Financial shares in particular were lifted by the news.

Bank of America shares, which on Tuesday fell more than 3 percent, to $5.07, their lowest closing level since March 2009, were up 7.3 percent, at $5.44, on Wednesday. JPMorgan rose more than 8 percent to $30.97. Morgan Stanley was up more than 11 percent at $14.79.

On Wednesday, the Federal Reserve, the Bank of England, the European Central Bank, the Bank of Japan, the Bank of Canada and the Swiss National Bank, trying to bolster financial markets as the euro zone debt crisis grinds on, announced that they would reduce by about half the cost of a program under which banks in foreign countries could borrow dollars from their own central banks, which in turn get those dollars from the Fed. The banks also said that loans would be available until February 2013, extending a previous deadline of August 2012.

The move is intended to free up liquidity and ensure that European banks have funds during the sovereign debt crisis. But some analysts saw it as a stop-gap measure to avoid a looming crisis that some compared to that set off by the collapse of Lehman Brothers in 2008.

“What it does do is take off some of the pressure from this boiling pot,” Mr. White said.

As the exuberance set in and funding pressures appeared to ease, bond prices fell, commodity prices rallied and financial shares soared as investors bought shares on the hope that the central banks had smoothed the way for Europe to take more forceful action in advance of a European summit meeting Dec. 9. The jump in stocks was also an extension of the turmoil and volatility that have characterized global markets for more than a year.

It was unclear even after Wednesday’s move whether banks would loosen up lending or whether the market enthusiasm would last.