Oct. 5 (Bloomberg) -- Valero Energy Corp., the largest U.S. refiner, shut unspecified units at its Port Arthur, Texas, plant for planned maintenance.

The San Antonio-based refiner said the units will be down from 7 a.m. New York time today until 7 a.m. Oct. 11, according to a report to the Texas Commission on Environmental Quality. Valero spokesman Bill Day said the maintenance will have ``no material impact on production.''

One of the units being shut is a hydrotreater, said a person familiar with the operations. Hydrotreaters reduce the sulfur content in gasoline feedstock.

The Port Arthur refinery, the largest of Valero's 17 plants, has capacity to process 325,000 barrels of oil a day.

To contact the reporter on this story: Barbara Powell in Dallas at Bpowell4@bloomberg.net.

Last Updated: October 5, 2007 12:46 EDT