Besides ranking him as sixth richest person in the world with a net worth of 42 billion dollars, Forbes had credited him for having added maximum wealth in its last annual rankings in March.

Since then, his net worth has declined to 12 billion dollars, the magazine said in a news report titled "Billionaire Blowups of 2008".

"The biggest loser of all was Anil Ambani. Touted on the cover of our 2008 billionaires issue for having added 24 billion dollars to his fortune in one year, Ambani has dropped 30 billion dollars since then," the report said.

The report further added that three of "his fellow countrymen--estranged brother Mukesh, steel tycoon Lakshmi Mittal and Indian K P Singh, all of whom ranked earlier among the world's 10 richest--lost more than 20 billion dollar apiece."

Noting that 2008 was "a dreadful year for the world's wealthiest as markets and currencies around the world tumbled," Forbes said that over 300 of the 1,125 billionaires have lost at least one billion dollars since March.

While several dozen have lost more than five billion dollars, the 10 richest from annual 2008 rankings have lost about 150 billion dollars.

This is primarily driven by steel tycoon Lakshmi Mittal, estranged brothers Mukesh and Anil Ambani and property baron K P Singh together losing 100 billion dollars.

The publication has also listed out its top "10 Billionaire Blowups," noting that "even in such an awful year, the stories of a few billionaires and now former billionaires stand out as particularly dreadful."

"The biggest billionaire gainer last March is now the year's biggest loser. Ambani lost 30 billion dollars in the past nine months, more than anyone in the world. Stock of his telecom company dropped after his estranged brother helped scuttle a deal with African telecom MTN."

Forbes, however, noted that with 12 billion dollars worth of fortune, Anil Ambani "remains quite wealthy... That is something many others can't claim".

The list of 10 billionaire blowups includes two more Indians -- wind power major Suzlon's chief Tulsi Tanti and online gambling firm PartyGaming's founder Anurag Dikshit.

"Dozens of the world's wealthiest lost billions in recent months, yet these 10 distinguish themselves for some of the biggest flops. But they lost more than money. Some lost board seats. Several faced margin calls. A couple got in trouble with the law. All suffered hits to their reputations."

Tulsi Tanti's wealth dropped by 2.5 billion dollars to stand at 500 million dollars, while Dikshit's current net worth is about one billion dollars, down from 1.6 billion dollars in March 2008.