Britain's biggest and most important oil pipeline, Forties, was ramping up throughput after repairs and was currently pumping at around half its normal rates, a trading source familiar with the operations said on Wednesday.
Forties normally pumps about 450,000 barrels per day.
The pipeline's operator Ineos restarted the pipeline earlier in the week and has pledged to resume full flows in early January. On Wednesday, Ineos could not immediately comment on the current flow rates.
The closure of the pipeline since Dec. 11 has helped push oil prices above $67 a barrel in recent weeks, their highest level since mid-2015.
Forties plays an important role in the global market as it is the biggest of the five North Sea crude streams underpinning Brent, a benchmark for oil trading in
Europe, the Middle East,
Africa and Asia.
The system, which also carries a third of Britain's total offshore natural gas output, was shut down after a crack was found.
Ineos was forced to declare force majeure on deliveries of
Forties crude oil, natural gas and condensate, suspending its contractual obligations to customers by citing circumstances beyond its control.
This is believed to be the first force majeure on a major North Sea production stream in decades. Ineos didn't say when it expected to lift the force majeure.
Ineos, a privately-owned chemicals company based in Switzerland, bought the pipeline system from BP in late October.
Reporting by Alex Lawler