Premcor was a Fortune 500

Fortune 500

The Fortune 500 is an annual list compiled and published by Fortune magazine that ranks the top 500 U.S. closely held and public corporations as ranked by their gross revenue after adjustments made by Fortune to exclude the impact of excise taxes companies collect. The list includes publicly and...

 oil refinery

Oil refinery

An oil refinery or petroleum refinery is an industrial process plant where crude oil is processed and refined into more useful petroleum products, such as gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas...

 group based in Greenwich, Connecticut

Greenwich, Connecticut

Greenwich is a town in Fairfield County, Connecticut, United States. As of the 2010 census, the town had a total population of 61,171. It is home to many hedge funds and other financial service companies. Greenwich is the southernmost and westernmost municipality in Connecticut and is 38+ minutes ...

. It operated five refineries, which are located in Port Arthur, Texas

Port Arthur, Texas

-Demographics:As of the 2000 census, there were 57,755 people, 21,839 households, and 14,675 families residing in the city. The population density was 696.5 people per square mile . There were 24,713 housing units at an average density of 298.0 per square mile...

; Memphis, Tennessee

Memphis, Tennessee

Memphis is a city in the southwestern corner of the U.S. state of Tennessee, and the county seat of Shelby County. The city is located on the 4th Chickasaw Bluff, south of the confluence of the Wolf and Mississippi rivers....

; Lima, Ohio

Lima, Ohio

Lima is a city in and the county seat of Allen County, Ohio, United States. The municipality is located in northwestern Ohio along Interstate 75 approximately north of Dayton and south-southwest of Toledo....

; Hartford, Illinois

Hartford, Illinois

Hartford is a village in Madison County, Illinois, near the mouth of the Missouri River. The population was 1,545 at the 2000 census. Lewis and Clark spent the winter of 1803-1804 here, near what has been designated the Lewis and Clark State Historic Site....

; and Delaware City, Delaware

Delaware City, Delaware

Delaware City is a city in New Castle County, Delaware, United States. The population was 1,695 at the 2010 census. It is a small port town on the eastern terminus of the Chesapeake and Delaware Canal and is the location of the ferry to Fort Delaware on Pea Patch Island.-Geography:Delaware City is...

 with a combined crude oil volume processing capacity of approximately 768120 oilbbl/d (July, 2007).

Premcor was acquired by Valero in 2005. Valero would later sell the Lima facility to Husky Energy in July 2007 and close the Delaware City refinery in November 2009.

Environmental record

Researchers at the University of Massachusetts Amherst

University of Massachusetts Amherst

The University of Massachusetts Amherst is a public research and land-grant university in Amherst, Massachusetts, United States and the flagship of the University of Massachusetts system...

 previously identified Premcor as the 39th-largest corporate producer of air pollution

Air pollution

Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment, into the atmosphere....

 in the United States, with roughly 1 million pounds of toxic chemicals released annually into the air.
Major pollutants indicated by the study included sulfuric acid

Sulfuric acid

Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

 and chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

.