Stocks are ending sharply lower after a late-afternoon slide.
The losses extended a downturn in the market last week which gave indexes their worst weekly performance in more than two years.
The Dow Jones industrial average slumped 222 points, or 1.4 percent, to close at 16,321 Monday.
The Standard & Poor's 500 index fell 31 points, or 1.7 percent, to 1,874. The Nasdaq fell 62 points, or 1.5 percent, to 4,213.
Energy stocks fell nearly 3 percent, much more than the rest of the market. Investors have been dumping those stocks as the price of oil continues to fall.
The price of oil has been slumping as fears of waning demand grow even as production remains high.