US oil prices fell for a six straight day today, approaching 12-year lows hit last month, weighed by brimming crude inventories and a Goldman Sachs forecast that prices would remain low and volatile until the second half of the year.

Market intelligence firm Genscape reported the Cushing, Oklahoma delivery hub for US crude futures saw a build of almost 425,000 barrels in the week to 9 February.

Crude inventories in Cushing hit all-time highs just shy of 65 million barrels during the week ended 5 February, government data showed today.

US crude was down 60 cents, or 2%, at $26.85 per barrel by 5.23pm Irish time.

Earlier, it fell to within 3 cents of the $26.19 intraday low hit in January, then its weakest price since 2003.

Traders scrambled to buy bearish US crude options, particularly for $25 puts, on the back of the continuous price slide. Technical analysts said the $25 level could be hit in a matter of days.

The spread between the first two months in US crude widened nearly 60 cents to as much as $2.80. That was the largest discount, or "contango," between the two contracts since November, indicating tight storage space was limiting interest to buy prompt barrels to store and sell at a later date.

"If storage becomes any scarcer, producers will have no choice but to sell it (the front-month) even lower," said Pete Donovan, broker at New York's Liquidity Energy.

Brent was down 55 cents, or 1.8 percent, at $30.29 per barrel.

Investment bank Goldman Sachs said in a note to its clients it expected oil prices to fluctuate between $20 and $40, with significant volatility and no trend until the second half.

Oil has fallen almost 75% since mid-2014 as competing producers pumped 1-2 million barrels of crude daily exceeding demand, just as China's economy hit lowest growth in a generation. 

Brent gained briefly after a report cited by sources that some OPEC countries were trying to achieve a consensus among the group and key non-members for an oil production "freeze". 

Despite that, fighting among OPEC members for market share appeared to heighten as Iran offered its crude to Asia at a discount to rival OPEC producer Saudi Arabia.

"There's a price fight within OPEC for Asian market share, and there are worries that storage capacity is going to be breached," said Bjarne Schieldrop, chief commodity analyst at SEB in Oslo.