U.S. crude oil futures settled at their lowest level in four years on Thursday after data showed crude stocks built up at a key U.S. delivery point last week.
Brent crude also fell to a four-year low and was last below $79 a barrel on concerns that China will see further economic slowdown and as Saudi Arabia kept silent about a possible cut in production.
China's economy lost momentum in October, with factory growth dipping and investment growth hitting a near 13-year low, reinforcing expectations of a slower increase in fuel demand.
Developing economies had been a major support for oil over the past decade, but demand is now failing to keep up with increasing supply from North American shale production.
U.S. light crude settled $2.97 lower at $74.21 per barrel, it lowest close since Sept. 2010.
Brent crude for December was last down about $2 at $78 a barrel after falling to an intraday low of $77.99, its lowest since 2010.