Oil fell more than $1 a barrel on Wednesday after a U.S. government report showed larger-than-expected increases in crude and gasoline stockpiles in the world's top consumer.
The U.S. Energy Information Administration said crude stocks rose by 6.9 million barrels last week, well over the 100,000 barrels forecast by analysts. Gasoline stocks were up 1.8 million barrels, almost double the market forecast.
The completely unexpected build in crude stocks is the surprise of the day. And it is very bearish, said Tim Evans, analyst at Citigroup Global Markets.
Brent crude was down 91 cents at $70.93 by 1442 GMT, having fallen as low as $70.65. U.S. crude was down 70 cents at
Oil was down earlier after a general strike in Nigeria had yet to affect oil shipments from the world's eighth biggest exporter, although the senior staff oil union PENGASSAN said it will withdraw its members from crude export terminals by midnight on Wednesday.
Oil exports have so far been undisturbed by the general strike because unions have allowed staff of the Department of Petroleum Resources, which regulates the industry, to remain at the terminals to oversee the loading of tankers.
Unions called the strike after rejecting government concessions on fuel prices as too little too late. The strike is a challenge to newly-inaugurated President Umaru Yar'Adua and comes after violence flared in the oil-producing Niger Delta over the weekend, pushing prices to a 10-month high on Monday.
The offices of Western oil companies operating in the African country were closed along with most other businesses, but its oil output and exports were uninterrupted, company officials said.
We believe that even if the strike goes on, oil supply disruptions are likely to prove minimal -- this was historically the case, said Barclays Capital.
The bank added that the strike in Nigeria highlighted market vulnerability to supply disruptions.
(Additional reporting by Neil Chatterjee in Singapore)