At 11:55 a.m. GMT, Brent futures had dropped 48 cents, or 0.6%, to $86.63. Down 38 cents, or 0.5%, to $82.35, was the most active U.S. West Texas Intermediate contract.
In contrast to US oil prices, which were up 26 cents, or 0.31 percent, at $82.95 per barrel, Brent futures were up 10 cents, or 0.11 percent, to $87.39 a barrel.
The president of NS Trading, a division of Nissan Securities, Hiroyuki Kikukawa, has brought attention to growing worries regarding the world's oil supplies.