The PSA said the release occurred Sept. 12. There were no reports of injury or major infrastructure damage but an investigation was launched given the severity of the incident.
A spokeswoman for the PSA told United Press International via email that BP is the operator at the Ula field.
"We cannot confirm any amount at this point in the investigation but the leak is substantial," she added.
The agency said production at the Ula field was suspended, the production facility in question was shut down and all personnel were evacuated to a drilling platform.
BP had no comment available about the incident. The company said it started production "an important phase" of development at the Ula field in April that would enhance production for 10-20 years.
The Ula field came on stream in 1986. It was expected then to have a life expectancy of 11 years.
"The leak arose in the separator module on Ula's production platform," the PSA stated. "Nobody was in the module when the incident occurred."