Sept. 19 (Bloomberg) -- Ford Motor Co. Chairman William Clay Ford Jr. sold 1 million common shares for $5.05 million yesterday, according to a U.S. regulatory filing.

Bill Ford, 51, sold the shares, at an average price of $5.05, to retire debt incurred in exercising options, company spokesman Mark Truby said in an interview. The chairman declined a salary when he was chief executive officer for five years through September 2006 and received the options instead.

``It's a puzzle,'' said David Healy, an analyst with Burnham Securities Inc. in Sierra Vista, Arizona. ``He's been pretty public in supporting the turnaround of Ford, optimistic on that front.''

Bill Ford has overseen an 91 percent decline in the value of the automaker's stock since he became chairman almost 10 years ago. The great-grandson of the company founder yielded the CEO post to Alan Mulally, recruited from Boeing Co. two years ago to stem losses that have totaled $23.9 billion since 2005.

Bill Ford now directly holds 4,956,971 common shares, according to the filing. Accounting for the 398,920 shares held indirectly, the sale represents 16 percent of his common shares.

The price ranged from $5 and $5.095. The average sale price is about 16 percent below the average of $6.03 for Ford Motor common shares this year.

The chairman also owns about 3.8 million Class B shares, Truby said. The 70.9 million Class B shares held by the family give it 40 percent of voting power at the second-largest U.S. automaker.

Ford gained 1 cent to $5.29 at 4:15 p.m. in New York Stock Exchange composite trading. The shares lost 21 percent this year. The U.S. filing was released after the close of regular trading.

To contact the reporters on this story: Bill Koenig in Southfield, Michigan, at wkoenig@bloomberg.net; Greg Bensinger in New York at gbensinger1@bloomberg.net

Last Updated: September 19, 2008 18:36 EDT