The day before Goldman Sachs announced its $ 2.2 billion purchase from fintech lender GreenSky, someone placed option deals that immediately appreciated.

On September 14, the trader bought 8,000 options, according to market participants, which would only pay off if GreenSky’s price rose above $ 10. The options were out of the money – meaning GreenSky was trading well below the strike price – and only cost one nickel per share.

After the deal was announced, the value of the contracts, each of which provided for the purchase of 100 GreenSky shares, soared. The trader made a staggering 3,900% gain in a single day on contracts that expire on September 17th, market sources say. That means that a $ 40,000 bet would have become about $ 1.6 million.

Acquisitions are complicated transactions that involve teams of bankers, lawyers, and other specialists with access to market-moving information. With so many glances at a deal, information is often leaked. According to a scientific study from 2014, up to a quarter of all transactions with listed companies result in some form of insider trading, often with calls out of the money in the options market.

Although there have been cases of insider trading that have ensnared high-profile perpetrators, cases of people using tangible, non-public information in the markets, the activity remained in place, according to a 2014 study by professors at the Stern School of Business in New York most unpunished University and McGill University cases.

Goldman Sachs and GreenSky declined to comment on this article. The Securities and Exchange Commission and the Financial Industry Regulatory Authority did not immediately respond to calls for comments.

Goldman was his own financial advisor, using Sullivan & Cromwell as legal counsel. JPMorgan Chase and FT Partners advised GreenSky, which has also engaged law firms Cravath, Swaine & Moore and Troutman Pepper Hamilton Sanders.

GreenSky’s board of directors also retained its own bankers and attorneys at Piper Sandler and Wilson Sonsini Goodrich & Rosati. The banks and law firms declined to comment or did not immediately respond to news.

“Nobody is so lucky”

The September 14th trades weren’t the only unusually predictive bets made prior to the Goldman deal.

Options activity for GreenSky is usually muted, with fewer than 1,000 calls making up average daily volume. However, the stakes on soon-to-be-profitable $ 10 call options have increased in the past two weeks, suggesting that multiple traders may be aware of the deal.

According to Jon Najarian, a veteran trader and CNBC employee, the volume increased from 153 calls on September 7th to 7,175 calls by September 9th. On September 13, two days before the announcement, the call volume reached 12,755. Most of the contracts were sold for a profit on Sept. 15, he said.

“When we see such unusual activity, we tend to think that someone today had tomorrow’s paper,” said Najarian. “Nobody is that lucky. Whoever bought these calls is likely to face regulators.”

The trades were so brazen – some of the calls would expire in a few days – that anyone who made them would have to be inexperienced, according to a former Wall Street executive with more than four decades of knowledge of the market. There are ways to structure the bets that would make them less obvious to regulators, he said.

“This looks like a 22-year-old kid who didn’t know what he was doing,” he said. “But it’s a no-brainer, they had inside information.”

Finance columnist Matt Levine, a former Goldman banker who has written extensively on insider trading, has some guidelines when it comes to the prohibited activities. His first rule (“Don’t do it”) is followed by a second:

“When you have inside information about an upcoming merger, don’t buy short-term out-of-the-money call options on the target,” Levine wrote in a 2014 column. “The SEC will get you!”

– CNBC’s Bob Pisani contributed to this report.

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