Official results of Nigeria's presidential election are expected as early as Monday in what is called a close race between President Muhammadu Buhari and a former vice president, Atiku Abubakar, both from the largely Muslim north. At stake is Africa's largest economy and largest democracy, that is experiencing a demographic boom that could make Nigeria the world's third most populous country by 2050.

The winner inherits an oil-dependent economy still limping back from a recession that began in 2016 after global crude prices crashed. Nearly one-quarter of Nigeria's more than 190 million people are unemployed. Inflation is over 11 percent. The country now leads the world in the number of people in extreme poverty. Frustration with the economy could decide the election, though insecurity is also a major issue.

Here's what to watch in the hours ahead.

Nigerian women vote in Kaduna, Nigeria, Feb. 23, 2019. (AP Photo/Jerome Delay)

WHAT DOES IT TAKE TO WIN?

For the presidency, a candidate must win a majority of overall votes as well as at least 25 percent of the vote in two-thirds of Nigeria's 36 states. If that isn't achieved, the election moves to a runoff.

Top candidates have spent untold millions of dollars campaigning. Buhari is expected to do well in the north and Abubakar in the southeast, while many are watching the southwest anchored by Lagos, Africa's largest city, and the central region where Buhari is criticized over his weak response to deadly farmer-herder clashes.

The results of Saturday's vote have made their way to compilation centers, where election workers hunch over calculators and scribble totals under party agents' watchful eyes. After results are brought in physical form to the capital, Abuja, the electoral commission will announce them state-by-state. Only the commission can announce official results, though local media are broadcasting the tallies of key compilation centers and party supporters tweet purported tallies.

With a surge in candidates — 73 this time, after 14 in 2015 — simply going through results party-by-party could prolong the process.

Some 73 million Nigerians were eligible to vote. The turnout was just below 44 percent in the last election, part of a downward trend.

Nigerians line up to vote at the Narayi primary school in Kaduna, Nigeria, Feb. 23, 2019. (AP Photo/Jerome Delay)

WILL RESULTS BE CONTESTED?

Nigerians were surprised in 2015 when President Goodluck Jonathan conceded before official results were announced to Muhammadu Buhari, a former military dictator who pulled off the first defeat of an incumbent by the opposition in the country's history. This time, Buhari and top challenger Abubakar have been coy about whether they will accept the results, despite signing more than one pledge for a peaceful election.

Between them the two candidates have run for the presidency nine times, with Buhari challenging defeats in court for months at a time, in vain. The president caused an outcry three weeks before this election by suspending the country's chief justice, a key figure in any legal challenge to the vote, over corruption allegations but without the input of other branches of government as required.

Supporters of Nigerian presidential candidate Atiku Abubakar, of the People's Democratic Party, chant slogans during an election campaign rally at the Tafawa Balewa Square, in Lagos, Nigeria, Feb. 12, 2019. (AP Photo/Sunday Alamba)

COULD THE RESULTS CAUSE VIOLENCE?

While more than 800 people were killed after Nigeria's 2011 election, the 2015 vote was one of the country's most peaceful and transparent. Violence was said to be limited to extremist attacks in the northeast.

This time, analysis unit SBM Intelligence reports at least 39 people killed in clashes around the country, including an ambush of soldiers by "political hoodlums" in Rivers state in the turbulent south.

"Enough people have died," the U.S. consul general, John Bray, told reporters on Sunday. In the northern state of Kano, Nigeria's second largest, some have warned of unrest if Abubakar pulls off an upset win.

Nigerian police guard the entrance of the All Progressives Congress (APC) party headquarters where Incumbent President Muhammadu Buhari holds an emergency meeting with senior members of the party in Abuja, Nigeria, Feb. 18, 2019. (AP Photo/Jerome De… — Nigerian police guard the entrance of the All Progressives Congress (APC) party headquarters where Incumbent President Muhammadu Buhari holds an emergency meeting with senior members of the party in Abuja, Nigeria, Feb. 18, 2019. (AP Photo/Jerome Delay)

Supporters of Nigerian presidential candidate Atiku Abubakar, of the People's Democratic Party run after being chased by local security during an election campaign rally at the Ribadu Square in Yola, Nigeria, Feb. 14, 2019. (AP Photo/Sunday Alamba)

With Nigeria's top political parties said to be driven more by access to power than issues, competition for hugely lucrative posts can turn ugly at any level — and the country also awaits the results of more than 450 National Assembly seats.

"The risk of violence is quite higher in this election," and not because of religion or ethnicity, said Idayat Hassan, director of the Center for Democracy and Development. "It has to do more with ... how much these people really want to win at all costs."