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With no major US earnings or economic data scheduled this week, trading volumes were expected to thin leading up to Thursday's Thanksgiving holiday and an early close on Friday.
"With earnings season now out of the way, macro news and the prospects of tax reform will basically guide the market," said Peter Cardillo, chief market economist at First Standard Financial in New York.
"I don't expect the market to endure any sharp sell-off or sharp gains (today)."
The US House of Representatives passed their version of a tax bill last week. But the Senate, from which it has already faced resistance, is expected to vote on their version of the bill after Thanksgiving.
Any signs of repositioning ahead of the vote would be liable to impact investors' thinking on the bill.
At 9:39 am ET (1339 GMT), the Dow Jones Industrial Average was up 30.76 points, or 0.13 per cent, at 23,389, the S&P 500 was up 1.67 points, or 0.06 per cent, at 2,580.52 and the Nasdaq Composite was up 9.19 points, or 0.14 per cent, at 6,791.98.
Seven of the 11 major S&P indexes were higher, led by gains in telecom services and technology sectors.
Cisco rose 1.5 per cent after brokerage Independent Research raised its price target on the stock.
Cavium jumped 8 per cent after larger rival Marvell said it would buy the company in a deal valued at about $6 billion. Marvell shares also 1.33 percent.
General Motors, up 25 per cent for the year but down almost 7 percent in the past month, inched higher after brokerage Guggenheim upgraded the automaker's stock to "buy".
Wal-Mart was down 1 per cent after Goldman Sachs cut its rating on the stock to "neutral" from "buy". However, fellow Dow member Verizon rose 0.6 percent after Wells Fargo upgraded the wireless carrier's stock to "outperform".
Alibaba gained 1.37 percent after the e-commerce giant said it would invest $2.87 billion in China's top hypermart operator Sun Art.
Health stocks fell, weighed by a 2.25 percent drop in Merck shares after Roche announced two trial wins for its new cancer and haemophilia drugs.
Advancing issues outnumbered decliners on the NYSE by 1,397 to 1,133. On the Nasdaq, 1,382 issues rose and 1,026 fell.