By David Russell, reporter at OptionMonsterNEW YORK -- Frontline ( FRO) has been falling for the last three years, but the bulls took the helm on Friday. OptionMonster's monitoring systems detected heavy call volume in the oil-tanker company, with some 2,700 of the June 2 contracts purchased against previous open interest of just 205. Premiums started at 15 cents and then doubled to 30 cents as the shares advanced. Calls lock in the price where investors can buy stock, and they can deliver significant leverage because they're so cheap to buy. Traders often uses them to keep a trade from running away from them while reducing the amount of capital at risk. Frontline shares surged 12% to $1.97 on Friday. The stock fetched more than $35 in April 2010 before a slowing global economy took the wind of out its sails. In recent weeks, however, numbers from China and Europe have surprised to the upside and sentiment has warmed toward emerging-market stocks. That could be bullish for a transport such as Frontline. Short interest also stood north of 20% in mid-April, which could also squeeze the shares higher. Total option volume was 16 times greater than average in Friday's session, with calls outnumbering puts by a similar proportion. Russell has no positions in FRO.