It used to be said of OPEC that it was like a teabag – it only worked in hot water. In a move sources say was masterminded by Saudi Arabia, ministers finally agreed for the first time in decades to drop any reference to the 13-member group’s output ceiling. The pivot, which surprised not only markets but also some OPEC officials, appeared to be a direct response to Saudi Arabia’s arch-rival Iran, which has made clear it intends to make a rapid return to global oil markets next year as nuclear-related sanctions are lifted.