The oil industry has been accused of "marking its own homework" as new figures suggest the true number of spillages is more than double what has been reported.

Findings by marine conservation charity Oceana UK suggest levels of pollution in the North Sea have been severely underestimated due to the way in which contamination is reported.

Under drilling regulations, oil companies must report both accidental spillages and intentional discharges of what is known as 'produced water', a by-product which contains oil and other toxic chemicals and can be released into the sea under a permit.

However, if the company breaches the conditions of that permit, for example by having a higher than permitted concentration of oil in the discharge, it does not have to record this as an oil spill.

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Oceana's Sea Slick report found that if permit breaches were included with oil spills, the total volume of oil spilt into UK waters over the past 10 years increases by 43%, with more than double the volume between 2021 and 2024.

It further found that there was a 36% increase in the average concentration of oil in produced water released into UK waters between 2016 and 2020, which accounted for a 20% increase in the amount of oil released despite a fall in the overall volume of produced water.

The report estimates at least 1,331 tonnes of oil were accidentally spilled into the ocean from UK oil and gas operations between January 2011 and May 2024. A further estimated 570 tonnes were released in concentrations higher than permits allowed, taking the total amount to 1901 tonnes - enough to fill the fuel tanks of 44,000 average sized cars.

The figures are likely to be a significant underestimate, as close to a third of reported permit breaches did not include the volume of oil discharged.

The UK’s network of Marine Protected Areas have suffered 248 permit breach spills in the last three and a half years, with just under half (49%) of these breaches failing to disclose the volume of oil that was discharged. 

According to Oceana, 84% of the oil discharged in breach of permit was released by just five companies.

Over the past five years there have been just two convictions or fines, with BP fined £7,000 for violating the Offshore Petroleum Activities act in 2020 for a spill which happened in 2016.

Individual fines are capped at £50,000. BP generated an operating revenue of $210.13bn (£156.73bn) in 2023.

Since 2014, less than2% of all oil discharge permit applications have been rejected. Of the permit breaches reported between January 2011 to May 2024, less than 1% were investigated.

A request under the Freedom of Information Act revealed only 15% of oil and gas infrastructure was inspected in 2023, down from 25% in 2022. 

Hugo Tagholm, Executive Director of Oceana UK, said: “Our investigation reveals a shambles of opaque and incomplete reporting that is concealing the true scale of the toxic oil pollution causing devastation for UK seas and marine wildlife. I can’t know how a dolphin feels trying to hunt underwater with lung lesions, or a seabird that is drowning because its oiled feathers mean it cannot fly. But I do know it isn’t good enough.

"The oil industry has so far been allowed to mark its own homework on this with barely any oversight. The government can and must now chart a new course, holding the industry accountable and ensuring that our seas get the protection they deserve.” 

Commenting on the findings of Oceana’s report, Dr Rosie Williams, Postdoctoral Researcher at the ZSL’s Institute of Zoology, UK said: “A growing body of research now recognises that the steady release of oil and other toxins into marine environments poses a huge threat to marine life.

"Substances such as PAHs and heavy metals can accumulate in animals and act as carcinogens and negatively impact the immune and reproductive systems. This bioaccumulation of chemicals is also a major concern from a human health perspective, as they enter our own food system. We need the government to do more to hold oil companies to account.

"The under-reporting from the industry on what toxins are being released into our ocean is an issue that must be urgently addressed.”  

A Department for Energy Security and Net Zero spokesperson said: “We have a comprehensive framework of environmental protection measures for offshore oil and gas activities.

“Every oil spill, and discharge non-conformance is investigated by OPRED proportionately, which can take enforcement action against operators if needed, including the use of fines or referral for criminal prosecution. We review and update guidance as required.”