India, May 3 -- The United Arab Emirates (UAE) left the Organisation of the Petroleum Exporting Countries (OPEC) on May 1, ending a 59-year membership without consulting Riyadh, Moscow or anyone else. The cartel's most senior officials learned of the decision on the wires. The oil price barely moved. That, more than the announcement itself, is the story. In the age of US shale and a closed Strait of Hormuz, OPEC's power to influence prices is no longer what it once was. Abu Dhabi has chosen to leave a grouping whose collective discipline has, for some time now, delivered diminishing returns to its most capable members.

The proximate reasons are well documented. Abu Dhabi has spent more than $150 billion to lift the capacity of the Abu Dh...