Ambani, who owns 44.7 percent of Reliance Industries Ltd. (RIL), Operator of the world's biggest oil refining complex and owner of India's biggest natural gas field, ranks 11th among the world's richest. The 54-year-old industrialist's stake in the Mumbai-based energy explorer and refiner is worth $24 billion.

Last year's 35 percent drop in Reliance's share price prompted Ambani to offer to buy back the stock for the first time in seven years.

Reliance's cash more than tripled in the past two years to $15 billion after BP Plc (BP/), Europe's second-largest oil company, bought stakes in 21 fields in India for $7.2 billion last year.

Two years ago, India's richest man completed his 27-story house in Mumbai, where half of the city's population lives in slums. The skyscraper, called Antilia, is worth at least $500 million, according to Anuj Puri, chairman and country head of Jones Lang LaSalle.