Barclays Plc investors, blindsided by the bank's $451.4 million regulatory fine for trying to rig benchmark rates, saw the stock drop 16 percent a day later. Other bank shareholders may be just as surprised.

Barclays, like other lenders that help set key rates for $360 trillion in securities, has given investors scant guidance on the liability they face for alleged market manipulation. More than a dozen banks are being probed by U.S., Asian and European regulators for collusion in setting interbank lending rates. The others have mirrored Barclays on minimal disclosure.

“The automatic reaction from investors is: 'Who's next?'” said Todd Hagerman, a New York-based analyst at Sterne Agee & Leach Inc. who recommends investors remain “cautious” on the biggest U.S. banks. “It's fair to assume that legal and related professional fees and associated reserves are going to continue to remain elevated, if not increase.”