Merger activity drove the Dow and S&P to two-and-a-half-year highs on Monday in the latest in a series of mileposts that point to more gains ahead.

Buying accelerated after the S&P 500 broke through the 1,313 mark, taking the index further into levels that prevailed before the financial crisis. More than two stocks rose for every one that fell on both the New York Stock Exchange and Nasdaq, but the day's rise came on lighter-than-average volume.

Diversified industrial company Danaher Corp agreed to buy medical diagnostics company Beckman Coulter Inc for about $6.8 billion. Oil driller EnsCo Plc said it would buy Pride International Inc
for about $7.3 billion.

The size of these deals is an indication that the buyers feel comfortable putting that cash to work while the companies being bought are undervalued, said James Dunigan, chief investment officer at PNC Wealth Management in Philadelphia, which oversees $105 billion.

The level of the broader market is reasonable, but there are these individual situations that deserve a higher premium than the market is getting over all.

Danaher Corp rose 2.2 percent to $49.03 while Beckman Coulter gained 10 percent to $82.65. EnsCo fell 4.2 percent to $52.13 while Pride International rose 15.7 percent to $39.80.

With the 1,313 level breached, stocks face little by way of technical resistance until the 1,400 level on the S&P.

The Dow Jones industrial average <.DJI> was up 69.40 points, or 0.57 percent, at 12,161.55. The Standard & Poor's 500 Index <.SPX> was up 8.18 points, or 0.62 percent, at 1,319.05. The Nasdaq Composite Index <.IXIC> was up 14.69 points, or 0.53 percent, at 2,783.99.

The S&P is up 4.9 percent so far in 2011, adding to the gains it notched mostly in the latter half of 2010. The size and swiftness of the advance has prompted many analysts to call for a correction, though none has materialized.

UBS raised its 2011 target for the S&P 500 index by 7.5 percent to 1,425 from 1,325, citing an improving outlook for the economy and earnings.

Loews Corp reported a better-than-expected 16 percent jump in profit, sending shares of the conglomerate up 4.5 percent to $43.27.

About 72 percent of S&P 500 companies that have reported results so far posted stronger-than-expected earnings, according to Thomson Reuters data. Investors expect aggregate earnings rose 37 percent in the last quarter, the highest estimate for that period in more than 10 months.

Speaking to the U.S. Chamber of Commerce, President Barack Obama stepped up efforts to woo the business community, seeking their help to tackle burdensome corporate taxes, but offering no new initiatives.

This was a pretty positive message that shows the President continuing to extend an olive branch to business, Dunigan said.

AOL Inc has agreed to buy The Huffington Post for $315 million. The stock fell 3.4 percent to $21.19.

Volume was light, with about 6.89 billion shares traded on the New York Stock Exchange, the American Stock Exchange and Nasdaq, well below last year's daily average of 8.47 billion.