"Shell takes all spills seriously, regardless of size and we have responded promptly to this incident," the Company press release said.
According to Shell, the size of the sea surface affected is estimated to be some 31 kms by 4.3 kms at its widest point and the sheen is currently moving west from the field.
"We have deployed a Remote-Operated Vehicle (ROV) to do inspection checks and monitor the subsea leak which is on a flow line on the sea bed," Shell said.
The Gannet field is in the Central North Sea around 112 miles (180km) east of Aberdeen. It is operated by Shell U.K. Limited on behalf of itself and Esso Exploration and Production UK Limited.