Repsol has been handed a £160,000 fine from the North Sea Transition Authority (NSTA) after flaring and venting 73 tonnes of gas without permission.
The operator had been given permission to flare from the Auk North, Halley and Fulmar fields in January 2019, however those contract expired in June 2022 and flaring continued into the following month.
It's the largest ever fine handed out by the NSTA after EnQuest were charged £150,000 last year.
Flaring - which is the process of burning off excess gas, or venting of unignited gas - had been halved in UK North Sea waters between 2018 and 2022, while operators are obligated to end all flaring and venting by 2030.
A Repsol spokesperson said: “We have accepted responsibility for unauthorised flaring and venting at our Auk North, Halley and Fulmar fields.
“We co-operated fully with the NSTA’s investigation and have taken steps to mitigate the possibility of any future breaches.”
Jane de Lozey, NSTA Director of Regulation, said: “Reducing emissions and meeting regulatory requirements is absolutely essential if industry is going to maintain its social licence to operate.
“Repsol has engaged with the NSTA to learn from its failings on this occasion and taken steps to ensure it does not happen again.
“We will continue to ensure that operators comply with regulations in the North Sea and will not hesitate to take action on the occasions that they do not. The NSTA is always ready to work with operators to ensure they remain in compliance, or bring them back into compliance.”