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The selling in crude oil accelerated in afternoon US trading, with the US and international benchmarks both down 4 per cent on the day, and trading at levels last seen in November.
West Texas Intermediate fell 4.4 per cent to $45.74 a barrel, while Brent declined 4.2 per cent to $48.68 a barrel.
Worries have been building over high North American supplies, with shale companies drilling more rapidly after oil stablised at around the $50 a barrel range this year.
US energy stocks also faced heavier losses at mid-day, with the S&P 500 sector recently down 2.3 per cent.