The Sudanese Government and southern rebels have signed an agreement to share the country's wealth.
Both sides have come under intense pressure to end the war
It sets out how they will share the revenues, mostly from oil, after the 20-year civil war between Muslim north and Christian and animist south.
But the two sides still have to agree on the administration of three disputed areas and how to share out government and civil service jobs.
Norwegian mediators say a final deal to end the war could be signed within weeks.
"The Sudan peace process is now truly irreversible," said rebel leader John Garang.
"This moment, in which we have signed an agreement on wealth sharing, spells the end of a long episode of war and conflict in our country," said vice-president Ali Osman Taha.
Lasted 20 years
Muslim north vs Christian and animist south
Status of 3 central states
Sharing out jobs
Delegates ululated and cheered as the deal was signed by the two men in the Kenyan town of Naivasha.
BBC East Africa correspondent Christian Fraser says one of the biggest obstacles in the way of a final agreement has been removed.
Both sides have been under intense pressure, not least from the United States, to end the war which has killed some two million people.
Last year US Secretary of State Colin Powell attended the talks and said that a final agreement to end the war would be signed before the end of 2003.
After months of talks and years of bitter fighting over the country's oil resources, the central government and the rebel SPLA have agreed to divide the country's oil wealth equally.
They will also set up a presidential commission to oversee future exploration and the fair division of oil revenues.
During a six-year transitional period, which will begin when a comprehensive agreement is signed, the south will have an autonomous administration.
There will be Islamic Sharia banking in the north, Western banking in the south and a new national currency.
Under Sharia law, banks are not allowed to charge interest.
Mr Garang and Mr Taha will return to their negotiations on the two outstanding issues after signing the agreement on wealth.
The SPLA says the three central states of Abyei, Blue Nile State and the Nuba mountains should be considered part of the south, while the government disagrees.
The two sides have also to decide on whether the capital, Khartoum should be governed by Islamic Sharia law and how many ministerial and civil service jobs should be given to the rebels.