Trader Edward Schreier, right, works on the floor of the New York Stock Exchange Monday, Jan. 5, 2015. US stocks opened lower Monday, led by declines in energy stocks as the price of oil plunged again. (AP Photo/Richard Drew)

Markets stumble as oil dips below $50

A plunge in the price of crude is hitting energy companies and leaving investors fearful that the selling will spread to other industries.