Oil prices have dropped further due to reports of a massive increase in US stocks that triggered growing concerns that Saudi Arabia and Russia’s efforts may not be enough to end the global oversupply. 

Brent crude fell by 15 cents from the last close to $51.5 a barrel, while the US light crude declined by 26 cents and traded at $48.40, reported Reuters.

In its report, the American Petroleum Institute (API) showed that US crude stocks increased by 882,000 barrels in the week ending 12 May to reach 523.4 million. 

Official data on US crude stocks will be released later by Energy Information Administration. 

"The number of tankers storing oil is on the rise across offshore China, as facilities on land remain full."

Both the oil benchmarks previously witnessed a steep rise in prices after Saudi Arabia and Russia agreed to extend the ongoing supply cuts until the end of March 2018. 

The Organization of the Petroleum Exporting Countries (OPEC) along with some other producers, including Russia decided to reduce oil output by 1.8 million barrels per day for the first six months of this year. 

The North Sea oil production is also expected to increase by a net 400,000bpd in the next two years as operators look to improve efficiency, which fuels oversupply concerns.  

The news agency also reported that the number of tankers storing oil is also on the rise across offshore China, as facilities on land remain full.