ExxonMobil's Baytown Refinery is the second largest oil refinery in the United States located in Baytown, Texas. It has capacity of 584,000 barrels per day (92,800 m3/d). The site first opened in 1919 and was originally operated by the Humble Oil Company. Today, it is the largest employer in the city. The plant takes up 2,400 acres (9.7 km2) of land next to the Houston Ship Channel.
In 1988 and 1989, the plant expanded operations without notifying the U.S. federal government as required under the Clean Air Act's New Source Review provision. This went unnoticed by the Environmental Protection Agency until 2000.