Stocks advanced as a series of merger deals excited investors, pushing the blue-chip indices to two-and-a-half-year highs in the absence of significant economic news.

The Dow Jones Industrial Average gained 69.48 points, or 0.57 percent, at 12,161.53. The S&P 500 Index climbed 8.18 points, or 0.62 percent, to 1,319.05. The Nasdaq Composite Index added 14.69 points, or 0.53 percent, at 2,783.99.

AOL Inc (NYSE:AOL) agreed to buy The Huffington Post for $315 million.

Oil driller EnsCo Plc (NYSE:ESV) agreed to buy Pride International Inc (NYSE:PDE) for about $7.3 billion; while diversified industrial company Danaher Corp (NYSE:DHR) agreed to purchase medical diagnostics company Beckman Coulter Inc (NYSE:BEC) for about $6.8 billion.

Treasuries rose somewhat as the yield on the 10-Year Treasury slipped to 3.644 percent.

Oil futures plunged almost 2 percent, while gold future edged up to $1351.10 per ounce.