Campaigners have slammed the "shambles of opaque and incomplete reporting" that is hiding the true scale of toxic oil pollution in the UK's seas.
Oil companies must report both accidental oil spills and intentional discharges of so-called "produced water" - a byproduct containing oil and other toxic chemicals - which can be released under permit.
But breaches of these permits have typically been excluded from external analysis and scrutiny, marine conservation charity Oceana has warned.
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."
When "permit breaches" are added to "accidental spills", the total volume of oil spilt into UK waters since 2014 increases by 43%, and more than doubles the volume between 2021-2024.
The UK's network of marine protected areas, which are home to internationally important ocean life, suffered 248 spills from permit breaches between January 2021 and May 2024, the charity found.
Oceana said enforcement of oil companies "remains inadequate" with only two recorded convictions or fines in the last five years, one of which was just £7,000.
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."
