Shares of UAL ( UALAQ), parent of United Airlines, plunged 34% on Wednesday as investors come to terms with the fact that the stock will very likely be worthless by the time the airline emerges from bankruptcy. For the last few weeks, shares of the bankrupt carrier have rallied on extremely high volume, despite the fact that United has warned investors that shares will likely be cancelled when the company exits bankruptcy. Over the last two weeks of February, United shares more than doubled, rising from $1.63 on Feb. 13 to $3.54 on Monday's close, with shares peaking at $3.70 intraday. But since the carrier filed its annual report on Tuesday, in which it reminded investors of the risks of investing in the company's shares, the stuck has pulled a dramatic about face. On Tuesday, the carrier fell 19.2% on 15 million shares, more than four times the average daily volume. Investors continued to rush for the exits Wednesday, with United stock down 96 cents to $1.90. More than 16 million shares traded just three hours into the session, close to five times its usual daily volume. Over the last four months, a study of SEC filings show that United executives, employees and institutions have been selling their stock. As TheStreet.com reported in a story on Tuesday , since Nov. 1, United's CFO and executive vice president have sold shares, along with at least five company directors. (Proceeds of those sales went to charity.) The company's employee stock ownership plan has been extremely active as well, reducing its position by more than 80% in the last year, while major institutional players have also sold stock. Investors who buy shares of United are mistaken if they believe they will see the kind of massive gains that shares of AMR ( AMR), parent of American Airlines, saw in 2003. Because of the nature of bankruptcy, current shareholders own stakes in a bankrupt company, whose shares will be cancelled when the carrier is finished restructuring. Once it exits bankruptcy, the revitalized United will create new equity shares in an all-new post-bankrupt company, likely leaving current shareholders with nothing.