Brent North Sea crude for May delivery fell as low as USD 103.95 in afternoon London deals. It later stood at USD 104.51 per barrel, down USD 1.11 from Tuesday.
New York's West Texas Intermediate (WTI) for May dipped 22 cents to $99.52 a barrel.
CMC Markets analyst Jasper Lawler said falling prices were "likely as a result of reduced geopolitical tensions" between Ukraine and Russia.
Investors are continuing to monitor the tense situation in Ukraine, as NATO said yesterday it had suspended all cooperation with Russia and questioned Moscow's claim to have withdrawn troops along the Ukraine border.
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Russian troops are massed near the Ukrainian border, sparking fears about Moscow's plans following its takeover of the Crimean peninsula last month.
Meanwhile, the US government's Energy Information Administration (EIA) revealed that American crude inventories slid 2.4 million barrels in the week to March 28.
That confounded market expectations for a gain of 700,000 barrels and indicated stronger-than-expected demand.
The market also set aside data showing a pick-up in US job creation in the private sector in March.
Payrolls firm ADP said US businesses added 191,000 jobs in March, below the 215,000 projected by analysts but an improvement on the 178,000 in February.
The oil market had already fallen sharply yesterday, as poor global manufacturing data sparked serious worries about the outlook for world energy demand.