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Production totalling 500,000 barrels a day has been lost since February after attacks on oil facilities by rebel groups.

In London, North Sea Brent crude oil jumped 74 cents to an all-time high of $72.20 a barrel

A senior OPEC delegate told Reuters on Tuesday the group considered current prices too high, and they had nothing to do with the realities of supply and demand.

"OPEC believes strongly that prices are too high and nobody wants to see these prices," the delegate told Reuters. "(But) it has nothing to do with fundamentals."

$10 a barrel

Likelihood: It is unlikely but still possible that oil prices could plunge again once fears about Iran and Iraq settle down. There is more than enough oil in the world to easily meet all demand and just over six years ago oil was at this price.

Impact: Very low oil prices would bring cheap petrol and further encourage use of gas-guzzling 4x4 cars and oil for central heating. A return to cheap energy and petrol at 60p a litre could harm the environment, although it would force oil companies to cut back on further exploration.

$30 a barrel

Likelihood: It is quite possible that oil could return to this level, which was considered the norm just a few years ago. The Organisation for Petroleum Exporting Countries used this price as a target level. Many oil companies still use this level - or slightly lower - in deciding whether to proceed with any particular new development.

Impact: This level seems to nicely balance the world's need for reasonably priced energy. Oil at $30 a barrel does not raise global inflation or inhibit economic activity. Petrol prices would remain at reasonable levels.

$70 a barrel

Likelihood: It is here now but most analysts believe prices cannot stay this high. There could be spikes higher but the long-term trend should be down.

Impact: Oil companies make record profits at this level and are happy to spend more and more on exploration and production. But if prices stay this high, global economic growth will be hit, inflation will rise and users will seek alternative fuel sources. Petrol prices have already hit an average of 97p a litre, diverting consumers' cash from other spending.

$100 a barrel

Likelihood: Unlikely, although even conservative financial institutions such as Goldman Sachs have warned we could see $100 oil. A military strike on Iran could easily trigger this level, although a sudden spike would almost certainly be followed by a steep fall.

Impact: Governments would bring in taxes to dampen oil demand while industrial users would switch fuels. Inflation would rocket upwards and consumers would cut back on the rest of their domestic spending as petrol costs soared to more than ?1.30 a litre. $100 oil would boost energy efficiency and could speed a move to cleaner fuel. Gas prices tend to follow oil so renewables could be favoured over gas for electricity production.