U.S. light crude (CLc1: Quote, Profile, Research) gained 49 cents to $49.37 a barrel, a whisker away from August's all-time peak of $49.40.

Concerns over Nigeria, OPEC's number five producer, compounded worries about supplies from Russia, Saudi Arabia and Iraq.

"All these factors create apprehension in the market and reinforce the view that we're on a knife's edge in terms of supply and demand," said Daniel Hynes, industry analyst at ANZ Bank in Melbourne.

"The uncertainties heighten the risk premium applied to this market. Another move to test the $49.40 could well happen this week."

Global supplies are straining to meet the fastest growth in oil demand in 24 years. World crude output is close to its limits with only top exporter Saudi Arabia holding any significant spare capacity.

In Nigeria, rebels seeking political reforms in the impoverished oil-producing Niger delta scored a success with the closure by Royal Dutch/Shell (RD.AS: Quote, Profile, Research) (SHEL.L: Quote, Profile, Research) of a small 30,000 barrels a day.

Shell evacuated some staff as a security precaution as government troops battle militia, threatening deliveries from the country that pumps 2.5 million barrels daily.

The rebels said at the weekend they would bid to extend their uprising across the West African producer's entire southern delta oil region.

Separately, Nigeria already has been forced to cut back output from surge capacity to protect its aging facilities in the first sign that efforts by OPEC countries to quell prices by squeezing out extra output may not be sustainable.

Presidential Adviser on Petroleum Edmund Daukoru told Reuters that production was reduced 10 percent to base capacity of 2.25 million bpd in August. Nigeria had been pumping at surge capacity of up to 2.55 million bpd.

Uncertainty over supplies from YUKOS (YUKO.RTS: Quote, Profile, Research) (YUKO.MM: Quote, Profile, Research) , Russia's top exporter, also is supporting prices. YUKOS last week trimmed deliveries to China.

In Saudi Arabia, clashes between security forces and suspected al Qaeda followers served as a reminder of the threat to stability in the world's biggest producer.

In Iraq, insurgents fired mortar bombs at the oil ministry building on Saturday, causing minor damage but no injuries.

But Iraqi oil exports, temporarily at least, are as high as they have been since last year's U.S.-led invasion.

Iraqi pipelines have been the target of frequent sabotage attacks. But yesterday deliveries resumed at about 450,000 bpd through the main northern line to Turkey after engineers completed repairs from a bomb attack Sept 2. Southern exports were near full capacity at two million bpd.

Extra crude from OPEC, now pumping at a 25-year high, has failed to make any impact. The group produced 30.5 million bpd in September, the highest since 1979, tanker-tracking consultancyPetrologistics said.

OPEC president Purnomo Yusgiantoro said the cartel was supplying enough crude and was not to blame for high prices. "This is because of Hurricane Ivan and some problems in other places," said Purnomo of high prices. "This is not a supply and demand problem. OPEC supply is enough," he told reporters in Jakarta.