In November last year when Ventures Africa published a story outing Nigerian fashion designer and oil magnate Folorunsho Alakija as the richest black woman in the world, we pegged her net worth at $3.3 billion and explained the rationale for our valuation in detail. See the full story here.

But in our inaugural ranking of Africa’s richest people, which we published on Monday, we place Alakija as the fourth richest person in Africa with a fortune we estimate at $7.3 billion.

Here’s our rationale: In March this year, Petrobas, a Brazilian oil company that owns an 8 percent working interest in OML 127 in which Alakija owns 60 percent, announced that it was actively looking to dispose of its stake for a figure in the region of $1.5 – $2.5 billion. According to sources at Petrobas, there are a number of interested suitors for the stake. The Reuters report is available here.

Since we prefer to be as conservative as possible, we take the low-end and assume that they will fetch $1billion for the stake. If their 8 percent fetches them $1 billion, then Alakija’s 60 percent is worth over $7.3 billion. Alakija also owns a Bombardier Jet as well as a large collection of prime real estate in Nigeria and London.

Alakija was born into a wealthy, polygamous Nigerian family. She started out her professional career in the mid 70s as a secretary at the International Merchant Bank of Nigeria and in the early 80s, she quit her job and went on to study Fashion design in England. She returned to Nigeria shortly afterwards to start Supreme Stitches, a premium Nigerian fashion label that catered exclusively to upscale clientele, including Maryam Babangida, the wife of Nigeria’s former military President Ibrahim Babangida. Leveraging on this proximity to power, she acquired an oil prospecting license – the basis of her enormous fortune today.

The full Rich List is available in the October issue of Ventures Africa magazine. It is also available for download on iTunes store here and on Google play here.