As of March 15, short interest rose to about 9.980 billion shares, compared with 9.455 billion shares as of Feb. 26.

Investors who sell securities "short" borrow shares and then sell them, hoping the stock will fall so they can buy the shares back at a lower price, return them to the lender and pocket the difference in price.

Shorting can also be part of a hedging strategy.

(Reporting by Caroline Valetkevitch; Editing by Leslie Adler)