An American oil corporation has been fined £7000 over a North Sea diesel spill.

As much as 25.7 tonnes of oil leaked into the water from the Judy Riser platform in December 2013.

The spill began when a temporary fix meant to solve a problem with a wrongly fitted valve failed and allowed oil to pump freely into a tank and overflow.

ConocoPhillips pleaded guilty to releasing oil into the sea at Aberdeen Sheriff Court on Tuesday.

Fiscal depute Richard Brown said: "When the volume of fluid reached a high level in the hazardous open drains tank, this activated an alarm in the control room.

"The first alarm in the hazardous open drains tank initiated at 11.40pm on December 16.

"Control room operators who were dealing with the shutdown acknowledged the alarms but did not take any follow up action as they believed that the drains system had not yet been commissioned and therefore was not their responsibility.

"The diesel then overflowed from that tank to the hazardous drains caisson. The caisson then began to fill with diesel eventually overflowing resulting in diesel being released into the North Sea.

"Had the alarms been responded to, a pump in the drains tank or the caisson could have been activated manually and the fluid would have been redirected back into the system."

Environmental experts said the leak would not have any significant impact on the environment as the diesel would disperse over time.

Sheriff Morag McLaughlin said she had taken into account the fact that ConocoPhillips had pleaded guilty at the earliest opportunity and had never been convicted of a crime before.