OSLO (Bloomberg) Bermuda-based Frontline Ltd, the world’s largest operator of supertankers, jumped 29 percent in two days in Oslo, its biggest such gain since May 2009, on speculation some investors are closing bets on share-price declines.The shares closed up 3.55 kroner, or 8.9 percent, in Oslo yesterday, giving the company a market value of 3.4 billion kroner ($629 million). At one stage, they were up 18 percent, extending a 20 percent advance yesterday.The shares are most likely rising as some investors who bet on declines by selling borrowed stock, are buying them again to return to lenders, three Oslo-based analysts including Ole Stenhagen at SEB Enskilda ASA, said by phone and e-mail today. That practice is called short covering.Frontline and other owners are contending with a supertanker fleet that’s the largest in 29 years and growing at the fastest pace in more than three decades, forcing freight rates to a 14-year low. The two-day advance pared this year’s decline to 71 percent.Erik Nikolai Stavseth at Arctic Securities ASA and Petter Narvestad at Fondsfinans AS also said that short covering was the most likely reason for Frontline gaining both yesterday and today.Jens Martin Jensen, Singapore-based chief executive officer of Frontline’s management unit, said he was “surprised” by the advance. He said August 30, the time for takeovers, was approaching.Charter rates for very large crude carriers, the kinds of ships Frontline operates, may gain if the European Union imposes sanctions on Syrian oil exports, Goldman Sachs Group Inc analyst Edouard Baldini in London, said in an e-mailed report yesterday.Stenhagen at Enskilda said that may have been a catalyst for the shares gaining.