Shares of General Motors fell to a 20 year low amid concerns that a possible change in pension accounting could erase most shareholder equity, Reuters this morning reported. "We have today and tomorrow as the last trading sessions of the year. With the stock being down so far, you would be looking at a little bit of tax selling to harvest those capital losses to offset gains in other areas," Argus Research analyst Kevin Tynan said. "I wouldn't say it's any one issue or any one news item. It's a combination of what's being going on ... with the timing of having two days left," he added. The Wall Street Journal sheds further light on the issue: "In theory, shareholder equity is the value left for investors if a company were to liquidate itself and pay off all of its creditors. No one has said GM is going to do that, but some on Wall Street (and some credit-derivative traders) have bet on a bankruptcy filing."