(CNN) -- A report released Thursday calls for more transparency over Sudan oil revenues to avoid conflict as the nation prepares for a vote that could see it split into two.
"With a referendum on independence for southern Sudan just days away, oil sector transparency is now more important than ever to preserving the fragile peace between north and south," Global Witness said in its report.
Southern Sudan is scheduled to start voting Sunday on whether to become an independent country or remain part of Sudan. At stake in the vote are Sudan's massive oil reserves, found mostly in the south, but still controlled by the government in the north.
U.S. Secretary of State, Hillary Clinton, has called the passage of the referendum "inevitable," but said the north may not warm up to the idea of losing oil revenues in the south.
"What happens to the oil revenues? And if you're in the north and all of a sudden, you think a line's going to be drawn and you're going to lose 80 percent of the oil revenues, you're not a very enthusiastic participant," Clinton said in September.
There has been some mistrust between the two sides over the distribution of oil resources, according to the report.
"With both sides hugely reliant on oil revenues from the south, this issue is paramount going into the referendum," said Rosie Sharpe, a Global Witness campaigner. "Suspicions over the sharing of oil revenues under the current peace deal have greatly added to the mistrust between the two parties -- so the single best way to ensure stability after the referendum is to put a transparent and verifiable new oil deal in place."
The report accuses Sudanese officials and the China National Petroleum Corp. of having discrepancies in oil production figures.
"The explanations provided by the Sudanese government and CNPC, the main oil company in Sudan, for why the company's oil production figures were significantly larger than those published by the government, do not stand up to scrutiny," the report said.
The discrepancies mean it's not clear whether officials are implementing the oil agreement fairly, the report said.
The referendum was part of a 2005 peace agreement that ended two decades of violence between the north and the south. The conflict led to the deaths of 2 million people, many from starvation.
Both sides signed the peace agreement, which ended the civil war and gave the south autonomy. The referendum will determine whether Southern Sudan will become an independent state.
If voters approve a split, Southern Sudan will be one of the poorest countries in the world despite its oil wealth. Nine of 10 people in the region live on less than $1 a day.
The region is the size of Texas, but has only 30 miles of paved roads.