Analysis By Andrew Walker BBC economics correspondent in Vienna

With the price of crude oil sliding since the war in Iraq started, ministers from Opec's member countries came to Vienna desperate to prevent any further decline.

Their agreement to cut crude oil exports by two million barrels a day from 1 June might just achieve that.

The Opec President's comments caused momentary mayhem

But the process of coming to that decision and the various comments of different ministers made this Opec meeting a horribly confusing one for many observers.

Even some Opec officials seemed to have a hard time with it during a news conference.

At one point, the President of the meeting - Abdullah al Attiyah who is the Qatari Petroleum Minister - was asked if there are official quotas for the members and replied "no".

One disbelieving journalist yelled at him - "WHAT?". After all Opec is all about managing the market with quotas.

No quotas would mean a very different Opec to put it mildly.

Mr al Attiyah subsequently made it clear there are still quotas, so some of the confusion was dispelled.

Quota changes

The other confusion surrounds the fact that Opec decided to simultaneously cut production and increase production quotas.

The key to understanding this apparent contradiction is that the group's members are exceeding their production quotas.

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They always do that, but the excess now is greater than normal.

The reason is that the group was anxious to reassure the market that they would not allow shortages to develop in the event of a war in Iraq.

They produced more without making a corresponding increase in quotas.

Now, with the war related disruption less than many feared, the group think they are producing too much, hence the decision to curb production.

But they want to bring the reality and the quota - some might say the reality and the fiction - into line.

The Iraqi ghost

But some analysts think the increase in official quotas is in effect a parcelling out of Iraq's market share among the other ten members.

It is currently supplying no oil to world market, although some of its oil fields are now creaking back into action and feeding domestic supply.

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Iraq has really been the ghost at this feast. It has no oil exports and sent no delegate to the meeting.

This from a founder member that hosted the inaugural meeting in 1960, and a country that has world's second largest oil reserves.

The Opec Secretariat had sent an invitation via the Embassy in Vienna to Amer Mohammed Rasheed, the Oil Minster under Saddam Hussein.

Mr Rasheed didn't reply and certainly didn't turn up.

He is now the six of spades in the pack of cards issued to American soldiers in Iraq, depicting people that the US wants to arrest.

The last reported sighting of him put him in a refinery in Iraq surrounded by pits of burning oil.

When I called at the Iraqi Embassy I was told - over the intercom - that they were not sending a delegate and were not a functioning Embassy.

They were just waiting for a new government and instructions from Baghdad.

An uncertain future?

But when Iraq does return to the market it may well be a problem for the rest of Opec.

Will they relinquish the additional quotas as Iraq gets back to pre-war production?

And, in the longer term, Iraq could, with investment, become a much bigger producer of crude oil.

Some analysts think Iraq won't accept being constrained by an Opec quota - being so desperate for every dollar it can get to pay for reconstruction.

It is conceivable that it might even leave Opec.

If and when Iraq increases production substantially there might be a dilemma for the organisation.

If demand for oil grows weakly a resurgent Iraq could mean a declining share for the rest of the group.

The former Saudi oil minister Sheikh Zaki Yamani thinks it could even contribute to the break-up of Opec.

But then Opec has been written off before and it is still very much with us.

If demand for oil is strong then Opec might well survive even if it has to contend with an Iraq fulfilling its potential.

Opec's future will depend in part on how well the global economy performs, which will affect how much energy we want to use.