Volkswagen shares jumped nearly 90 percent today, on a day that saw a Dow jump of almost 900 points as well. However, Volkswagen AG was also up 150 percent the previous day. How? Porsche announced on Sunday that they had upped their stake in the company to 42.6 percent, and had plans to increase it's holdings to 75% in 2009, but that's not the whole story.
Rumor has it (aka, I heard on CNBC...) that the gigantic run was due in part to hedge funds being short squeezed. At one point, Volkswagen became not just the most valuable automaker, but the most valuable company on the planet (momentarily besting Exxon Mobil). The Financial Ninja has covered this story in depth if you're looking for more details.