The bank's stock briefly added more than 5.0 percent before falling back to gains of 3.65 percent by 0930 GMT, trading at €11.23 and topping the DAX index of blue-chip German shares.
Banking shares across Europe have benefited from the US Federal Reserve's slight tightening of monetary policy Wednesday, but Commerzbank has gained an additional boost from two days of rumours about its future.
A spokesman for Germany's finance ministry told journalists Wednesday the federal government would not hang on to its 15.6-percent stake in the lender - the legacy of a rescue during the financial crisis - forever.
But he added that "we want to achieve a good result for German taxpayers," a far-off prospect as the value of Berlin's holdings remains well below the €5.1 billion it originally paid.
A financial source familiar with the matter suggested the government might have aimed to jolt some life into Commerzbank's valuation.
"Considerations are still in early stages... we do not expect a large move regarding the Commerzbank ownership in a short time period," ING bank analysts commented.
German business magazine WirtschaftsWoche meanwhile reported Thursday that Berlin favours a future tie-up between Commerzbank and France's BNP Paribas, citing anonymous political and financial sources.
Shares in the French bank gained 1.8 percent to trade at €67.13 in Paris.
BNP declined to comment on the rumours when contacted by AFP.
The French lender is not the only rumoured Commerzbank suitor, with media reports that Italy's UniCredit had expressed interest to Berlin driving up the shares on Wednesday.
Repeatedly the subject of merger or takeover speculation, Commerzbank has for its part always insisted it wants to complete a massive restructuring before considering big new projects.
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