EU antitrust regulators on Thursday fined Barclays, Credit Suisse, HSBC, and NatWest €344 million ($390 million) for foreign exchange market rigging, closing a key chapter in a high-profile investigation.

       UBS avoided a €94 million fine by alerting the European Commission to the cartel, which was set up via a chatroom known as “Sterling Lads”.

       HSBC received the largest fine at €174.3 million, followed by Credit Suisse at €83.3 million, Barclays at €54.3 million and RBS at €32.5 million. Barclays, HSBC and RBS —known as NatWest since a rebranding — admitted wrongdoing in return for a reduced penalty.

       NatWest said the misconduct took place about a decade ago in a single chatroom, involved a former employee and that its culture and controls had since fundamentally changed. UBS said it had been the first bank to disclose potential misconduct and was pleased the matter was resolved. Barclays, Credit Suisse and HSBC declined to comment.

       Some of the world's biggest banks have been fined more than $11 billion collectively by US and European regulators since allegations first surfaced around 2013 that dealers were rigging the world's largest financial market. Dozens of traders were suspended or fired.

       The latest investigation focused on foreign exchange (forex) spot trading of G10 currencies, the most liquid and traded currencies in the world, which include the dollar, pound and euro. Traders exchanged sensitive information and trading plans and sometimes coordinated strategies through the online chatroom, the Commission said.

       The EU has already sanctioned some of the same banks over similar conduct in 2019 in a settlement featuring chatrooms called “Three Way Banana Split”, “Only Marge”, “Essex Express”, and “Semi Grumpy Old Men”.