By Andrew Walker BBC economics correspondent

Opec ministers are having to consider opposing points of view

A small petrol station just over the canal from Opec's Vienna headquarters was doing fairly brisk business in the evening ahead of a meeting of the organisation's energy ministers.

It is a gathering overshadowed by painfully high prices for petrol and diesel fuel.

Will those officials from Opec's 11 member countries do anything to ease the financial pressure on those motorists they would see filling up if they looked out of the office window?

The Opec view, shared by industry analysts, is that there's not much they can do. But for sure, they are under some pressure.

In the UK, Chancellor of the Exchequer Gordon Brown last week said: "Opec must raise production to meet rising demand."

Claude Mandil, the head of the International Energy Agency - a kind of watchdog for the developed world - said that more Opec oil would be helpful.

Refinery problems

But most experts say the immediate problem in the industry is not the amount of crude oil being supplied, but the availability of refineries to process it, to produce the petrol, diesel fuel and other refined products consumers want.

Refinery capacity was already tight before Hurricane Katrina hit US refineries in the Gulf of Mexico coast. The weather damage made that problem more acute.

Paul Horsnell, head of energy research at the investment bank Barclays Capital says Opec is not the problem.

Supply has been able to cope with the demand. I find it surprising to say that demand is outstripping supply Adnan Shihab-Eldin, acting secretary general of Opec Opec hits back at Brown comments

He says the problem is years of underinvestment in refineries. And it is not a problem that can be fixed quickly. He says a new refinery costs at least three billion dollars. And if there was a decision to build a new one now, it wouldn't come on stream until the next decade.

If Opec were to supply more oil it would be heavy oil. That creates a specific problem for refiners.

Apart from the general shortage of refinery capacity, there are not enough with the right equipment to take heavy oil and get good yields of lighter products - notably petrol and diesel - where demand is particularly strong.

Unusual position

However, in spite of all this, Opec ministers have been discussing a proposal to increase crude oil production by half-a-million barrels a day.

But why, if crude oil is not the problem? Perhaps to defuse some of the political pressure, and perhaps to send a signal to the market that Opec will provide what's needed.

It may take months for damaged refining capacity to return to normal

The Saudi Arabian Minister Ali al Naimi captured the rather strange position Opec is in. Asked if he supported the proposed production increase he said "absolutely yes".

Is there a need for more crude oil? "Absolutely not," he said.

Other members of the group don't want an increase now. Some have said they have had difficulty selling crude oil already. So another proposal on the table is no action now, with a commitment to respond quickly with extra oil if there is a need.

Whatever the decision about crude oil output, most analysts think the prices paid by final users, including what motorists pay at the pump, are going to stay high.