Oil eased on Friday after a volatile previous session when the market grappled with supply worries in Nigeria, the world's eighth-largest producer, and a firmer US dollar. US crude oil was off 13 cents at $136.61 a barrel by 0740 GMT, but still within sight of last week's record $139.12.
The contract traded in a near-$6 range on Thursday, ending 36 cents higher at $136.74 a barrel, as concerns mounted about a possible strike in Africa's top oil producer. July Brent crude, which expires later in the day, was down 59 cents at $135.50 a barrel. Nigeria's senior oil workers' union, which was pushing for the expatriate managing director of Chevron's local unit to be transferred out of the country, said on Thursday that talks to avert a lockout were not going well and renewed its strike threat.
"Certainly, we're worried about Nigeria, we're still very mindful of the situation," said Peter McGuire, managing director of Commodity Warrants Australia.
A strike would further dent oil output in Nigeria, where a fifth of capacity has been shut since early 2006, when ethnic militants in the Niger Delta began a violent campaign of sabotage against oil installations. But US currency gains weighed on oil prices, which have gained more than 40 percent this year as investors played on a weaker dollar and bought commodities to hedge against inflation.