US stocks opened Monday a busy week of corporate earnings sharply lower as oil prices slumped to fresh multi-year lows.
The Dow Jones Industrial Average dropped 96.53 points (0.54 percent) to 17,640.84.
The broad-based S&P 500 sank 16.55 (0.81 percent) to 2,028.26, while the tech-rich Nasdaq Composite Index tumbled 39.36 (0.84 percent) to 4,664.71.
European benchmark Brent oil closed below $50 a barrel for the first time since April 2009 following a gloomy petroleum-market forecast from Goldman Sachs.
Energy equities fell sharply, including Dow member Chevron and Marathon Oil, by 2.2 percent and 5.1 percent, respectively.
"The market is nervous about lower energy prices and whether they are forecasting a slowdown in global economic growth, and not just a supply-demand imbalance," said Sam Stovall, chief investment strategist at S&P Capital IQ.
NPS Pharmaceuticals bolted 8.2 percent higher after announcing plans to be bought by Ireland-based Shire for $5.2 billion.
Animal-health company MWI Veterinary Supply gained 8.2 percent on news it will be acquired by pharmaceutical distributor AmerisourceBergen for $2.5 billion. AmerisourceBergen lost 2.2 percent.
Drugmaker Bristol-Myers Squibb advanced 3.1 percent on news that a study for its Opdivo lung cancer drug was stopped because an independent panel found that the medicine succeeded in improving survival rates in patients.
Biotech company Celgene tacked on 2.9 percent as it projected 2015 sales of $9-$9.5 billion, a 22 percent increase from last year.
Jewelry chain Tiffany slumped 14.0 percent as it said sales during the key holiday period fell one percent from last year, with an especially weak performance in Japan. Chief Michael Kowalski characterized the results as "disappointing overall."
SanDisk, which manufacturers data storage products in consumer electronics, lost 13.9 percent after announcing that it expects fourth-quarter sales of $1.73 billion, down from a previous forecast for $1.80-$1.85 billion.
Bond prices rose. The yield on the 10-year US Treasury fell to 1.91 percent from 1.96 percent Friday, while the 30-year declined to 2.49 percent from 2.54 percent. Bond prices and yields move inversely.