Saudi Arabia managed to hold the fragile 24-member coalition of Opec and 10 non-Opec states (Opec+) together during a mammoth set of meetings on 30 November to secure a nine-month extension to production cuts. The stated goal is achieving market stability to reassure both producers and consumers, and encourage renewed upstream investment, particularly in long cycle projects. A lofty ambition. But is it achievable?

The extended deal was labeled an “amendment” to the existing...