Former OPEC secretary general Dr. Alhaji Rilwanu Lukman, who led the oil producer group between 1995 and 2000, passed away in the early hours of Monday in Vienna, the organization said in a statement. He was 75.
Nigeria-born Lukman's career in the oil industry spanned five decades, during which time he served as the country's oil minister before leading the Organization of the Petroleum Exporting Countries (OPEC) as secretary general and president.
He was Nigeria's oil minister between 1986 and 1990 and returned to the role for two years in 2008.
After retiring from OPEC Lukman settled in Vienna, working as a consultant for international oil companies and traders.
The cause of his death Lukman's not immediately clear. Oil industry sources said he was thought to have battled illness for a long time.
Reporting by David Sheppard