International benchmark Brent crude oil futures LCOc1 were trading down 7 cents at $48.98 per barrel at 0413 GMT, having closed down 1.8%, Reuters reported.
U.S. West Texas Intermediate (WTI) crude futures were at $46.74 a barrel, down 3 cents, after dropping 2.8% on Wednesday.
Traders said price falls this week had truncated a rally that pushed crude up by more than 20% earlier in August on talk of a potential deal by oil producers to freeze output in an effort to rein in oversupply.
Hopes of a deal were dampened by record output from the Organization of the Petroleum Exporting Countries (OPEC) and little prospect of voluntary restrictions.
With output high, not just from OPEC but also other top producers like Russia, and the demand outlook shaky, analysts said there was little prospect of an end to the glut, which has pulled down crude prices from over $100 a barrel to their current sub-$50 levels since 2014.
Analysts said that high storage levels pointed to an ongoing supply overhang that was weighing on markets.
Read alsoUkraine sees decline in gas, crude oil production since start of yearIn the United States, commercial crude oil stocks rose by 2.5 million barrels to 523.6 million barrels.
In refined products, stocks around the world are also brimming as demand slows while refinery output remains high.