"Move over, Oprah!" Ventures Africa says in its latest edition published this week.
Editor-in-chief Uzodinma Iweala said Tuesday their estimates are "on the conservative side."
The report predictably identifies Nigerian manufacturer Aliko Dangote as the richest African worth $20.2 billion, among 20 Nigerians listed.
It surprises by identifying oil tycoon Folorunsho Alakija as the richest black woman in the world, worth $7.3 billion.
Forbes magazine in its respected list had estimated Alakija's fortune at $600 million and Oprah Winfrey's worth at $2.9 billion. Iweala said his researchers are "closer to the ground" and expect to unearth moreAfrican billionaires.