This past week was a turbulent one for investors in Bristow Group (NYSE: BRS), Oasis Petroleum (NYSE: OAS), and Nordic American Tankers (NYSE: NAT). Those oil stocks got hammered after announcing moves to shore up their balance sheets and business prospects because they paid a high price to do so. That steep price will make it harder for them to create value for investors in the future. Oil tanker company Nordic American Tankers was the worst performer in the group, plunging nearly 27% on the week.