An investigation into the September incident by the Petroleum Safety Authority found BP was in serious breach of Norwegian regulations.
"The PSA has concluded that the incident had the potential to become a major accident, with the risk that a number of lives might have been lost and substantial material damage caused," the agency stated.
The incident led to a minor release of oil and gas but no injuries were reported. Production was shut down for more than two months as a result of the accident.
The PSA said the release came after bolts failed on a valve at the offshore installation.
The Norwegian regulator said it issued BP with a corrective order calling on the company to review its management system for offshore Norway by September.
"The PSA's investigation of the Ula incident shows that deficiencies still exist in the maintenance system," the regulator said.