The commission is investigating most of the plants for excessive releases of chemicals into the air above the town of 58,000 residents about 90 miles east of Houston.
In addition to fines of as much as $10,000 a day, the companies could face millions of dollars in costs to upgrade their refineries or chemical plants in order to prevent future problems.
Shell Oil Co. and affiliated companies are undertaking a $400-million project to clean refineries in Port Arthur and other states. Atofina Petrochemical is spending $7 million on one piece of equipment at its Port Arthur refinery, according to Reuters.
The plants being investigated are owned by Premcor Inc, ChevronTexaco Corp., BASF Corp. and Atofina, a subsidiary of France's TotalFinaElf.
A study released in November by a Rockefeller Fund organization found 4.2 million pounds of unpermitted pollutants have been released by the plants in Port Arthur so far this year.
The study paid for by the Rockefeller fund and done by the Environmental Integrity Project found that just this year there has been nearly one release a week in Port Arthur due to an "unavoidable" event.