Tesla short-sellers have lost $18 billion this year on the stock's 230% spike

• Tesla's stock has rallied this year, gaining as much as 230% on solid vehicle delivery numbers and a slew of Wall Street upgrades.
• In the same timeframe, traders betting against Tesla have notched $18.08 billion net-of-financing mark-to-market losses, according to data from financial-analytics firm S3 Partners.
• A solid part of those losses occured in June and July, according to S3. Tesla short-sellers lost $3.71 billion in mark-to-market losses in June and $4.08 billion in July.
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Traders betting against Tesla have lost billions of dollars this year as the stock surged to multiple fresh highs.

Tesla short-sellers have notched $18.08 billion in net-of-financing mark-to-market losses amid the company's more than 230% rally, according to data released Thursday from S3 Partners, a financial-analytics firm.

The rally was fueled by solid vehicle delivery numbers and a slew of Wall Street analyst upgrades. Next, all eyes will be on the automaker's quarterly profit report July 22.

The last five weeks have been particularly painful for Tesla shorts, accounting for 43% of year-to-date losses, according to Ihor Dusaniwsky, the managing partner of predictive analytics at S3. Tesla short-sellers lost $3.71 billion in mark-to-market losses in June and $4.08 billion in July, S3 data show.

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That's led to some short covering, or traders exiting their positions as the stock climbs, sometimes called a short squeeze.

"The reason behind Tesla's short squeeze is obvious and straight forward, large mark-to-market losses are forcing out some short sellers as they hit their loss limit thresholds," Dusaniwsky wrote. Short-sellers have bought-to-cover 1.7 million shares in the last month as Tesla surged 44%, according to S3 data.

In the last week, however, there's been a slight lull in short covering, according to S3. Still, the 98,000 shares covered in the last week were worth a "significant" $133 million, said Dusaniwsky.

Tesla is also on the cusp of a short-selling milestone — short interest, or the value of shares shorted, is nearing $20 billion, according to S3. Tesla is likely to be the first company ever to have such a large short interest.