The price of crude oil has risen, after an Israeli attack on Syria raised fears of heightened conflict in the Middle East.
Opec's decision to cut output adds pressure for price rises
Worries that a general strike in Nigeria could also cut global production if it goes ahead later this week also contributed, as the West African country is the world's fifth biggest oil producer.
By mid-afternoon in London, Brent crude was up 25 cents a barrel at $28.96,
extending a 15%.
And in New York, light crude
oil rose 18 cents to $30.58, remaining well above the $30-per-barrel mark, a level that big oil consumers find uncomfortably high.
UN emergency talks
Oil prices have been rising for the last fortnight since Opec, the cartel of oil-producing nations, announced it would slash output by 3.5% from the beginning of November.
A tropical storm in the Gulf of Mexico has also shut down oil facilities there in recent days.
But the latest twist to tensions in the Middle East is looming large on traders' radar screens. Israel launched an air raid against Syria over the weekend, striking what it said was a training camp for suicide bombers.
Nigeria's fuel prices are a contentious issue
The United Nations is holding emergency consultations about how to respond to the attack on Syrian territory.
Trade unions in Nigeria are due to begin a general strike on Thursday in protest at the recent increase in the price of fuel which until now has been subsidised by the government.
The government's decision to cut the subsidy could lead to a 12% rise in local fuel prices.
A previous attempt to end the subsidy in June led to a 10-day strike and rioting.
The government says propping up the price of fuel is a waste of money that could be better spent on welfare and anti-poverty measures, but the trade unions view the cut as an attack on workers' living standards.
The strike is likely to have an impact on the eighth all-Africa Games which Nigeria is hosting this week.
The games are costing Nigeria an estimated $700m to host. Fifty nations are due to attend, and the government hopes to boost its images as a "big brother" to other African countries.