President Muhammadu Buhari will hold Nigeria’s oil portfolio in his new Cabinet, rather than trust anyone else with the source of most of Nigeria’s revenue, he told Reuters on Tuesday.

Buhari, who took office at the end of May promising to combat corruption, has made clear he wants to overhaul the oil sector in Africa’s biggest economy, which provides the government with around 70 percent of its revenue.

“I intend to remain the minister of petroleum resources,” Buhari said in an interview on the sidelines of the annual meeting of world leaders at the United Nations General Assembly in New York.

A minister of state will oversee the day-to-day issues of the petroleum sector, he said.

Buhari has not named a Cabinet but is expected to submit candidates to parliament in the coming days.

A former general who briefly ruled Nigeria 30 years ago, Buhari has deep knowledge of the oil sector, having been head of the Petroleum Trust Fund under military ruler Sani Abacha in the 1990s and oil minister in the 1970s under President Olusegun Obasanjo.

A collapse of global oil prices has whacked Nigeria’s public finances and weakened its naira currency, delaying public salaries and fueling inflation.

Buhari has said he will trace and recover what he has called “mind-boggling” sums of money stolen over the years from the oil sector.

The dealings inside the state-owned company NNPC are so opaque that PriceWaterhouseCoopers, commissioned to conduct a forensic audit over the missing funds, said it was unable to obtain sufficient account documentation.

Not only is oil money stolen through accounting gymnastics and oversight gaps, but oil itself goes missing at unmetered oilfield wellheads, pipeline taps and export terminals.

Buhari has already split the NNPC into two entities, and said on Tuesday he was considering breaking up the company further to improve efficiency and better root out corruption.

“I haven’t absolutely made up my mind about that. We want to see what we have done in reducing the size and redeploying most of the management. We want to see the impact of that before we decide further.”

He said he would re-evaluate the issue in about 18 months.

Reuters