S3 Partners put short interest at about 185 million shares, or 29% of float, as of July 16, according to CNBC. "SpaceX has been a rollercoaster for the short sellers, and it has ended up firmly in their favor," Hillerberg said. "We are seeing continuous demand from short sellers building speculative positions since the IPO," Matthew Unterman, head of research at S3 Partners, told CNBC. Starting August 6, insiders may sell up to 20% of their eligible locked-up shares, totaling as many as 911.5 million shares, per CNBC. Related articlesSpaceX short sellers gain $15.5 billion as shares fall below IPO priceGoogle reports $94 billion stake in SpaceX following historic IPOIBM slashes revenue forecast amid slump in data-center mainframe sales