“Opec might die,” admitted Iranian oil minister Bijan Zanganeh to a pack of reporters at the crude cartel’s meeting in Vienna last week. “It has lost its authority and it is on the verge of collapse.”

The oil price barely flinched after the 14-nation group announced a nine-month extension to production cuts propping up prices.

Opec’s market-moving power appears to be waning and forecasters expect its share of global production to sink to its lowest level in almost three decades.

In a sign of its slipping grip on the market, the latest price-boosting measures appeared to be pre-announced by Russian president Vladimir Putin at the G20 summit in Japan the weekend before the Opec meeting.

Putin revealed that Russia, a country not in Opec, had agreed with cartel kingpin Saudi Arabia to extend the output caps. “I believe Opec is going to die with these processes,” warned Zanganeh on the rising dominance of Russia and arch-rival Saudi Arabia.

The group which includes major producers such as Saudi Arabia, Iran, Iraq and Venezuela brings together regional foes, two-fifths of global crude production and more than 80pc of the world’s proven reserves with the common aim of controlling oil prices to maximise market share and revenue.