Facebook stock could have as much 1.9 billion more shares up for public sale soon, but only if insider executives decide to sell their own shares. It seems that the customary 90 day stock lockup period after an IPO(initial public offering) is ending soon, possibly making many more shares of the stock available on the market. Often, new stocks are locked up by companies who wish to avoid a situation of wild market fluctuations if giant blocks of stocks soon get sold by some of company insiders such as employees who received stock in trade for part of their salary.
Facebook debuted at $38 a share about 90 days ago as an IPO, but was only trading around $21 today. If there is a big volume of shares sold after Thursday, then the stock could once again take wild market fluctuations.