A famed Bordeaux vintner extended its offer to buy California winemaker Chalone Wine Group ( CHLN).

Napa-based Chalone said Tuesday that Domaines Barons de Rothschild extended through Sept. 10 its offer to acquire Chalone for $9.25 a share in cash. Domaines Barons de Rothschild, which owns 46% of Chalone and operates a joint venture with the company, initially made the offer in May and has since extended it several times. But with the stock trading about 13% above the offering price, the deal faces long odds.

The back-and-forth comes as investors speculate about the prospect for a bidding war for Chalone, which makes wine under its own name as well as under the Acacia, Provenance, Hewitt, Jade Mountain, Moon Mountain, Dynamite, Orogeny and Echelon brands.

Domaines Barons de Rothschild, which owns the Chateau Lafite-Rothschild winery in France, bid $9.25 for the shares it didn't already own at a time when Chalone was trading for $8 and change. But Chalone stock surged into the double digits when the company's second-largest shareholder, Phyllis Hojel, indicated she would engage third parties to discuss alternative transactions, Thomson Media's Mergers & Acquisitions Report reported in July.

Chalone's board has formed an independent panel to consider the bid. In July, Chalone entered standstill and confidentiality agreements with Domaines Barons de Rothschild and Constellation Brands ( STZ), a distribution behemoth that Domaines Barons de Rothschild intends to link up with for the Chalone buyout.

Chalone became the first publicly traded U.S. winemaker following its 1984 Nasdaq IPO. Later, Chalone began a partnership with Domaines Barons de Rothschild covering the Chateau Duhart-Milon winery in Pauillac, Bordeaux.

On Tuesday, Chalone fell 3 cents to $10.43.