A spokesman says a fire at BP's Cherry Point refinery might have been caused by a leaky flange connection.
However, BP spokesman Scott Dean said Monday the information filed with the Coast Guard's National Response Center is very preliminary and the cause remains under investigation.
It remains unclear how long the refinery would be out of service as a result of the fire on Friday. The company is trying to supply customers from existing stocks or other sources.
The refinery can process 230,000 barrels of crude oil a day. It produces 20 percent of Washington's gasoline and the majority of aviation fuel for the Vancouver, British Columbia, Sea-Tac and Portland airports.
The dramatic blaze created towering flames and a thick plume of black smoke that was visible for miles.