Brent crude futures were trading at $51.46 per barrel at 0645 GMT, down 35 cents, or 0.68%, from their previous close, Reuters wrote.
U.S. West Texas Intermediate (WTI) crude was down 42 cents, or 0.84%, at $49.76 per barrel.
Traders said oil markets had come under pressure after OPEC reported a rise in output, despite the producer cartel having plans, potentially with non-OPEC producer Russia, to cut production in a bid to rein in a global glut, according to the report.
"Crude responded predictably, with both Brent and WTI falling," said Jeffrey Halley of brokerage OANDA.
OPEC on Wednesday reported its oil production climbed in September to the highest in at least eight years, and raised its forecast for 2017 non-OPEC supply growth, pointing to a larger surplus next year despite the group's proposal to cut output.
The group pumped 33.39 million barrels per day (bpd) last month, up 220,000 bpd in August.
The Energy Information Administration is due to publish official storage inventory data later on Thursday, Reuters reported.
The private American Petroleum Institute reported on Wednesday that U.S. crude inventories rose by 2.7 million barrels to 470.9 million barrels in the week to October 7. This would be the first rise in oil stocks following five straight weeks of declines.
But the market received some support from China, which imported record volumes of crude oil last month, eclipsing the United States as the world's top buyer of foreign oil for the third time in a year, in a trend that could soon put the Asian nation at the top of the world's oil import table permanently.