In New York, the US benchmark West Texas Intermediate (WTI) for September delivery slid 29 cents to USD 97.88 a barrel.
Brent crude for September was down USD 1.18 cents at USD 104.81 in London trade.
Prices were nearly 10 per cent off their highs of late June, and back to where they stood at the beginning of May.
"The last couple of days showed that we continue to shed some of the speculation in the market that was built into what pushed us to nine month highs," said Gene McGillian of Tradition Energy.