Bearish bets against the United States Oil Fund, which trades under USO, increased as crude prices tumbled. : As smaller investors pile into the risky and troubled United States Oil Fund, hedge funds are taking the other side of that trade and making a lot of money. Over the last two months, as the fund — which trades under the ticker USO — plunged 75%, those who bet against it by short selling pocketed hundreds of millions of dollars. According to data from S3 Partners, from Feb. 27 to April 21 "short sellers went into overdrive."