The price of oil, one of 2005's biggest stories, is forcing its way back into the headlines as a political row with Iran threatens to interrupt supplies.
By Ben Richardson
BBC News business reporter
Crude oil prices have rallied in recent weeks as concerns over Iran's nuclear ambitions have escalated.
Iran has been threatened with referral to the United Nations for restarting its nuclear programme, and there are fears that sanctions may be imposed.
As this unfolds, problems with Nigerian supply have also pushed prices higher.
On Friday, a barrel of benchmark light crude rose 0.6% to $64.72 in New York. Brent crude, London's main traded oil, was 0.9% higher at $63.18.
While that is well below the record of $70.85 a barrel set in August 2005, analysts are revisiting their estimates for average prices this year.
Many had expected oil prices to continue to drop, falling to the mid-$50 range, as supply caught up with demand and economic growth slowed in some of the thirstiest users.
The concern now is that uncertainty in the market will buoy prices above $60.
"Expectations, perceptions often affect the price more than physical changes," said Dr Manouchehr Takin, a senior petroleum analyst at London's Centre for Global Energy Studies.
However, there is no doubt that Iran is going to loom large over the oil market and should the situation deteriorate to the point of sanctions then speculative buying would increase.
Taking Iran's oil output off the world market would be a "major blow", Dr Takin said.
High oil prices have weighed on world growth and driven inflation
"Prices would shoot up," he said. "But how high they will shoot up is anybody's guess."
Last year analysts warned that oil could break the $100 a barrel mark, and while that still is the case, it all depends on the size of the external market shock.
Iran is second largest producer of crude in oil-cartel Opec behind Saudi Arabia, and accounts for almost 4 million barrels a day, about 5% of the world's total output.
There is not enough spare capacity to cover a shortfall, especially as worldwide oil stores have been depleted due to strong demand in previous years and a failure to increase refining output.
Senior officials from the UK, US, Germany, France, Russia and China will meet in London on Monday to discuss the conflict with Iran.
The UK, Germany and France have called for Iran to be referred to the UN's Security Council, but said that talk of sanctions is premature.
Nigeria has often had problems with kidnappings and oil supply
Iran wants to continue negotiations over its nuclear programme, which it claims is for nothing more than peaceful power generation.
In the short-term, problems in Nigeria are likely to have a more immediate effect on the market, analysts said.
Oil firm Royal Dutch Shell has had to cut its output from Nigeria by 20% after a pipeline explosion and the kidnapping of four foreign oil workers.
It said it is losing 226,000 barrels a day after shutting its EA platform in the southern Delta region and closing the pipeline feeding an export terminal.
Dr Takin said that problems in Nigeria are nothing new and the market is used to both kidnappings and disruption to supplies.
However, Iran is a "different story", he said.