Flaws in the way Libor is set allowed individual banks to manipulate the key global interest rate for profit for years, according to traders.

While employees allegedly tried to rig the benchmark for $500 trillion of securities worldwide, they didn't need to conspire with counterparts at other firms to affect where the rate was set each day, as some regulators concluded, said the people, one of whom lost his job for trying to distort the rate. By nudging their own firms' submissions up or down in small increments they could boost the value of their trading books or cut their losses, said the people, who asked not to be identified because regulators are still investigating the Libor-setting process.

The ability of a single bank to rig the London interbank offered rate also is highlighted by e-mails disclosed when Barclays Plc paid a 290 million-pound ($452 million) fine to U.S. and U.K. regulators for manipulating the benchmark, and by academic studies. The settlement forced the resignations of the top three executives at Britain's second-biggest bank by assets, including Chief Executive Officer Robert Diamond, 60.