More than 2,000 people have died in ethnic clashes in Sudan this year
South Sudan says it has achieved a breakthrough in talks with the north over terms for a referendum on full independence for the south.
South Sudan's Vice-President Riek Machar said the vote in 2011 will require a simple majority as long as two-thirds of voters takes part.
In the past, central government in the north has insisted that 75% of voters must agree to independence.
The issue was one of a number that have caused tension between north and south.
Diplomats have been warning of a possible resumption of the 22-year civil war.
Mr Machar announced the deal in the South Sudan capital Juba following talks in Khartoum with national Vice-President Ali Osman Taha.
"We have overcome the differences over the outstanding issues, and there is an agreement," Mr Machar said.
He said he welcomed the agreement, although the south had pushed for a lower turnout requirement.
"I would have wished the turnout quorum to be a little bit lower, not that the south cannot meet the two-thirds registered voters... but because of the difficulties we have such as security, transport, logistics, movement of people," he said.
Mr Machar said that all southerners will be allowed to vote, including those in the northern capital Khartoum and those outside Sudan.
The BBC's Peter Martell in Juba says that although the agreement still needs to be ratified by officials in the north and south, it marks a breakthrough.
There was no immediate comment from the President Omar al-Bashir's National Congress Party.
However, our correspondent says many in the south are already celebrating what they see as an important step towards the referendum.
The vote, due in January 2011, is part of a 2005 peace deal that ended the civil war.
The conflict pitted the Muslim north against Christians and animists in the south, leaving some 1.5m people dead.
At least 2,000 people have been killed in bitter ethnic clashes in South Sudan, notably Jonglei state, this year.
Mr Machar's SPLM party has accused the northerners of trying to stir up unrest ahead of the referendum and national elections due in 2010.