By ALEXANDRA SCAGGS

An improving outlook for the energy sector helped pull the Standard & Poor's 500-stock index into positive territory on a day that was heavy with deal activity.

The Dow Jones Industrial Average edged down 9.52 points, or 0.1%, to 13973.39. The S&P 500 gained 1.05 points, or 0.1%, to 1521.38, and the Nasdaq Composite Index added 1.78 points, or 0.1%, to 3198.66.

The Russell 2000 index of small-capitalization stocks closed at a record level, gaining 3.18 points, or 0.3%, to 923.76. The index is up 8.8% this year.

Worries about a possible correction led to a flat markets session in a deal-heavy day. Polya Lesova reports on The News Hub. Photo: Getty Images.

The energy sector tacked on 0.5% to lead the S&P 500, as drilling and oil-services companies jumped. Halliburton (HAL), advanced $2.48, or 6.1%, to $43.32, and Nabors Industries (NBR) added 76 cents, or 4.4%, to 17.92. Goldman Sachs Group told clients in a note Thursday that January marked "a turnaround" in profitability for the group.

Elsewhere in the energy sector, coal company Alpha Natural Resources (ANR) rose 1.18, or 14%, to 9.67, after its latest results beat Wall Street expectations. Peabody Energy (BTU), another coal company, gained as well, advancing 1.08, or 4.5%, to 25.01.

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In deals news, H.J. Heinz (HNZ) soared 12.02, or 20%, to 72.50, after the company agreed to be acquired by an investment group, including Warren Buffett's Berkshire Hathaway (BRKB) and private-equity firm 3G Capital. Berkshire's Class B shares edged up 1.24, or 1.3%, to 99.21.

US Airways Group (LCC) fell 67 cents, or 4.6%, to 13.99, after the air carrier and AMR, the parent of American Airlines, formally announced merger plans.

Hank Smith, chief investment officer of Radnor, Pa.-based Haverford Trust, was heartened by news of the deals. "There is so much cash [available]…With the lack of fear-inducing headlines, some confidence is starting to emerge" that deals won't fall flat, said Mr. Smith, whose firm oversees $6.5 billion in assets.

In other deals news, Constellation Brands (STZ) surged 11.87, or 37%, to 43.75, after agreeing with rival Anheuser-Busch InBev on revised terms of A-B InBev's divestiture of Grupo Modelo (GMODELO.MX)'s U.S. assets. Anheuser-Busch climbed 3.90, or 5.9%, to 69.59.

Artio Global Investors (ART) jumped 69 cents, or 34%, to 2.74, after agreeing to be acquired by the U.K.'s Aberdeen Asset Management (ADN.LN) for $175 million.

In the economic arena, initial claims for U.S. jobless benefits fell more than expected during the latest week from the previous week.

European markets were broadly lower, with the Stoxx Europe 600 falling 0.2%, after euro-zone gross domestic product contracted more than expected in the fourth quarter. The bloc's two largest economies, Germany and France, also shrank by more than expected. Germany's DAX index dropped 1% and France's CAC-40 shed 0.8%.

European economic weakness "continues to be worrisome," said Mark Luschini, chief investment strategist with Janney Montgomery Scott, which oversees $2.6 billion in its asset-management arm. "I think it put pressure on equity markets here in the U.S."

Asian markets generally rose as the Bank of Japan left its monetary policy unchanged and said the economy appeared to have stopped weakening. That helped offset data showing Japan's GDP contracted slightly in the fourth quarter, versus expectations of a slight increase.

Japan's Nikkei Stock Average gained 0.5%, and Hong Kong's Hang Seng Index, which reopened after an extended holiday weekend, rose 0.9%. Mainland Chinese markets remained closed for the Lunar New Year holiday.

Crude-oil prices rose 0.3%, to settle at $97.31 a barrel, while gold pulled back 0.6%, to settle at $1,634.70 a troy ounce. The dollar advanced against the euro and edged lower against the yen. The yield on the 10-year Treasury note fell to 2.000% as prices rose.

In other corporate news, Dow component Cisco Systems (CSCO) fell 15 cents, or 0.7%, to 20.99, after the networking company reported better-than-expected second-quarter earnings but provided a somewhat downbeat outlook.

General Motors (GM) declined 92 cents, or 3.2%, to 27.75, after the car maker's earnings fell just short of analyst expectations.

PepsiCo (PEP) gained 78 cents, or 1.1%, to 72.28, after the beverage and snack company reported better-than-expected fourth-quarter earnings and revenue and boosted its dividend.

Angie's List surged 3.24, or 24%, to 16.86, after the reviews-based website reported a fourth-quarter profit, while analysts had anticipated a loss.

Stamps.com (STMP) slumped 4.08, or 15%, to 23.82. The Web-based postage-services company's fourth-quarter earnings topped estimates, but revenue and its 2013 outlook missed forecasts.

Zillow (Z) leapt 3.33, or 8.5%, to 42.30, after the real-estate website reported a fourth-quarter profit versus expectations of a break-even quarter, along with better-than-expected revenue.

Write to Alexandra Scaggs at alexandra.scaggs@dowjones.com