The NSW Environment Protection Authority (EPA) was asked to investigate after nearly 50 litres of marine fuel oil leaked from a pipe on the company's berth and into the harbour on September 1.

The oil spilled onto the northern breakwall and into the outer harbour but did not affect any public recreation areas.

EPA Illawarra branch manager Peter Bloem said yesterday that Park Petroleum staff had failed to operate a valve in the pipe correctly or to properly maintain the condition of the pipeline, contributing to the spill.

He noted both matters were direct breaches of the company's environment protection licence and required penalty.

"The EPA's action highlights [the] importance of making sure all staff carry out the correct procedures in relation to inspection, operation and maintenance at premises where oil or other bulk liquids are handled," he said.

The EPA also issued the company with a formal warning for deficiencies in their pollution incident response management plan (PIRMP), including failing to make the document publicly available.

Mr Bloem conceded the company had responded quickly to the spill, using booms to recover the oil, and had engaged in a "diligent clean-up effort", along with the EPA and the Port Kembla Port Corporation.

He said the company had complied with all the EPA's requests for information following the incident and had since commissioned a replacement pipe.

The company has also updated its PIRMP.

"There have been significant improvements in water quality in Port Kembla harbour over the years and spills of this kind are very rare," Mr Bloem said.

"We want to keep it that way."