Opec opted to extend its output curbs to March 2018 when it met in Vienna on 25 May alongside ten non-Opec producers in its efforts to rebalance the market. But whether the strategy is working in the face of rebounding US shale output is up for debate.

The original six-month Opec/non-Opec cut agreement had been set to expire on 1 July. It was intended to take around 1.8mn b/d of supply away from the market – 1.2mn b/d from Opec and 558,000 b/d from non-Opec partners (MEES, 16 December...