OPEC Secretary General, Nigeria's Mohammad Barkindo, has died unexpectedly at the age of 63, it was announced on Wednesday, leaving the oil cartel without a head at a tumultuous time for the markets.

Barkindo had headed the Organization of the Petroleum Exporting Countries since 2016 and was scheduled to be replaced by Kuwait's Haitham Al-Ghais next month. 

Under his stewardship, the cartel forged ties with 10 other oil-producing countries, such as Russia, to form a wider group known as OPEC+ in a bid to better tame global oil prices, rocked by the challenges of the coronavirus pandemic and more recently the war in Ukraine.  

"We lost our esteemed Dr (Mohammad) Sanusi Barkindo. He died at about 11:00 pm yesterday 5th July 2022," the Nigerian National Petroleum Corporation's chief executive Mele Kyari tweeted, without providing any further details about the circumstances of Barkindo's death.

"Certainly a great loss to his immediate family, the NNPC, our country Nigeria, the OPEC and the global energy community. Burial arrangements will be announced shortly," Kyari wrote.

"This tragedy is a shock to the OPEC Family," Vienna-based OPEC tweeted.

"We express our sorrow and deep gratitude for the over 40 years of selfless service that... Barkindo gave to OPEC. His dedication and leadership will inspire OPEC for many years to come."

Only a few hours earlier, Barkindo -- who had not shown any sign of being ill -- had met Nigerian president Muhammadu Buhari in Abuja, where Buhari praised Barkindo's "distinguished achievements at OPEC. 

- 'Trailblazer' -

"You were able to successfully navigate the organisation through turbulent challenges," Buhari had said.

In a statement, OPEC expressed its "immense sorrow and sadness" at the news, describing Barkindo as "a trailblazer widely admired and respected throughout the globe. A dear friend to many."

Born on April 20, 1959, Barkindo graduated in political science and completed his studies in Oxford and Washington. 

He became Nigeria's representative at OPEC in 1986. Starting from 1992 he occupied a number of positions within NNPC, and took over as the oil major's chief executive in 2009/10. 

The OPEC secretary general does not wield any executive power, but is the cartel's public face and frequently has to act as a diplomat to bring together the different, sometimes conflicting interests of the various member countries.  

For analysts, Barkindo's death will not have an impact on OPEC's strategy in the long-term.

"But in the short-to-medium run, it will increase uncertainty about OPEC's next steps and add to the price volatility as he was a figure of unity for OPEC," said Swissquote analyst, Ipek Ozkardeskaya. 

Spi Asset Management analyst, Stephen Innes, described Barkindo as "a very important figurehead and a stabilising force behind OPEC. 

"But his death is unlikely to change OPEC direction despite more outside politics entering the picture," the expert said, predicting that his successor, Haitham Al-Ghais "augurs for the status quo given Kuwait close ties with Saudi Arabia, which wields the most influence" within the group.