Jan. 2 (Bloomberg) -- Shares of Metro AG, Europe's third- largest retailer, posted their steepest gain in more than three years on speculation that one of the German company's founding families may make a takeover offer.

The stock rose 2.75, or 5.7 percent, to 51.06 euros in Frankfurt, the biggest one-day advance since September 2003. The gain boosted the Dusseldorf-based company's market value to about 16.7 billion euros ($22.2 billion).

``Rumors the Haniel family might want to completely take over the company are boosting the stock,'' said Christof Ruemmelein, a trader at Merck Finck & Co. in Munich. The family, which owns about 18.5 percent of Metro's shares, isn't buying stock in the retailer, spokeswoman Jutta Stolle said today.

About 50 percent of the company's shares are owned by three founding families. In addition to the Haniel stake, the Otto Beisheim family owns about 18.5 percent and the Schmidt- Ruthenbeck family holds about 13 percent of Metro's stock.

``I didn't expect takeover speculation to reaccelerate that quickly after the holidays, but if you look at the share price, this seems to be a little more than just a rumor,'' said Frank Schallenberger, an equity strategist at Landesbank Baden- Wuerttemberg in Stuttgart, Germany. ``M&A will remain a driver of the stock markets in 2007.''

Metro spokesman Juergen Homeyer said the company won't comment on market speculation. Stolle, who normally speaks for the three families, said the ownership structure won't change and Beisheim and Schmidt-Ruthenbeck don't plan to sell shares.

Today's gain in the retailer's stock is the biggest in Germany's benchmark 30-member DAX Index. Metro shares rose 18 percent in 2006 compared with a 22 percent gain by the DAX.

Last September, the Schmidt-Ruthenbeck family sold a 5.39 percent stake worth about $1 billion in the company, causing the stock to drop 3.8 percent. The three major shareholders didn't plan to further sell shares, Stolle said at the time.

To contact the reporter on this story: Aaron Kirchfeld in Frankfurt at akirchfeld@bloomberg.net; Andreas Hippin in Frankfurt at ippin@bloomberg.net

Last Updated: January 2, 2007 12:41 EST