This week, WTI broke through $60 a barrel for the first time since June 2015, while Brent breached $67 for the first time since May 2015.
Expectations of robust oil demand growth and high OPEC and allies' commitment to the production cuts have prompted analysts to raise again their forecast for oil prices in 2018, and they now see WTI averaging $55.78 per barrel next year. The spread between the benchmarks widened throughout the year, as Brent responded to the drawdown in supply from major world producers while US output continued to grow.
Trading was typically thin at the end of the year, with many traders still on holidays.
US West Texas Intermediate (WTI) crude futures slipped 13 cents to $59.51 a barrel this evening, a day after briefly touching $60 a barrel.
The U.S. Energy Department said crude stocks fell 4.6 million barrels in the latest week. Inventories excluding the nation's strategic reserve have declined more than 11% in the a year ago. Brent crude futures LCOc1 were last up 45 cents at $66.62 a barrel at 1932 GMT.
A Reuters monthly poll showed analysts expect Brent crude to stay close to $60 in 2018.More news: Massive Lottery Ticket Win Sold in Mississauga
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Libya's oil production was last put by officials at around one million bpd but exact figures are hard to obtain a country riven by factional conflict.
China's imports at around 8.5 million bpd, already the world's biggest, are expected to hit another record in 2018 as new refining capacity is brought online and Beijing allows more independent refiners to import crude.
In global markets, China has issued crude oil import quotas totalling 121.32 million tonnes for 44 companies in its first batch of allowances for 2018.
An explosion has rocked a crude oil pipeline that feeds the Es Sider sea terminal in Libya, an oil source in the country said.
Both pipelines are expected to return to normal operations by early January.