Discord at OPEC is turning into a price war, loosening the cartel’s grip on the oil market and exacerbating a recent steep selloff. Fissures have widened as Mideast turmoil frays political alliances and producers vie for customers amid a flood of oil from the U.S. and slowing growth in Asia. “No one is telling anyone what they are up to,” one Gulf oil official said. Saudi Arabia this week unilaterally lowered the price it charges for crude scheduled for delivery next month—without the typical consultation with other members of the Organization of the Petroleum Exporting Countries, according to OPEC officials. The decision surprised many market watchers, who were expecting the Saudis to cut output to help boost prices, and sent prices hurtling lower.