BP workers were preparing to vacuum up about 4200 gallons or 100 barrels of crude oil and a smaller amount of produced water that overflowed from a tank at a Prudhoe Bay oilfield facility, the Alaska Department of Environmental Conservation said on Tuesday.
The spill occurred Monday afternoon from a flow station tank on the east side of the giant oilfield.
The DEC said the cause of the overflow was a failure of instrumentation and valves that are supposed to control tank volume.
BP has been monitoring air quality at the site, and will use vacuum truck to suck up the spilled crude when conditions are deemed safe to do that, the department said.
A BP Alaska spokesman told Reuters that production from the oilfield was unaffected by the incident, with no injuries or environmental damage.
Both state officials and BP said all of the overflowed oil and produced water was caught in a secondary containment that surrounds the tank.
While officials have an estimate of the volume of released material, an exact figure was unavailable on Tuesday, partly because snow in the secondary containment had mixed with the oil and produced water, the department said.