Oil prices dropped nearly 10% on Monday as the deteriorating world economy threatens to cut fuel consumption further.
US crude settled down $US4.61 to $US40.15 per barrel, while London Brent crude fell $US4.14 to settle at $US42.21 per barrel.
Prices previously peaked at $US147.27 per barrel on 11 July, 2008, prompting OPEC to introduce cuts totaling 4.2 million barrels per day since September.