Lacking standards to weigh costs against safety, BP and its partners made critical errors leading to the largest offshore oil spill in U.S. history, according to a scientific panel report obtained by Reuters on Tuesday.

Interim findings from the National Academy of Engineering and the National Research Council attribute the massive spill to workers’ decisions to move ahead with temporary abandonment of BP’s doomed Macondo well despite warning signs from a key test of well integrity.

“The various failures mentioned in this report indicate the lack of a suitable approach for anticipating and managing the inherent risks, uncertainties … associated with deepwater drilling,” the report said.