Opec, the Organization of Petroleum Exporting Countries, has certainly been the subject of much criticism for many years.
President Trump recently accused the group of "uprooting the rest of the world" and maintaining "artificially high" oil prices.
He was sometimes accused of ransom of the world, especially in the mid-1970s, when he reduced his stocks and tripled his prices.
But as OPEC energy ministers gather in Vienna, does the group still exert this influence?
They are joined by non-member oil producing countries, notably Russia.
The group wants to stabilize or increase crude oil prices, which fell sharply in early October.
Its main tool is to manage its own production levels, either by reducing whether it wants to raise prices, or by increasing inventories if it wants prices to fall, at least to the point where prices would collapse. not.
Opec's presence in the market is certainly sufficient to make an impact.
It accounts for more than 40% of the world's crude oil production.
It was higher – more than half in the early 1970s – but the current figure remains considerable.
But the remaining 60% of the industry also count.
Two non-OPEC countries are of particular importance in different ways: Russia and the United States.
Influence of Russia
Russia has contributed to Opec's current efforts to raise prices.
It started in 2016 with a decision by OPEC "to implement a production adjustment", which means a reduction of 1.2 million barrels a day.
Crucially, Russia and a number of other non-OPEC members joined in this effort by pledging to limit their production.
Subsequently, prices rose with the main international price, Brent Crude, reaching $ 86 (£ 67) per barrel in early October – it was below $ 50 per barrel in the run-up to that decision.
This does not mean that the decision of OPEC and its partners was the only factor.
The political turmoil in the countries of OPEC, Venezuela, Libya and Nigeria, prevents them from producing the amount of oil possible in theory.
Sanctions of Iran
Iran has been struck by the reimposition of US sanctions on its nuclear program.
The possibility that Iran's oil is not available on the world market – or that it is less – has been an important factor that pushed up prices this year.
But some of Iran's biggest customers – China, India and Japan – have benefited from temporary exemptions and can continue to buy Iranian oil for now without being affected. by the action of the United States.
As a result, prices actually fell as demand for oil from other producers was lower than expected.
That said, the rise in prices since the end of 2016 is due to the agreement reached between OPEC, Russia and other countries.
In OPEC, Saudi Arabia has been key.
According to estimates of the International Energy Agency, Saudi Arabia accounts for more than a third of OPEC's total production capacity and more than half of the unused capacity of the group.
This is an indicator of the extent to which production is restricted.
As important as Saudi Arabia was, she was reluctant to act alone with regard to prices.
He expected, as he usually does, that other members of OPEC would make sacrifices, but he also wanted Russia to be involved.
The largest American producer
There is a third major player in the global sector. the United States, currently the largest producer of all.
The United States is a beast very different from the others.
Oil is produced by the private sector that makes decisions based on what is profitable.
The major Russian oil companies are close to the government and the dominant Saudi Arabian company – Saudi Aramco – belongs to the state.
US oil producers do not cooperate with OPEC to manage prices because it would be illegal under antitrust law or US competition.
But something has happened in the United States in the last decade or so that has transformed the global industry: the rise of shale oil.
There are two important aspects to this.
Impact of shale oil
The exploitation of a relatively new type of resource has reversed the long-term decline in US oil production.
The country still has to import oil. But now he can support two-thirds of his own needs whereas a little over a decade ago, it was a third.
In addition, shale can react more quickly to a changing market.
It does not need as large investments as conventional oil. The investor can recover his money much faster, so that shale production can be increased more quickly when prices start to rise.
Shale was one of the reasons why oil prices fell sharply after mid-2014.
One of the possible reasons why OPEC has not reacted earlier was the desire of some members, notably Saudi Arabia, to see American producers of shale rinsed by prices. lower.
Opec is still important, but it is far from fully in charge of the global oil market.
And in the longer term, if global efforts to combat climate change mean that we are becoming less dependent on oil – a big if not – then Opec will be much less important.
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