"Unidentified perpetrators" have forced the shut-down of Libya’s largest oil field again, only nine days after it restarted. The battle for Tripoli is seeping out of the capital and closer to the oil-rich Sirte basin threatening further outages.

After restarting El Sharara output on 21 July following the forced closure of a valve by an “unidentified group” two days earlier, Libya’s NOC was once again forced to shut-down output at its largest field on 30...