Equinor said yesterday that it halted loading operations on the Statfjord field after oil was spotted on the surface of the North Sea.
The Norwegian energy major said the issue came to light this morning while oil was being loaded onto a shuttle tanker.
Equinor said it had taken steps to map the extent of the leak.
The Norwegian share of the field lies in blocks 33/9 and 33/12 in production licence 037, while the UK part is in block 211/25 in licences 104 and 293.
The field was developed with the Statfjord A, B and C production platforms.
Equinor said earlier this month that it would shut down down the Statfjord A platform, 43 years after it produced first oil, but that the other two installations would remain on stream until at least 2025.
Statfjord oil production is loaded into shuttle tankers on the field and shipped to a number of ports in north-western Europe.
The Norwegian share of gas from the field is piped to the Karsto processing complex north of Stavanger and on to continental Europe.
Britain’s 14.53% of the gas travels by pipeline via the Brent field to Scotland.