Shares of Teekay Offshore Partners (NYSE: TOO) plunged on Thursday, down more than 15% at 3:15 p.m. EDT. Driving the sell-off was the company’s first-quarter report, during which earnings fell versus last year because of a contract dispute with Brazilian oil giant Petrobras (NYSE: PBR). That sell-off was a key contributor to its parent company’s double-digit plunge today.