NEW YORK (Bloomberg) — American International Group Inc., which already has suffered more than $60 billion in writedowns and losses, may have to absorb almost $30 billion more because of flaws in the way its holdings are valued.

An examination of AIG's credit-default swaps guaranteeing more than $300 billion of corporate loans, mortgages and other assets not covered by a $152.5 billion federal rescue shows the New York-based insurer may value some of its positions at levels that don't reflect distress in the markets, according to an analyst at Gradient Analytics Inc. and a tax consultant who teaches at Columbia University Business School in New York. Executives at two firms that have similar investments say they account for the securities differently than AIG does.

"Every time I look at their statements I find something new," said Donn Vickrey, executive vice-president of Gradient Analytics in Scottsdale, Arizona. He estimated that AIG may need to take at least $28 billion in additional write-downs on swaps covering European corporate loans and prime residential mortgages, as well as collateralized loan and debt obligations.

"It looks like they haven¿t written down these positions fully yet, and that could be a real problem," said Vickrey, who predicted correctly, as early as February 2008, that the company would have to report increases in its write-downs on its swaps.

Robert Lewis, AIG's chief risk officer, said the company has properly valued all of its swaps and underlying assets and doesn't need to take additional writedowns.