West Texas Intermediate futures for September delivery is currently at $49.26 (+0.14%). On Wednesday prices reached their lowest level since April. Brent crude slid to $56.07 (-0.11%).

Data by the U.S. Energy Information Administration showed Wednesday that commercial crude-oil stockpiles unexpectedly rose by 2.5 million barrels to 463.9 million barrels. Gasoline stockpiles fell by 1.7 million barrels. Distillate stocks, which include heating oil and diesel fuel, rose by 200,000 barrels.

However, some analysts noted that demand grew significantly in the first half of the year and the World Bank raised its 2015 forecast for crude prices to $57 per barrel from $53. At the same time large inventories and rising output from OPEC members are likely to keep prices weak in the medium-term.