the government's estimates and the company's estimates. Millions owed The group said a total undercount of 10% since 2005 would mean "the southern government would be owed more than $600m (£365m)". Ms Sharpe told Reuters news agency that the oil company could be overstating figures - "although the figures do come from their annual report, an official publication of a multi-billion dollar company". If government figures are not right, the revenue allocated to the south will not be right either, the report says. Global Witness says the only block located entirely in the north, and therefore not subject to revenue sharing, is the only one where the figures approximately match. The group is careful not to accuse Khartoum of cheating the south. "Our findings do not necessarily mean that Khartoum has cheated the south out of money, but they do highlight the need for transparency," Ms Sharpe said. Although southern officials have accused the north of withholding oil money in the past, the BBC's James Copnall in Sudan says they are frequently accused of corruption too. Source: BBC