Opec is stuck in production purgatory. This week saw the group extend its production cuts into a fourth year, and the current market outlook indicates that a further extension will be required. While the production cuts are succeeding in propping up prices, Opec is paying a heavy price: market share.

In the end, the 24-member Opec+ coalition agreed on 2 July to extend its 1.2mn b/d production cuts by nine months to 31 March 2021. “The commitment to a nine-month extension is...