US crude oil inventories climbed again last week.
The latest data from the Energy Information Administration showed that commercial crude inventories rose by 384,000 barrels in the week ending July 3.
This brought the total number of barrels in storage to 466 million barrels, still at the highest level for this time of year in about 80 years.
Last week, stockpiles rose for the first time in nine weeks, by 2.4 million barrels.
Following the data release on Wednesday morning, West Texas Intermediate crude oil slipped into the red, falling nearly 1% to around $US51.84 per barrel.
Oil prices have fallen sharply this week, as analysts recognised the extent of oversupply in the market, and the turmoil in Greece sparked a broader selloff in commodities. WTI is now near its lowest level in three-months.