Global oil prices could fall as low as $20 per barrel next year, as Opec's decision to abandon a formal production quota exacerbates a bulging supply glut.

Speaking as the price of a barrel of Brent crude, the benchmark international contract, slipped 5.2 per cent to $40.75 in New York, the lowest since February 2009, Ole Hansen, head of commodity strategy at Saxo Bank, said it was "difficult to rule out anything".