Their output today, of some 27.5m b/d, is much the same as it was in the 1970s. What is more, they are scarred by the memory of the 1980s, when slower-than-expected growth in demand and a glut of non-OPEC supply left them saddled with lots of expensive excess capacity. The high prices of recent years are partly a legacy of that glut, insofar as OPEC, still leery of over-investment, allowed its cushion of spare capacity to dwindle to almost nothing, heightening supply concerns.

Unfortunately for oil consumers, OPEC has little incentive to expand that cushion in the short term. It would, in effect, be spending money to reduce its revenue, since the price of oil would doubtless fall if traders had no fear of future shortages. Dermot Gately, a professor of economics at New York University, has modelled OPEC countries' income at different levels of production. He concluded that any effort on OPEC's part to expand capacity to maintain its market share would only begin to yield higher revenues after 2015, and even then, the increase would be marginal. Given all the uncertainties involved, a rational OPEC planner would probably resolve simply to maintain exports at today's levels rather than add capacity.