Whiting Petroleum Corp., the top oil producer in North Dakota, plans to keep 11 drilling rigs operating through 2016, though it would add “a couple of rigs” if crude prices rise to $70 a barrel, its chief executive said on Thursday. The comments from CEO Jim Volker were among the most definitive yet from a leader of a big crude producer on what threshold is needed to start fresh drilling and curb recent pullbacks that have rocked the oil sector since prices started to drop last summer. Thus far this quarter, executives at industry peers have sent mixed messages on adding new rigs. Hess Corp, for example, does not plan to add any rigs this year, while Pioneer Natural Resources Co told Reuters last week that it was considering adding rigs in the near future. Oil prices have gained more than 15 percent […]