Oil prices fell Thursday ahead of the release of a closely watched report that is forecast to show a surge in US stockpiles to 33-year high, adding to a global supply glut.

US benchmark West Texas Intermediate fell $1.46 to $50.68 while Brent eased 98 cents to $69.55.

oil rig in Tioga, North Dakota, USA:

The weekly report by the Energy Information Administration (EIA) is expected to show supplies increased by three million barrels to 420.9 million in the week to through February 13, according to a survey by Bloomberg News.

The figure from the EIA — part of the Department of Energy — would mark the highest in weekly records since August 1982, Bloomberg said.

Ken Hasegawa, energy desk manager at Newedge brokerage in Japan, said the expected jump in stockpiles was “having negative impact on the market” and added that “the declining trend will continue in Asia”.

Last week’s report showed that US crude inventories already reached their highest levels on record for this time of the year.

Crude prices lost about 60 percent of their value to about $40 between June and late January owing to an oversupply in world markets, a weak global economy and a strong dollar.

And while they have been climbing in recent weeks on news that the number of US oil rigs in operation has fallen and energy giants are cutting back on investment, markets-watchers say volatility is likely to continue for some time.