Six Flags Inc. (PKS) on Thursday put itself up for sale and invited Washington Redskins owner and dissident investor Daniel Snyder (search) to take part in the process. But it said it opposed any effort by Snyder to take control of the company outside this process.

The move came in response to the football team owner's announcement last week that he was seeking to replace the chairman and chief executive and raise his stake to 34.9 percent.

Shares rose more than 10 percent, after the theme park operator said it plans to pursue a "prompt" auction process and will invite Red Zone (search), the investment company managed by Snyder, to participate.

Shares rose 65 cents, or 9.9 percent, to $7.19 on the New York Stock Exchange. The stock rose more than 10 percent in earlier trade.

The theme park operator also said it plans to oppose Red Zone's attempt to gain effective control of the company.

"If Red Zone commences a consent solicitation, the board urges Six Flags stockholders not to sign any consent form they may receive from red Zone and will request that sockholders revoke any consent they may give," the company said in a statement.

Matthew Harrigan, an analyst with Janco Partners Inc., said potential buyers would be few and far between. He ruled out larger rival Walt Disney Co. (DIS).

"Disney has a very different business. Disney is a destination parks business, and Six Flags is a regional chain, catering to locals," he said.

Six Flags runs 30 amusement parks, but its properties do not have hotels. The chain's revenue and profit have lagged behind in recent years -- it posted a profit in the most recent quarter, but has reported annual losses since 1999.

Bill Gates, founder and chairman of Microsoft Corp. (MSFT), said last year that he had owned Six Flags shares for years and was dissatisfied with the company's performance.

Snyder, a major critic of the company's management, has said he is seeking to replace Chairman and Chief Executive Kieran Burke and appoint Mark Shapiro, an executive at Walt Disney Co.'s ESPN unit, as chief executive.

He has also said he wants to appoint himself as chairman.