Brent crude headed for a sixth weekly loss, the longest losing streak since 2002, as OPEC boosted production to a 14-month high amid a global surplus. West Texas Intermediate was on track for its biggest monthly decline in more than two years.

Futures fell as much as 1.9 percent in London, bringing October's drop to about 11 percent. Both Brent and WTI are poised for their biggest monthly declines since 2012. U.S. crude production climbed to the highest level in at least three decades last week. Traders are split on whether Saudi Arabia will deepen the crude price cuts that propelled oil into a bear market this month.

"Fears of a supply glut and slow economic conditions continue to weigh on the market," said Gene McGillian, a senior analyst at Tradition Energy in Stamford, Connecticut. "The bears are in control and the market continues to come under pressure."

Brent for December settlement slid $1.37, or 1.6 percent, to $84.87 a barrel at 11 a.m. New York time on the London-based ICE Futures Europe exchange. The volume of all futures was 21 percent below the 100-day average. Prices have lost 1.5 percent this week.

WTI for December delivery declined $1.30, or 1.6 percent, to $79.82 a barrel on the New York Mercantile Exchange. Volume was 11 percent below the 100-day average. Prices are down 12 percent this month and 1.5 percent this week. Brent traded at a premium of $4.98 to WTI on ICE, compared with $5.12 at the end of last week.