The European Union and the International Monetary Fund have agreed to create a nearly $1 trillion rescue fund to support European nations burdened by heavy debt.
Markets plummeted last week on fears that Greece's debt problems would upend a global economic recovery.
The Dow Jones industrials are up 404.71 at 10785.14, its biggest gain since March 2009.
The Standard & Poor's 500 index is up 49 at 1,160. The Nasdaq composite index is up 109 at 2,375.
About 3,000 stocks rose and about 150 fell at the New York Stock Exchange. Volume totaled 1.9 billion compared with 2.4 billion Tuesday.