Oil slid below $45 a barrel for the first time since OPEC agreed to cut output in November as US shale confounds the producer group's attempts to prop up prices.
Oil prices sharply extended losses just before Tuesday's settlement, with USA crude breaking below $48 a barrel for the first time in more than a month.
Both benchmarks lost 4.9 percent Thursday, falling to their lowest level since November 30 - the day when OPEC members and Russian Federation agreed to cut their individual oil production to increase prices.
Both contracts slid during the session to the lowest since November 30, the day OPEC agreed to cut supply.
30 to cut its output by 1.8 million barrels per day for the first six months of the year, a move that led to a 25 percent gain in oil prices.
Meanwhile, stocks of crude oil and products in the USA have remained at high levels.
Meanwhile, Opec members' crude output was unchanged in April at 31.85m barrels per day, according to an S&P Global Platts survey released today.
Gains in oil futures were capped as concerns over rising US oil output persisted, after oilfield services firm Baker Hughes reported its weekly USA rig count rose by 6 to 703.More news: Love game for Serena: Spox says Williams is pregnant
Gasoline futures fell 3.2% to $1.4851 a gallon, trading at a three-month low. The global benchmark crude traded at a premium of US$2.57 to July West Texas Intermediate.
There was also a sign of slowing energy demand in China, the world's second largest oil consumer, when a survey showed growth in that country's services sector in April was at its slowest in nearly a year.
Oil prices have gained support but stockpiles are still high and production from non-participating countries such as the United States has been rising, keeping crude below the $60 level that OPEC kingpin Saudi Arabia would like to see.
USA crude stockpiles fell less than expected last week, while gasoline inventories grew as demand remained weak, the Energy Information Administration said on Wednesday, keeping concerns about global supply on a simmer.
The Saudi OPEC governor was speaking by telephone from Vienna where he is attending a meeting of OPEC's governing board along with his counterparts from the 13-country OPEC - which accounts for a third of global oil production. The U.S. oil rig count has more than doubled from a year go to 703 this week, according to Baker Hughes Inc. data.
"A lot of global players didn't expect USA production to be able to ramp up this quickly, at this price level", said Jenna Delaney, senior oil analyst at Platts Analytics.
"We disagree and think that OPEC will manage to extend the cuts and we'll see inventories fall in the second half of the year".
USA production "continues to grow hand over fist, and the market will remain well oversupplied given the lack of" refined fuel demand, he added.