Production at the UK's North Sea Buzzard oilfield has fallen slightly after a technical glitch, three trading sources said on Thursday.
One source said that output was down by about 20,000 barrels per day (bpd) as of Thursday morning, while another said the outage was up to 30,000 bpd.
The field's operator Nexen did not immediately respond to a request for comment.
Buzzard produces about 180,000 barrels per day (bpd) and is the largest contributor to the
Forties crude oil stream, one of four grades of oil that underpin the dated Brent benchmark.
The partial outage contributed to a narrowing of the front-month Brent futures spread on Thursday to 28 cents a barrel.
(Reporting by Julia Payne and Alex Lawler; Editing by Alexander Smith)