The S&P energy index was the biggest gainer among the 11 major S&P sectors, rising 2 percent, as U.S. crude was boosted by Venezuela's deepening economic crisis and a looming decision on whether the United States will re-impose sanctions on Iran.
Apple was up 1.2 percent, continuing to ride on news that Berkshire Hathaway's Warren Buffett had boosted stake in the company.
Shares of AthenaHealth jumped 25.2 percent after hedge fund Elliott Management proposed an all-cash offer that would value the healthcare IT company at about $6.5 billion.
At 9:50 a.m. EDT the Dow Jones Industrial Average was up 167.53 points, or 0.69 percent, at 24,430.04, the S&P 500 was up 15.01 points, or 0.56 percent, at 2,678.43 and the Nasdaq Composite was up 52.66 points, or 0.73 percent, at 7,262.28.
Major U.S. stock indexes ended up more than 1 percent on Friday after weaker-than-expected U.S. wage growth numbers calmed investor fears about rising interest rates and inflation.
U.S. corporates have performed strongly in the first quarter, with nearly 80 per cent of the 400 S&P 500 companies that have reported so far topping profit estimates, according to Thomson Reuters I/B/E/S.
That is well above the long-term average of 64 percent and the average of 75 percent over the past four quarters.
Starbucks rose 0.3 percent after Swiss food giant Nestle said it would pay the world's biggest coffee chain $7.15 billion for the rights to sell its products around the world.
Tyson Foods Inc fell 0.6 percent after the meat processor missed Wall Street estimates for quarterly profit as it was hit by higher freight costs and wages.
Advancing issues outnumbered decliners for a 1.88-to-1 ratio on the NYSE. Advancing issues outnumbered decliners by a 1.64-to-1 ratio on the Nasdaq.
The S&P index recorded 18 new 52-week highs and 1 new lows, while the Nasdaq recorded 61 new highs and 6 new lows.