What factors are causing this unremitting increase and what are the likely consequences for consumers and the global economy?

What is causing the latest price spike?

This was triggered by concerns about violence in Nigeria and Algeria as well as the delay of the elections in Pakistan.

Prices have remained above $70 a barrel for most of the year

The assassination of the former Pakistani Prime Minister Benazir Bhutto increased oil prices because stability in Pakistan is important to US policy in the Middle East.

Threats to oil workers and facilities in Nigeria have cast a long-term shadow over oil supplies from the world's eighth largest oil exporter.

Suspected militant attacks on Wednesday in Nigeria's main oil city, Port Harcourt, heightened concern over the potential for further disruptions in shipments.

"With the military and the militant warlords engaged in a violent tit-for-tat, the risk for oil disruptions in Nigeria remains higher than in the past few months," said Olivier Jakob of Petromatrix.

The weak dollar, which makes it cheaper for importers to buy dollar-denominated oil supplies, is also a major factor.

Is demand for oil continuing to soar?

Yes. The biggest catalyst for oil's seemingly remorseless rise has been the simplest economic driver there is: the balance between demand and supply.

Demand is at an all-time high, fuelled by the continued breakneck economic expansion of the Indian and Chinese economies.

With more than a billion people in each country, and both economies growing fast, manufacturers and consumers are sucking in energy at an ever-increasing rate.

China's booming economy is sucking in a huge amount of oil

China overtook Japan as the world's second-largest consumer of oil in 2003 and is closing in on the US, with demand for oil growing at about 15% a year.

Analysts worry global demand for oil is so intense that supplies may not keep pace.

Demand will rise by an average of 2.2 million barrels a day next year, the International Energy Agency says, compared with the 1.5 million-barrel rise seen in 2007.

It says annual demand will rise 2% up to 2012, while other projections suggest demand could soar from about 90 million barrels a day to as much as 140 million over 25 years.

What is Opec doing about the situation?

As the leading oil supplier in the world, producers' cartel Opec is under constant pressure to do something about the price bubble.

It recently bowed to pressure to pump more oil, agreeing to raise its production quotas by 500,000 barrels a day from 1 November.

Reports suggest the move was forced through by Saudi Arabia and that few other Opec members either have much stomach for increasing output or much capacity to spare.

Opec has said the market is "very well supplied" with crude and will continue to be so in the immediate future.

It has blamed speculation by market traders - who can make money by betting on the future direction of prices - for the continuing price rises.

Critics of Opec say it must act more aggressively to bring prices down.

"The response from Opec has been pretty poor so far," says John Roberts, an energy security analyst with commodities research firm Platt's.

"The sentiment in the market is that it is time for Opec to increase production again."

Who are the winners and losers from costly oil?

Taking inflation into account, prices are still below levels seen in late 1980, when a barrel of oil - in today's prices - was worth more than $101.

Back then, costly oil helped contribute to a recession in the US and similar fears are resurfacing now.

The Bush administration has said it is "very concerned" about current price levels, at a time when the economy is already expected to slow significantly next year.

High energy prices make life more expensive for consumers and businesses, having an knock-on effect on their spending in other areas.

Gasoline prices are hovering not far below the $3-a-gallon mark in the US, while UK petrol retailers have warned prices could soon rise above £1 a litre.

But on the other side of the fence, oil giants such as ExxonMobil and BP are having a wonderful time, while oil-rich countries are also smiling.

Oil wealth has underpinned President Hugo Chavez's efforts to reshape Venezuela, allowing him to fund extensive social programmes and reject US criticism of his policies.

Russia's oil and gas bonanza has underwritten efforts by President Vladimir Putin to exert state control over the country's energy sector.

Where will prices head next?

Many people scoffed when analysts from investment bank Goldman Sachs said in 2005 that prices could eventually top $100 a barrel.

"All of the factors that pushed us above $80 are now moving us higher," said Peter Beutel at Cameron Hanover in Connecticut.