The notional amounts outstanding on derivatives traded on exchanges was $28 tn in March 2008, while the quarterly turnover was $487 tn (we'd need someone who knows the functioning of the futures markets to explain that fully).
So I don't know.
That is actually in the ballpark for the numbers listed in the SiliconValley article. If the credit derivatives number is correct, then the quadrillion dollar plus sounds about right.
