BP said that oil production at its Prudhoe Bay oilfield in Alaska has been cut by 90,000 barrels per day (bpd) for several days due to a technical fault.
A company spokesman said output at the biggest oilfield in the United States had been reduced to 110,000 bpd after a natural gas compressor failed.
"We anticipate that fixing the compressor will require several days," said BP spokesman Daren Beaudo.
Prudhoe Bay had previously been pumping about 200,000 bpd, around half its normal output, after serious corrosion in a pipeline led BP to shut down the eastern half of the field earlier this month.
The spokesman said no one was hurt and no oil was spilled in the latest incident, which has added to worries over an oil market strained by reduced Nigerian supply and fearful of potential disruptions in the Middle East.
Oil prices rose on the news as dealers feared it would further squeeze US West Coast refiners, who have bought extra supplies from around the world this month to cover for the lost Alaskan supply, a staple of their crude diet.
US crude was up 20 cents at $71.96 a barrel, near the day's high, while Brent crude traded up 28 cents to $72.30 a barrel early this morning.