Brent crude has slipped under the $70 mark for the first time since April.
After hitting four-year highs at the beginning of October, the global benchmark has now fallen more than 18%.
US oil is at $60.42, down more than a fifth since early October, officially putting it in “bear-market” territory.
“There is no slowing down the bear train,” said Stephen Brennock at London brokerage PVM Oil.
“Instead, the energy complex has extended a rout driven by swelling global supplies and a softening demand outlook. There is now a sense of inevitability that the European crude benchmark is poised to revisit the $60s per barrel.”