European regulators have fined eight large banks a total of more than $2 billion over an illegal cartel scheme to fix interest rates. The fine, the largest ever issued in such a case by the European Union, comes after a two-year investigation into banks' collusion. And the inquiry isn't yet complete.

Two American banks — JPMorgan Chase and Citigroup — are included in the list of financial institutions fined as part of a settlement deal. Several banks that cooperated with investigators saw their fines reduced or eliminated.

"Barclays received full immunity for revealing the existence of the cartel and thereby avoided a fine of around 690 million euros [$938 million] for its participation in the infringement," according to a news release from the EU.

Similarly, UBS also received immunity from what would have been a fine of around 2.5 billion euros — about $3.4 billion — in return for its cooperation.

For NPR's Newscast unit, Teri Schultz reports from Brussels:

"EU regulators found traders at some of the world's largest banks joined forces to manipulate borrowing rates, the euro interbank offered rate, or Euribor, and London interbank offered rate, or Libor. A record fine of about $2.3 billion dollars will be shared among eight institutions including Citigroup, Deutsche Bank and Royal Bank of Scotland.

"EU competition commissioner Joaquin Almunia says if the public could hear the conversations between traders found to be manipulating benchmark interest rates they would be 'appalled.'

" 'They discussed confidential, commercial and sensitive information that they are not allowed to share with other market players according to the antitrust rules,' Almunia says.

"Almunia says today's fines are not the 'end of the story,' as regulators continue their investigations."

The two remaining banks are Société Générale and RP Martin.

The collusion centered on interest rate derivatives denominated in two currencies: the euro and the Japanese yen. The overall fine of more than 1.71 billion euros reflects a reduction of 10 percent that was given to the institutions for agreeing to settle the case.

The New York Timeshas this explanation of how Libor and Euribor rates are set: "Banks submit the rates at which they would be prepared to lend money to each other, on an unsecured basis, in various currencies and varying maturities. Those rates are averaged, after the highest and lowest ones are eliminated, and that becomes that day's rate."

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