Porsche rose the most in more than 16 months in Frankfurt after a US judge dismissed two lawsuits claiming the sports-car maker misled short-sellers in its acquisition of Volkswagen shares in 2008.
Porsche's preferred stock climbed as much as €6.88, or 12pc, to €66.54, the biggest intraday jump since August 14, 2009, valuing the company at $11.6bn.
US District Judge Harold Baer in Manhattan dismissed the complaints filed by hedge funds Elliott Associates and Black Diamond Offshore and representing a total of 39 US and foreign-based funds.
The suits claimed Porsche cost hedge funds more than $2bn by secretly cornering the market in VW shares. Stuttgart, Germany-based Porsche is now merging with Volkswagen, Europe's largest automaker.
"Porsche has cleared an important interim hurdle on its way toward merging with Volkswagen," said Marc-Rene Tonn, an analyst with M.M. Warburg who recommends holding the stock. "The VW-Porsche combination has become more likely following the US ruling."
VW CEO Martin Winterkorn said last November that the merger may stall until tax disputes in Germany and lawsuits in the US are resolved.