The most expensive mistake on this list is the 1988 Piper Alpha disaster, with insured losses of £1.7bn, followed by the 2003 Cedar Fire at roughly $1.3 billion. Ten costly human errors are ranked here by their approximate cost in dollars, from a North Sea oil platform to a trader’s keyboard. Some figures are insured losses, some are sale prices, and a few are our own labelled estimates.
| # | Mistake | Year | Approximate cost |
|---|---|---|---|
| 1 | Piper Alpha maintenance handover | 1988 | About £1.7 billion insured loss |
| 2 | Cedar Fire started by a lost hunter | 2003 | About $1.3 billion in damage |
| 3 | Three Mile Island reactor accident | 1979 | About $1 billion cleanup |
| 4 | Thrown-away bitcoin hard drive | 2013 | 8,000 bitcoin, worth hundreds of millions at 2025 prices |
| 5 | Daimler and Chrysler | 1998 to 2007 | Daimler paid $650 million to offload Chrysler |
| 6 | Ariane 5 software bug | 1996 | More than $370 million |
| 7 | Mizuho Securities typo | 2005 | At least 27 billion yen (about $225 million) |
| 8 | French trains too wide for platforms | 2014 | About 50 million euros |
| 9 | Titanic | 1912 | About $7.5 million to build, plus about 1,500 lives |
| 10 | Selling Alaska | 1867 | $7.2 million sale price |
1. The Piper Alpha handover: about £1.7 billion
On the night of 6 to 7 July 1988 the Piper Alpha platform in the North Sea exploded and burned, killing 165 men on board and two rescuers. At the time it produced roughly a tenth of North Sea oil and gas. The total insured loss came to roughly 1.7 billion pounds, which makes it one of the costliest man-made disasters on record.
The chain began with paperwork. A condensate pump was under maintenance and its safety valve had been removed, but the permit saying so was misplaced when the night shift took over. Nobody on the new shift knew, and they tried to start the pump. Better handovers and the safety regime that followed changed offshore work for good.
We ranked it first on the size of the insured loss, converted loosely into dollars.
2. The lost hunter and the Cedar Fire: about $1.3 billion
In October 2003 a novice hunter named Sergio Martinez got disoriented in the back country of San Diego County and fired a shot to attract attention. The resulting Cedar Fire burned 273,246 acres, destroyed 2,820 buildings including 2,232 homes, and killed 15 people.
Damage came to just over $1.3 billion. Martinez was sentenced in 2005 to six months in a work-furlough program, 960 hours of community service, five years of probation and $9,000 in restitution. That works out to well under a thousandth of one percent of the bill.
Our cost figure is the damage total from the state fire agency, not an insurance estimate.
3. Three Mile Island: about $1 billion
At 4:00 a.m. on March 28, 1979, a stuck-open relief valve let cooling water drain from the Unit 2 reactor in Pennsylvania. Operators misread the situation, and a confusing control room did not help. The core partly melted down. It is still the worst accident in U.S. commercial nuclear power history, though the radioactive release was small.
Cleanup ran from August 1979 to December 1993 and cost about $1 billion at the time, roughly $2 billion in 2025 dollars. The accident slowed new reactor construction in the U.S. for years. The sister reactor, Unit 1, is expected back in service around 2027 or 2028 to supply power for Microsoft data centers.
We used the cleanup cost as the headline number and left out lost electricity sales, which no one has tallied cleanly.
4. The hard drive in the landfill: 8,000 bitcoin
In 2013 James Howells of Newport, Wales, reportedly threw away a hard drive that held the keys to 8,000 bitcoin he had mined years earlier. Most reports now say 8,000, not the 7,500 once quoted. At 2025 prices, press coverage valued the coins somewhere between about $780 million and $923 million, depending on the day.
Howells spent years trying to get permission to dig through the landfill. A court rejected his claim in January 2025, and in August 2025 he said he was no longer pursuing a purchase of the site. Coverage in 2026 describes the physical search as over.
The valuation is our rough range, since the dollar figure moves every time bitcoin does. The 2013 value in that period was a small fraction of today’s.
If you like stories of money lost the hard way, read 15 Times People Lost Fortunes in Crypto.
5. Daimler and Chrysler: $650 million to walk away
Daimler-Benz and Chrysler merged in 1998 under the name DaimlerChrysler, in a deal that was billed at the time as a merger of equals. Nine years later, in May 2007, the company agreed to sell 80.1% of Chrysler to Cerberus Capital Management.
The sale price was reported as $7.4 billion, but the terms saw Daimler pay Cerberus $650 million to take Chrysler and its liabilities off its hands. Daimler kept a 19.9% stake. Older retellings cite a $13 billion loss that we could not confirm, so we used the verified $650 million cash cost instead.
The real loss was probably far larger, because nine years of capital and management attention are not on the ledger.
6. The Ariane 5 software bug: more than $370 million
The maiden flight of Europe’s Ariane 5 rocket lifted off on 4 June 1996 carrying four research satellites. About 37 seconds later it veered off course and destroyed itself.
The culprit was code reused from the older Ariane 4. A number that was too large for the space reserved for it triggered an error, which shut down the navigation computers on a rocket that could not fly without them. The programmers had protected only four of seven critical variables against that overflow.
Losses came to more than $370 million. The inquiry board said the cause was a design error, not a random failure, which made it one of the best-known software bugs ever.
7. The Mizuho typo: about $225 million
On December 8, 2005, a trader at Mizuho Securities was supposed to sell 1 share of J-Com at 610,000 yen. The order went in as 610,000 shares at 1 yen, on the stock’s first day of trading on the Tokyo exchange. The firm tried to cancel, but the system did not allow it.
Mizuho’s president said the loss would be at least 27 billion yen, about $224 million, and it could grow as the firm bought shares back. The Nikkei fell nearly 2% that day.
We took the company’s own 27 billion yen figure as the base.
8. The French trains that did not fit: about 50 million euros
In 2014 France’s rail operator and its network owner admitted that new regional trains were a few centimeters too wide for many station platforms. The trains were part of a huge order of around 2,000 regional trains, and 341 of them were affected by the width problem.
Roughly 1,300 platforms had to be trimmed back. The fix was priced at 50 million euros, or about $68 million at the time. The error came from a miscommunication between the two organizations over platform dimensions based on old stations.
We kept the reported 50 million euro repair bill as the cost of the mistake.
9. The Titanic: about $7.5 million to build, and about 1,500 lives
RMS Titanic hit an iceberg on her maiden voyage and sank in the early hours of 15 April 1912. Of the 2,208 people aboard, approximately 1,500 died, which makes it one of the deadliest peacetime sinkings of a single ship. Modern researchers put the toll at 1,496.
The build cost of $7.5 million is in 1912 dollars, and we did not convert it to today’s money because we could not verify a rate. By cost alone, the sinking sits low on this list. By consequence, it does not.
10. Selling Alaska: $7.2 million
Russia sold Alaska to the United States in 1867 for $7.2 million, which is about $132 million in 2024 dollars. The Senate ratified the treaty on April 9 of that year, and American sovereignty took effect in October.
The sale looks cheap in hindsight. The Prudhoe Bay field, discovered long after the sale, originally contained about 25 billion barrels of oil. Popular retellings put Alaska’s oil and gas at over $200 billion today, but we could not verify that, so we leave the price off.
Russia was short on cash and worried it could not defend the territory, so calling the sale a blunder is easier now than it was then.
Watch on Alux
Keep reading
- 5 cheap mistakes the rich avoid: the small-scale version of costly errors
- 15 times people lost fortunes in crypto: more stories of money lost for good
- 15 cheap mistakes the rich never make: what to avoid in your own money
The habits that let people afford this
Short audio lessons on money, mindset and discipline, in the Alux app.
Get the Alux app →FAQ
What is the most expensive mistake in history?
On our list it is the 1988 Piper Alpha disaster, with insured losses of about £1.7 billion. Other mistakes, such as selling Alaska, may have cost more in lost value but cannot be priced precisely.
What was the costliest software mistake?
The Ariane 5 rocket failure in 1996 cost more than $370 million. A number too large for its storage space shut down the navigation computers 37 seconds after liftoff.
How did a typo cost Mizuho Securities $225 million?
A trader entered an order to sell 610,000 shares of J-Com at 1 yen each instead of 1 share at 610,000 yen. Mizuho’s president said the loss would be at least 27 billion yen.
Did James Howells ever recover his bitcoin?
No. He reportedly threw away a hard drive holding 8,000 bitcoin in 2013. A court rejected his claim in January 2025, and he said in August 2025 he was no longer pursuing a purchase of the landfill.
How much did the Three Mile Island cleanup cost?
About $1 billion, between 1979 and 1993. That is roughly $2 billion in 2025 dollars.
Why is Titanic not higher on the list?
Her build cost was only about $7.5 million. Titanic is remembered for its roughly 1,500 deaths rather than the money lost.
How we put this list together
We ranked each mistake by the best verified cost we could find, converting loosely into dollars, and labelled estimates where no reliable total exists. Figures we could not verify were corrected or dropped.
Last updated: October 2026.
