Brent crude futures were at $65.81 per barrel at 1222 GMT, down $0.05 from their last settlement. US West Texas Intermediate (WTI) crude oil futures were down $0.41 at $56.15 per barrel.
"Crude oil futures continue to demonstrate whippy trades as markets balance between OPEC-led cuts and the effects of rising US production levels," said Benjamin Lu, commodities analyst at Singapore-based brokerage firm Phillip Futures. Increasingly event-driven trading was adding to market volatility, he said.
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Chevron Corp and Exxon Mobil Corp released rival Permian Basin projections on Tuesday, pointing to increased shale oil production.
If realised, the increases would cement the pair as dominant players in the West Texas and New Mexico field, with one-third of Permian production potentially under their control within five years.
Data from the American Petroleum Institute (API), an industry group, also showed larger-than-expected gains in US crude stockpiles.
US crude inventories rose by 7.3 million barrels in the week ended March 1 to 451.5 million, compared with analysts' expectations for an increase of 1.2 million barrels, the API said. Crude stocks at the Cushing, Oklahoma, delivery hub rose by 1.1 million barrels.
"An increase in US crude inventories is weighing on oil prices and in the long term, concerns over rising oil production in the Permian region are keeping a lid on prices," said Kim Kwang-rae, commodity analyst at Samsung Futures in Seoul.
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Official data from the US government's Energy Information Administration was due later on Wednesday.
The rise in North American production undermines supply cuts led by the Organisation of the Petroleum Exporting Countries (OPEC).
OPEC and its allies have pledged to curb output by 1.2 million barrels per day and they are likely to push back their decision whether to extend the production agreement to June from April, sources said.
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