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Near 8:02 a.m. ET, Dow futures were up 65 points (0.37%), S&P 500 futures were up 9 points (0.47%), and Nasdaq futures were up 22 points (0.51%).
Stocks gained strong on Monday, with the Dow rising by as many as 270 points, after weekend polls signaled a remain decision.
On Thursday, Britons will decide on their country's continued membership in the European Union. Those in favor of a remain vote are concerned, in part, about the economic risks the UK's exit could pose to the region and to itself. A poll from the Telegraph on Tuesday showed the "Remain" camp had a 7-point lead, or 53% to 46%.
The British pound is stronger by 0.3% at 1.4729 after surging to 1.4760 earlier - a new high for 2016.
Besides the odds of a Brexit, investors will be closely following the first day of Federal Reserve chair Janet Yellen's testimony on Capitol Hill. At 10 a.m. ET, she will appear before the Senate Banking Committee for her semiannual 'Humphrey Hawkins' testimony, and will speak before the House Financial Services Committee on Wednesday.
The economic-data calendar is otherwise empty today.
Gold fell 1.16%, or $14.95 an ounce, to $1,277.15. West Texas Intermediate crude oil futures fell 1.58% to $49.17 per barrel ahead of inventory data after the closing bell.