Opec this week notched up a couple of achievements. It appointed a new Secretary General. And re-admitted Gabon. But to what end?

In a rare show of relative unity, OPEC on 2 June at the oil producers’ 169th meeting in Vienna announced the appointment of a new secretary general and confirmed the re-entry of Gabon, just six months after former member Indonesia rejoined.

The group sees the appointment of Nigeria’s Muhammed Barkindo, effective 1 August, to the post of Secretary...