Five of America's largest banks, most of which have received $145 billion in taxpayer bailout dollars, still face potentially catastrophic losses from exotic investments if economic conditions substantially worsen, their latest financial reports show. Citibank, Bank of America, HSBC Bank USA, Wells Fargo Bank and J.P. Morgan Chase reported that their current" net loss risks from derivatives - insurance-like bets tied to a loan or other underlying asset - surged to $587 billion as of Dec. 31 ... a jump of 49 percent in just 90 days. The banks' potentially huge losses ... shed new light on the hurdles that President Barack Obama's economic team must overcome to save institutions it deems too big to fail. While the potential loss totals include risks reported by Wachovia Bank, which Wells Fargo agreed to acquire in October, they don't reflect another Pandora's Box: the impact of Bank of America's Jan. 1 acquisition of tottering investment bank Merrill Lynch, a major derivatives dealer. The risks of these off-balance sheet investments, once thought minimal, have risen sharply. Fears are rising that a spate of corporate bankruptcies could deliver a new, crippling blow to major banks. Because of the trading in derivatives, corporate bankruptcies could cause a chain reaction that deprives the banks of hundreds of billions of dollars in insurance they bought on risky debt or forces them to shell out huge sums to cover debt they guaranteed. The biggest concerns are the banks' holdings of contracts known as credit-default swaps.