North and south Sudan have accepted a ruling by judges in The Hague which gives the north control of an oilfield.
The Permanent Court of Arbitration redrew the boundaries of Abyei region, which became a flashpoint during a 22-year-long war between north and south.
They reduced the size of the region, putting the Heglig oilfield outside of Abyei - where most of the population is said to be loyal to the south.
The north declared the ruling a victory while the south said it was satisfied.
The court was ruling only on where Abyei's borders should lie - not on who owns the land.
But analysts say the ruling is crucial in determining the ownership of the oilfields.
Abyei's inhabitants will be asked in a referendum in 2011 whether they want to be a part of north or south Sudan - and analysts say they are likely to opt for the south.
The Hague panel reduced the size of Abyei compared with proposals laid out after the 2005 deal which brought and end to the long-running civil war.
The decision effectively awards more land and mineral wealth to the north.
The BBC's James Copnall in the capital, Khartoum, says the reaction on the ground to the judges' ruling will be a key test of the peace between north and south.
'Victory for peace'
Dirdeiry Mohamed Ahmed, the head of the northern government delegation at The Hague, called the decision a victory.
"We welcome the fact that the oilfields are now excluded from the Abyei area, particularly the Heglig oil field," the Associated Press quoted him as saying.
The south's delegate Riak Machar, vice president in southern Sudan's semi-autonomous government, described the decision as "balanced" and said he was committed to respecting it.
"I think this is going to consolidate peace in Sudan. It is a victory for the Sudanese people and a victory for peace," he said.
The issue was referred to The Hague last year after clashes broke out in Abyei town, killing about 100 people and forcing tens of thousands to flee.
UN peacekeepers beefed up their presence in Abyei this week amid fears that a controversial ruling could spark violence.
Douglas Johnson, who was part of the international panel who drew up the 2005 border proposals, said The Hague agreement had respected ethnic boundaries as well as north and south rivalries.
"Each side can say they were right about something, and each side can come away feeling that they have been given something from this arrangement," he told the BBC World Service.
The area is home to Arab cattle herders known as the Misseriya who are loyal to the north, and the Dinka Ngok, part of the largest ethnic group of the south.
The UN increased its presence in Abyei this week
Both sides compete for resources like land for grazing and water - rivalries that were exploited during the civil war with both sides being used as proxy armies.
The conflict between the mainly Muslim north and the Christian and animist south claimed 1.5 million lives.
Pierre-Marie Dupuy, head of The Hague panel, moved to counter concerns that the new border could rob any group of access to vital resources, saying the rights of the nomadic tribes living in the region would be protected.
"Boundaries are not barriers," he said.
UN special envoy to Sudan Ashraf Qazi said the Abyei border ruling would pave the way for the 2005 peace deal to be implemented as a whole.
"The rights of both communities have been guaranteed as a matter of international law," he said.
"So even if anybody is not 100% satisfied, I do believe this has been a win-win decision for both sides."
As part of the peace agreement the south will hold a referendum in 2011 on whether to become independent from the north.