The Standard & Poor's 500 index rose 10 points, or 0.6 per cent, to 1,972 as of 12:15 p.m. Tuesday. The Dow Jones industrial average gained 57 points, or 0.3 per cent, to 16,876.
Investors are watching quarterly results roll in this week from a large group of companies. They are also waiting for Wednesday's policy announcement from the Federal Reserve, which could offer clues about the central bank's plans for raising interest rates. The Fed is also winding down its $4 trillion bond-buying program.
Amgen rose 6 per cent after announcing better-than-expected earnings. Twitter dropped 10 per cent after the company reported results that raised concerns about its user growth and holiday revenue.