LONDON (March 22): Oil prices slipped to three-month lows on Wednesday after data showed US crude inventories rising faster than expected, piling pressure on OPEC to extend output cuts beyond June.

A deal between the Organization of the Petroleum Exporting Countries and some non-OPEC producers to reduce output by 1.8 million barrels per day (bpd) in the first half of 2017 has had little impact on bulging global stockpiles of oil.

OPEC, which sources say is increasingly leaning towards extending cuts, has broadly delivered on pledged reductions so far, but non-OPEC states have yet to cut fully in line with commitments.

"OPEC has used up most of its arsenal of verbal weapons to support the market. One hundred percent compliance by all is the only tool they have left and on that account they are struggling," said Ole Hansen, head of commodity strategy at Saxo Bank.

Benchmark Brent crude was down 75 US cents at US$50.21 per barrel at 1103 GMT, after dropping to US$50.05, its lowest level since OPEC announced on Nov. 30 its plan for cuts. The deal with non-OPEC states was reached in December.

US light crude was down 68 US cents at US$47.56 a barrel, also slipping towards a three-month low.

The American Petroleum Institute said on Tuesday that US inventories climbed by 4.5 million barrels to 533.6 million last week, outpacing analyst forecasts of 2.8 million.

Investors now want to see whether Wednesday's figures from the Energy Information Administration, a unit of the US Department of Energy (DoE), confirm the rise.

"A look below US$50 (for Brent) is quite possible today if DoE data show a similar pattern, but it's impossible to say how far below US$50," Commerzbank analyst Carsten Fritsch said.

US shale oil producers have been adding rigs, pushing up the country's oil production <C-OUT-T-EIA> to about 9.1 million bpd, from around 8.5 million bpd in late 2016.

"OPEC's market intervention has not yet resulted in significant visible inventory drawdowns, and the financial markets have lost patience," US bank Jefferies said in a note.

But the bank said the market was undersupplied and, if OPEC extended cuts into the second half, inventories would draw down and prices recover above US$60 in the fourth quarter.

However, it said US crude production was expected to grow by 360,000 bpd in 2017 and 1 million bpd in 2018, and a price recovery could spur more US shale activity.