Brent crude fell to the lowest level in almost four years after the International Energy Agency said oil demand will expand this year at the slowest pace since 2009. West Texas Intermediate slipped for the fifth time in six days.

Futures dropped as much as 3.1 percent in London and 2.1 percent in New York. Oil consumption will rise by about 650,000 barrels a day this year, 250,000 fewer than the prior estimate, the Paris-based agency said in its monthly market report. U.S. crude supplies probably grew by 2.5 million barrels last week, according to a Bloomberg survey of analysts before a report from the Energy Information Administration on Oct. 16.

Oil futures have collapsed into bear markets as shale supplies boost U.S. output to the most in almost 30 years and global demand weakens. The biggest producers in the Organization of Petroleum Exporting Countries are responding by cutting prices, sparking speculation that they will compete for market share rather than trim output. Saudi Arabia won't alter its supplies much between now and the end of the year, a person familiar with its oil policy said on Oct. 3.

"The IEA report is killing Brent," Bob Yawger, director of the futures division at Mizuho Securities USA Inc. in New York, said by phone. "This is the fourth month in a row where they've cut their demand forecast. There's tremendous downside risk for the market."

Brent for November settlement declined $2.54, or 2.9 percent, to $86.35 a barrel on the London-based ICE Futures Europe exchange at 10:24 a.m. in New York. It slipped to $86.17, the lowest intraday price since Dec. 1, 2010. The volume of all futures traded was 68 percent above the 100-day average for the time of day. Prices have decreased 22 percent this year.

WTI for November delivery dropped $1.71, or 2 percent, to $84.03 a barrel on the New York Mercantile Exchange. The contract settled at $85.74 yesterday, the lowest close since December 2012. Volume was 72 percent higher than the 100-day average. The U.S. benchmark grade traded at a $1.96 discount to Brent, down from $3.15 at yesterday's close.

The IEA reduced its estimate for demand growth this year for the fourth month in a row, meaning oil consumption will expand by about half the rate of 1.3 million barrels a day anticipated in June. The IEA cut its 2015 demand growth forecast by 100,000 barrels a day to 1.1 million. About 200,000 barrels a day less crude will be needed from OPEC this year and next than estimated previously, the agency said.