(Bloomberg) -- Investors hanging onto SpaceX shares after a plunge below their IPO price are bracing for the next potential hit, when $101 billion worth of stock becomes available for trading on Thursday. Most Read from BloombergThe scheduled ending of a lockup agreement restricting insider share sales until a specified period after an initial public offering is nothing new. Many are sitting on paper gains, even at prices well below the $135 per share seen in the record $86.2 billion IPO for Space Exploration Technologies Corp., as it's formally known. Ending restrictions on some insiders will more than double the number of shares available, to as many as 1.55 billion shares from about 639 million shares now, according to the IPO prospectus. That skepticism has paid off to the tune of $5.3 billion in paper profits, the data show, after the stock closed 38% below a June 16 closing high before the results.