The market has reacted cautiously but positively, with Brent blend back up above $50 per barrel.

There is still scepticism over Opec’s ability to achieve the goal it has set to be ratified at its meeting next month — to cut production from over 33.5 million barrels per day to between 32.5 and 33 million bpd.

The fact that Saudi Arabia and others have swallowed their pride and called for a change of strategy at a summit in Algiers is a boost. However, details on individual quotas remain to be decided.

Equally, relations between key Opec members such as Saudi Arabia, Iran and Iraq remain unpredictable.

A previous attempt to broker new output targets in April foundered when Riyadh refused to cut production as long as Iran demanded the right to keep on pumping.

This time, Riyadh has indicated it would reduce its volumes if Tehran at least holds its output steady.

The credibility of the group is now on the line, and failure to push through with some kind of agreement in November would be very damaging. It would certainly send the price of crude plummeting.

However, even if there is a deal, it will still only have limited impact for a variety of reasons.

Also, Opec members have often signed similar undertakings only to renege on their commitments.

Non-Opec producers are not included of course, even though Russia has promised to hold, if not cut, output.

Moscow is not the most reliable partner in this regard, and a cratering economy means Russia is in dire need of oil revenues.Other major non-Opec producers, such as Norway, Canada and Mexico, will not be changing their strategies.

And what of the US shale drillers? They will be cock-a-hoop at any price rise that results from lower Middle East oil exports.

There has already been a small but significant bounce back in the number of drilling rigs being utilised in recent months. Eleven more units were brought out of storage in the last week of September, according to the latest figures from Baker Hughes.

More rigs will follow if there is any sign that the price of oil is set to remain at levels significantly up on the sub-$30 mark seen in the first quarter of this year.

Meanwhile, the pressure on Opec to act has become intense, with members such as Venezuela close to financial collapse.

Even Saudi Arabia has been suffering. The world’s largest oil exporter recorded a public accounts surplus amounting to 12% of gross domestic product as recently as 2012.

By last year this had turned into a deficit of 16% and encouraged radical plans to cut subsidies and sell off parts of the national oil company, Saudi Aramco.

There has been new thinking in Riyadh, with a modernising Deputy Crown Prince, Mohammad bin Salman Al Saud, in the ascendancy and a new oil minister, Khalid al-Falih. But it is also worth remembering that Saudi oil production reached a record high at nearly 11 million bpd as recently as July.

Meanwhile, there are signs that US shale producers are becoming more efficient, increasing output with fewer wells.

As BoA Merrill Lynch analysts put it: “Opec has called a truce on oil prices, but relentless improvements in shale technology will keep the Saudis awake at night, wondering of they have made the right choice.”