Mother-of-four, Folorunsho Alakija, 62, started her career as a secretary in a bank then studied fashion and launched a label but her big break was oil.

In 1993, her company, Famfa Oil, was awarded an oil prospecting license, which later became OML 127, one of Nigeria's most prolific oil blocks.

The company owns a 60 per cent stake in the block, valued at around $7.3 billion, Ventures Africa reports.

According to Forbes, Oprah Winfrey is worth $2.9 billion.

Move over Oprah, Nigerian oil tycoon Folorunsho Alakija is now the richest black woman in the world with an estimated fortune of $7.3 billion.

Africa boasts 55 billionaires - far more than previously thought - and they're worth a staggering $143.88 billion in total, according to pan-African magazine Ventures Africa.

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