Investors can't shake their worries that economy won't be able to lock in a recovery by the end of the year.
Stocks finished mostly lower after zigzagging Wednesday as a mixed outlook on the economy from the International Monetary Fund and falling commodity prices added to a downbeat mood.
Another tumble in oil prices dragged energy shares lower and reflected concerns that demand for resources will remain weak as the economy struggles.
The IMF said Wednesday it expects the world economy to shrink by 1.4 percent in 2009, slightly worse than its earlier estimate of 1.3 percent. But it boosted its estimate for global economic growth in 2010 to 2.5 percent, up from its April projection of 1.9 percent.
Meanwhile, oil prices fell for a sixth straight day, dropping $2.79 to settle at $60.14 a barrel, tumbling sharply from an eight-month high of $73 in just one week.
In other signs of investor unease, bond prices and the dollar both rose sharply.
Stocks drew some support from a strong auction of 10-year Treasury notes. That helped allay one of the market's recent worries, that the government would have trouble finding enough buyers for the massive amount of debt it's issuing. Investors also flocked to the safety of government debt because they are worried about the economy.