US Western Texas Intermediate (WTI) fell below $35 per barrel for the first time since February 2009 today - chased lower by the global benchmark, Brent crude, which slid below $37 per barrel for the first time since 2008.
The renewed pressure came a day after Iran vowed to ramp up production once sanctions are lifted, following the July agreement on its controversial nuclear programme. This stoked fears that the oil market will continue to be oversupplied by Opec members next year.
On Friday, the International Energy Agency (IEA) warned the global supply glut was likely to deepen next year and put more pressure on prices.
Oil prices have fallen to levels not seen since height of the global financial crisis after Opec failed to agree a production ceiling at the start of this month, which spooked investors. Analysts and traders subsequently said this was an effective abandonment of production level limits.
There's also anxiety over the potential effects of a widely expected interest rate rise from the United States' Federal Reserve at its meeting this week, the first rise in borrowing costs in nearly 10 year. It would push up borrowing costs in highly indebted emerging market countries, with uncertain consequences.