Fighters with the Movement for the Emancipation of the Niger Delta (MEND) raise their riffles to celebrate news of a successful operation by their colleagues against the Nigerian army in the Niger Delta on September 17, 2008. PIUS UTOMI EKPEI | AFP | Getty Images

Nigeria's President Muhammadu Buhari has won a second term in office after a contentious Nigerian election this weekend, but the opposition are refusing to accept the outcome and a period of uncertainty and unrest could follow. That could impact the OPEC member's oil production, according to RBC Capital Markets' Global Head of Commodity Strategy Helima Croft. "With the opposition alleging fraud and refusing to the accept the outcome, the risk of further unrest remains high in the weeks ahead, especially in the restive oil region, which was the scene of some of the worst Election Day unrest," Croft said in a note Wednesday co-authored with RBC analysts Christopher Louney, Michael Tran and strategist Megan Schippmann. "If this election does bring a return to militancy in Nigeria's oil region and major infrastructure attacks, it would be a very material event for the oil market, with two OPEC countries (Venezuela and Iran) under U.S. sanctions and Saudi Arabia continuing to cut production," they noted. "Given the premium that the American president places on low oil prices, he will need to hope that Nigeria does not revert to past practice." Nigeria's election last weekend did not run smoothly and was marred by delays, logistical problems, outbreaks of violence and deaths, and allegations of vote rigging. Buhari, who leads the All Progressives Congress (APC), won the election with almost 15.2 million votes (or 57 percent), the country's Independent National Electoral Commission (INEC) announced Tuesday evening. Buhari's nearest rival, Atiku Abubakar, who heads the People's Democratic Party (PDP), received around 11.2 million votes, or 42 percent.

Supporters of the ruling All Progressives Congress (APC) celebrate with party flags in Abuja, Nigeria, after candidate President Mohammadu Buhari was re-elected on February 26, 2019. KOLA SULAIMON | AFP | Getty Images

INEC, which made the decision to postpone the election for a week due to operation and logistical challenges, said that it had been made aware of irregularities prior to the election — although it has itself been the target of accusations from both the main parties, accusing it of trying to influence the result in favor of the other. Tweet:

Niger Delta unrest

Nigeria is a significant oil and gas producer — the largest in Africa — and has the highest output among OPEC's African members, producing almost 1.8 million barrels a day (mb/d) in January, according to the latest data from OPEC. Nigeria is seen as one of the "fragile five" members of OPEC, however (along with Iran, Iraq, Libya and Venezuela) because its oil-rich Niger Delta region in the south of the country has been plagued with long-running unrest and disruption to, and sabotage of, its oil production from militant groups. There are a handful of militant groups operating in the region, including the Niger Delta Avengers, Niger Delta People's Volunteer Force and the "Movement for the Emancipation of the Niger Delta," or MEND. They say that their region's oil wealth and environment is being exploited by foreign oil companies and the Nigerian government.

Fighters with the Movement for the Emancipation of Niger Delta (MEND) prepare for an operation against the Nigerian army in Niger Delta on September 17, 2008. PIUS UTOMI EKPEI | AFP | Getty Images

What's more, the Niger Delta region is a stronghold for the opposition PDP and violence in the region ahead of the election was pronounced with several deaths, including that of one of the electoral commission's staff who was reportedly shot on election day. Any disruption to its oil sector could have an impact on wider oil markets and price volatility, especially with output lower from Venezuela and Iran. President Donald Trump has repeatedly criticized OPEC and its allies for oil price rises. Benchmark Brent crude futures were trading at $65.58 per barrel Wednesday while West Texas Intermediate (WTI) futures stood at $55.92.

High risk of 'further bloodshed'