BP's internal inquiry into the Deepwater Horizon disaster concluded that the company holds some responsibility for the Gulf of Mexico oil spill.
The energy giant, however, also found that some other companies should be blamed.
It said that Swiss-based Transocean was responsible for crucial safety equipment designed to seal the well as soon as the leak began.
Halliburton, the US company that attached the wellhead to the sea floor, was also criticised for "weaknesses in cement design and testing".
The enquiry was the first in a string of investigations seeking to find out what went wrong and who is to blame.
Al Jazeera's Jonah Hull reports from London.