But some experts view many settlements as essentially meaningless, particularly since they usually do not require a company to admit to the accusations leveled by the S.E.C. Nearly every settlement allows a company to “neither admit nor deny” the accusations — even when the company has admitted to the same charges in a related case brought by the Justice Department — so that they are less vulnerable to investor lawsuits.

In 2005, Bank of America was one of several companies singled out for allowing professional traders to buy or sell a mutual fund at the previous day’s closing price, when it was clear the next day that the overall market or particular stocks were going to move either up or down sharply, guaranteeing a big short-term gain or avoiding a significant loss.

In its settlement, Bank of America neither admitted nor denied the conduct, but agreed to pay a $125 million fine and to put $250 million into a fund to repay investors. The company also agreed never to violate the major antifraud statutes.

Two years later, in 2007, Bank of America was accused by the S.E.C. of fraud by using its supposedly independent research analysts to bolster its investment banking activities from 1999 to 2001. In the settlement, Bank of America without admitting or denying its guilt, paid a $16 million fine and promised, once again, not to violate the law.

But two years later, in 2009, the S.E.C. again accused Bank of America of defrauding investors, saying that in 2007-8, the bank sold $4.5 billion of highly risky auction-rate securities by promising buyers that they were as safe as money market funds. They weren’t, and this time Bank of America agreed to be “permanently enjoined” from violating the same section of the law it had previously agreed not to break.

In fact, the company had already violated that promise, according to the S.E.C when it was accused last year of rigging bids in the municipal securities market from 1998 through 2002. To settle the charges, Bank of America paid no penalty, but refunded investors $25 million in profits plus $11 million in interest. And, the bank promised again never to violate the same law.

The S.E.C. allowed the bank to settle without admitting or denying the charges, even though Bank of America had simultaneously settled a case with the Justice Department’s antitrust division admitting the very same conduct.