Oil prices widened their losses in American trade amid expectations OPEC will cut output by less than expected at its official meeting in Vienna.
As of 13:35 GMT, US crude dropped to $51.20 a barrel, while Brent declined to $59.90 a barrel.
US crude marked a 0.7% profit yesterday, the second profit in three days, while Brent climbed 0.4% as the US market shut down for an official holiday in honor of late president George H.W. Bush.
Oil fell over 5% under pressure OPEC might not cut production by as much as previously expected according to latest official statements.
Saudi energy minister said OPEC will be comfortable cutting output by only a million bpd, compared to market expectations of 1.3 to 1.4 million bpd.
OPEC's official meeting in Vienna has already started on the ministerial level today to discuss production policies and latest market developments with outside producers, Russia on top of them.
Iran Sanctions
Otherwise, as US sanctions went into effect on Iranian oil exports starting November 4, eight countries were granted waivers for 180 days, mainly China, India, South Korea, Japan, Italy, Greece, Taiwan, and Turkey, already the largest importers of Iranian oil.
Prices hit 13-month lows recently on renewed concerns over a supply glut as global producers pump record amounts of crude while global demand weakens.
Goldman Sachs expects the meeting to result in an agreement to cut output by 1.3 million bpd into 2019.