About 35 minutes into trade, the Dow Jones Industrial Average was at 16,482.91, up 29.08 points (0.18 per cent).
The broad-based S&P 500 dipped 0.31(0.02 per cent) to 1,926.51, while the tech-rich Nasdaq Composite Index shed 5.40 (0.12 per cent) to 4,528.67.
Several leading petroleum producers, including Dow member ExxonMobil and ConocoPhillips, edged higher as oil prices rose ahead of the release of US petroleum inventory data.
But Dow member Walmart dropped 4.8 per cent after it cut its fiscal 2017 sales forecast due to store closures and the strong dollar.
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Ingram Micro, which distributes personal computers and other technology products, surged 22.4 per cent on news it agreed to be acquired by China's HNA for USD 6 billion.
Perrigo, which makes over-the-counter pharmaceutical profits, fell 8.9 per cent as it projected 2016 adjusted earnings of USD 9.50 to USD 9.80 per share compared with analyst expectations for USD 9.74 per share.
Nvidia, which provides graphics and other visual computing technology, jumped 8.8 per cent as it reported fourth-quarter net income of USD 207 million, up 7.3 per cent from the year-ago period.