The encyclopedia · Trading & Investing · Operational decision · 2008
A junior trader hid €50B of bets and cost Société Générale €4.9 billion
Jérôme Kerviel built unauthorized positions worth more than his bank, hiding them with fake trades. Unwinding them in a falling market cost €4.9 billion.
Société Générale · 2008-01
What happened
Jérôme Kerviel was a junior trader at Société Générale, one of France's largest banks, working in the 'delta one' desk that handles program trading and index futures. He had come up through the bank's middle and back office, so he knew its control systems intimately. Beginning in 2006 and accelerating through 2007, Kerviel built up enormous unauthorized bets on European stock-index futures — at one point totaling as much as €49.9 billion, more than the bank's entire market value.
To conceal the positions, Kerviel created offsetting fictitious trades and used his knowledge of the bank's systems to dodge detection — when a fake trade was questioned, he would cancel it and replace it with another using a different instrument. The bank says it uncovered the unauthorized trading on January 19, 2008. Over the following three days, beginning January 21, Société Générale frantically closed out Kerviel's positions — just as global equity markets were plunging.
Unwinding such huge positions into a falling market locked in a loss of about €4.9 billion (roughly $7 billion), one of the largest trading losses in banking history. Kerviel was convicted of breach of trust, forgery and unauthorized use of the bank's computers, and sentenced to prison. The case echoed Barings Bank a decade earlier, and raised an uncomfortable question that skeptics still ask: how could unauthorized trading on such a scale go unnoticed inside a major bank?
Why it happened
- Kerviel's back-office background let him understand and evade the bank's control systems, hiding positions with fictitious offsetting trades.
- The same environment that generated the trades also booked and monitored them, so there was no effective independent check.
- Enormous positions (up to €49.9B) went undetected, partly because they were buried in the high volume of low-risk trades normal for the desk.
- The bank's decision to unwind the positions during a market crash turned hidden risk into a realized multi-billion-euro loss.
The lesson
The trader who reports his own profits is grading his homework. Kerviel hid €50B because one desk made, booked and checked the trades. Segregate duties — and investigate profits that look too good.
Aftermath
Société Générale survived the loss but the scandal became, with Barings, the defining case of rogue-trading risk and the failure of internal controls. Kerviel was convicted and imprisoned, and the bank was itself fined by regulators for weak controls. The episode is taught as a warning that controls must be independent of the people they monitor, that spectacular 'profits' deserve scrutiny rather than praise, and that the ability to hide a position is itself the failure — long before the market turns it into a loss.
Sources
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