Prices were also downbeat amid persistent concerns over the eurozone debt crisis, they added.
Brent North Sea crude for delivery in September fell 60 cents to $102.82 a barrel in late London deals.
New York's main contract, light sweet crude for September, dropped $1.22 to $87.28 a barrel.
The US Department of Energy announced that crude stockpiles rose by 2.7 million barrels last week, indicating weak demand in the world's biggest consumer of oil. Analysts had forecast a drop of 800,000 barrels.
World oil prices had rebounded Tuesday on encouraging Chinese manufacturing data. They had plunged by more than $3.50 on Monday as eurozone debt strains, centred on Spain, pointed to future weak demand for the commodity.
The oil market hit two-month highs last week as traders worried that rising tensions in the crude-rich Middle East -- particularly in Iran and Syria -- would hamper supplies.
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