Oil jumped more than a dollar to top $71 a barrel on Friday on fears a strike by Nigerian unions could intensify and disrupt shipments from the world's eighth-largest exporter.
London Brent crude, currently seen as the best benchmark of world oil prices, climbed $1.15 to $71.37 a barrel by 1729 GMT. U.S. light crude rose 65 cents at $69.30.
Union leaders in Nigeria vowed to extend their strike against a rise in fuel prices to a third day on Friday, after talks with the government ended in a stalemate.
Uncertainty around the course of events in the country, where a general strike is underway, continues to keep markets nervous, Barclays Capital said in a research note.
The strike has so far not stopped exports of Nigeria's gasoline-rich crude, but the government said it would no longer tolerate street blockades and intimidation by unionists, setting the stage for a more hostile face-off. Militant attacks on oil infrastructure have already cut about a quarter of Nigerian output.
The majority of oil workers have complied with the strike directive but Western multinationals have sustained production and exports by replacing union staff with management.
The market has pulled back from a 10-month high on Monday, losing nearly $2 in a three-day slide, pressured mid-week by an unexpected jump in U.S. crude stockpiles that lifted inventories to a nine-year high on abundant imports and low refinery use.
This bolstered OPEC's case that supply is healthy and tight gasoline stocks are due to a lack of refining capacity.
There is a lot of oil on the market, the stocks are very high, OPEC Secretary-General Abdullah al-Badri said on Thursday. If we add more oil, it would not go to the refineries -- it would go to the stocks.
U.S. gasoline stocks rose last week but remained more than five percent below last year amid peak summer demand, as refineries have been hit by a series of outages.
Refiners are also struggling to build up inventories of heating oil, which declined last week to be 38 percent below their levels at this time last year.
Analysts said worries over Iran's nuclear dispute, the Gulf of Mexico hurricane season and flat non-OPEC supply against a backdrop of growing demand are also supporting prices.
(Reporting by Matthew Robinson in New York, Randy Fabi in London and Neil Chatterjee in Singapore)