FACTBOX: Southern Sudan's independence referendum

(Reuters) - Sudan's oil-producing south has been promised a referendum in a year's time on whether to separate and become an independent country or remain united with the north.

Following are some key facts about the vote.

BACKGROUND

The vote was promised in the 2005 Comprehensive Peace Agreement that ended more than two decades of civil war between north and south Sudan.#

The vote will take place on January 9, 2011, according to a long-delayed referendum bill passed by Sudan's parliament late last month. Southerners will either "confirm the unity of the Sudan" or "vote for secession."

There will be a simultaneous vote on whether the contested central oil region of Abyei should join the south.

LIKELY OUTCOME

Southern rebel leader John Garang promised to fight for a "New Sudan" -- a vision of a unified country, with equality between its races and regions. But that utopian plan faded after his death in a helicopter crash in July 2005.

The current leadership of Garang's Sudan People's Liberation Movement (SPLM) have been making increasingly separatist statements, despite the official line that they are campaigning to make unity attractive.

Support for secession is thought to be overwhelming among a population embittered by decades of civil war, underdevelopment and perceived exploitation by the northern Muslim elite.

THE DETAIL

Voters have to show they either have ethnic links to "the indigenous groups resident in southern Sudan" before January 1 1956, or that their family has lived in the south "continuously without interruption" since that date. They also have to be registered, sane and at least 18 years old.

At least 60 percent of registered voters have to take part for the referendum to be valid. If that target is not met, the vote will be held again within 60 days. More than half of the electorate would have to choose independence for the south to secede or choose unity to remain as one country.

OUTSTANDING ISSUES

Sudan now has just 12 months to resolve a long list of outstanding issues.

The first item is to set up an independent "Southern Sudan Referendum Commission" to work out the whole process.

Both sides also have to prepare for a possible vote for secession and reach agreements on a range of areas on everything from currency to the sharing of oil wealth, national assets and debt. The south, where most follow Christianity and traditional beliefs, needs to decide what it would call itself.

Perhaps most pressingly, north and south Sudan have still not agreed the position of their shared border, along which most of Sudan's oil fields lie.

RISKS

Presidential advisor Ghazi Salaheddin, from the NCP, warned there was a risk of war if outstanding issues on the border, nationality, debt and other areas were not resolved ahead of the referendum.

Analysts have warned conflict may also arise if the north refuses to accept an independence vote and the resulting loss of control over oilfields.

The International Crisis Group warned an independent south Sudan could become a failed state "overwhelmed by internal divisions, poor governance and bureaucratic deficiencies."

(Writing by Andrew Heavens; Editing by Giles Elgood)