Stocks rose at the open on Tuesday on easing concerns about the euro zone's economy and after a report showed better-than-expected retail sales last month.

Investor sentiment about economic prospects in Europe was buoyed after euro zone finance ministers gave final approval to a second bailout for Greece and data in Germany showed analyst and investor sentiment rose significantly more than expected in March.

Data in the United States once again indicated a slowly improving domestic economy, as retail sales recorded their largest gain in five months in February, despite rising gas prices.

Just maybe a little bit of a relief with some of that uncertainty out of the way and the retail sales, highest in five months, is helping. It is all good news, said Terry Morris, senior vice president and senior equity manager for National Penn Investors Trust Co in Reading, Pennsylvania.

But Morris cautioned that the trend of low market volume was unsettling, reflecting a lack of commitment from investors.

Monday's volume of 5.24 billion shares traded on the New York Stock Exchange, NYSE Amex and Nasdaq represented the lowest tally of the year.

The mentality has shifted from selling rallies to buying dips, so a lot of people are just sitting there, keeping their powder dry and hoping the market pulls back so they can get in, said Morris.

The Dow Jones industrial average <.DJI> gained 49.72 points, or 0.38 percent, to 13,009.43. The Standard & Poor's 500 Index <.SPX> rose 7.48 points, or 0.55 percent, to 1,378.57. The Nasdaq Composite Index <.IXIC> added 21.39 points, or 0.72 percent, to 3,005.05.

The S&P 500 index reached its highest intraday level since June 2008.

Later in the session, investors will look to the Federal Reserve, which is expected to hold steady on monetary policy when it concludes its one-day meeting, acknowledging a mildly brighter economic outlook while refraining from any suggestion that further easing is now off the table.

Markets were unnerved recently after Fed Chairman Ben Bernanke stopped short of giving a strong signal of more economic stimulus during congressional testimony.

Yahoo Inc sued Facebook Inc over 10 patents that include methods and systems for advertising on the Web, opening a major legal battle among big technology companies in social media. Yahoo edged up 0.4 percent to $14.55.

Great Wolf Resorts Inc jumped 22 4 percent to $5.13 after private equity firm Apollo Global Management said its affiliate will buy the operator of indoor waterpark resorts for about $703 million, including debt.

Midas Inc jumped 27.5 percent to $11.46 after the auto aftermarket repair chain said it would be taken private by TBC Corp for $173 million in cash.

(Editing by Padraic Cassidy)

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