The leftist, anti-bailout Syriza party won decisively in Greek parliamentary elections on Sunday, after running a campaign promising to take on Greece's international lenders and bring about an end to austerity measures.

While the United States has limited direct exposure to Greece's relatively small economy, extended volatility in the region could hurt multinational companies.

"There was a lot of trepidation in the market going into the Greek election ... but by this morning the Syriza win was priced into the market already," said Robert Francello, head of equity trading for Apex Capital in San Francisco.

Energy stocks led gains on major U.S. indices after Abdulla al-Badri, OPEC's secretary-general, told Reuters on Monday that oil prices may have reached a floor and could move higher very soon.

Chevron (>> Chevron Corporation) added 1.9 percent to $108.88 while Exxon Mobil (>> Exxon Mobil Corporation) gained 1 percent to $91.76 as the biggest lifts to the S&P 500. The S&P energy index <.SPNY> rose 1.4 percent.

The Dow Jones industrial average <.DJI> rose 6.1 points, or 0.03 percent, to 17,678.7, the S&P 500 <.SPX> gained 5.27 points, or 0.26 percent, to 2,057.09 and the Nasdaq Composite <.IXIC> added 13.88 points, or 0.29 percent, to 4,771.76.

In deal news, Rock-Tenn Co (>> Rock-Tenn Company) and MeadWestvaco Corp (>> MeadWestvaco Corp.) said they would combine to form a packaging company worth $16 billion, with MeadWestvaco shareholders owning a majority stake.

Rock-Tenn shares jumped 6.1 percent to $66.85 while MeadWestvaco surged 14 percent to $51.35 as the S&P 500's biggest percentage gainer.

D.R. Horton Inc (>> D.R. Horton, Inc.) climbed 5.5 percent to $24.38 after the homebuilder's revenue growth beat expectations, boosted by home deliveries. An index of homebuilder stocks <.HGX> rose 1.9 percent.

With 19 percent of S&P 500 companies having reported earnings, 71.6 percent have topped expectations, while 54.7 percent have beaten revenue forecasts, according to Thomson Reuters data. That compares with the long-term average of 63 percent for earnings and 61 percent for revenue.

Ocwen Financial Corp (>> Ocwen Financial Corp) jumped 8.8 percent to $6.91 after the company paid $2.5 million in penalties to the California Department of Business Oversight, which had threatened to suspend Ocwen's license to operate in the state. About 32 million Ocwen shares exchanged hands, making it one of the New York Stock Exchange's most active.

After the closing bell, Microsoft (>> Microsoft Corporation) shares lost 3 percent to $45.60 while United Technologies (>> United Technologies Corporation) fell 2.5 percent to $115.80 after their quarterly results.

NYSE advancers outnumbered decliners 2,111 to 952, for a 2.22-to-1 ratio; on the Nasdaq, 1,785 issues rose and 987 fell, for a 1.81-to-1 ratio.

The S&P 500 posted 38 new 52-week highs and 8 new lows; the Nasdaq Composite recorded 80 new highs and 58 new lows.

Volume was light, with many market participants leaving early due to a massive snowstorm hitting the U.S. Northeast. About 6.27 billion shares traded on U.S. exchanges, below the 7.26 billion average this month, according to BATS Global Markets.

(Reporting by Chuck Mikolajczak; Editing by Nick Zieminski)

By Chuck Mikolajczak