The probe of Libor manipulation is proving to be the tip of the iceberg as inquiries into assets from derivatives to foreign exchange show that if there's a chance to rig benchmark rates in world markets, someone is usually willing to try.

Singapore's monetary authority last week censured 20 banks for attempting to fix interest rate levels in the island state and ordered them to set aside as much as $9.6 billion. Britain's markets regulator is looking into the $4.7 trillion-a-day currency market after Bloomberg News reported that traders have manipulated key rates for more than a decade, citing five dealers.

"It's happened time and again: All of these markets have been influenced by major market-makers, which is a polite way of saying they've been rigged," Charles Geisst, a finance professor at Manhattan College in Riverdale, New York, said in a telephone interview.