The main indexes pared opening gains of more than 1.5 percent as investors weighed a spate of corporate earnings reports and mostly upbeat economic data.

By noon, the Dow was up 161.66 points (1.28 percent) at 12,837.71.

The S&P 500 rose 14.69 points (1.10 percent) to 1,352.58. The Nasdaq was up 24.77 (0.87 percent) to 2,571.39.

The normally cautious Draghi gave his most resounding defense of the under-siege currency to date, sending markets around the world solidly into positive territory and lifting the euro.

The "ECB is ready to do whatever it takes to preserve the euro. And believe me it will be enough," Draghi told a business summit in London.

"The comments by the central banker sparked speculation the ECB could do additional bond buying to lower soaring yields of Italian and Spanish debt," said analysts at Wells Fargo Advisors.

Dow member ExxonMobil rose 0.6 percent. The energy giant posted a 49 percent profit rise for the second quarter, but missed Wall Street estimates for earnings excluding a one-time gain.

United Continental Holdings, the parent of United Airlines, the world's biggest airline, reported a steep fall in second-quarter profit on weak revenue growth. UAL shares skidded 7.0 percent.

Online game company Zynga plunged 38.5 percent, to $3.13, after reporting a shock $22 million loss for the second quarter.

The poor results for Zynga, which grew out of a game platform on Facebook, helped drive Facebook shares down 5.5 percent. Facebook reports its first quarterly results as a public company after the market closes.

On Wednesday, stocks closed mixed on a mixed batch of big company quarterly earnings reports.

Bond prices fell. The 10-year Treasury yield rose to 1.43 percent from 1.41 percent Wednesday, while the 30-year increased to 2.49 percent from 2.47 percent. Bond prices and yields move in opposite directions.