The Texas City economy has long been based on heavy industry, particularly shipping at the Port of Texas City, as well as petroleum and petrochemical refining. The Texas City Industrial Complex is a leading center of the petrochemical industry. Within this complex, the Galveston Bay Refinery operated by Marathon is the second-largest petroleum refinery in Texas and third-largest in the United States. The Port of Texas City became the third-leading port in Texas by tonnage and ninth in the nation. In recent decades, the city's planners have made efforts to diversify the economy into tourism, health care, and many other sectors. As early as 1974, Texas City was placed on the top-ten list for the EPA superfund. Outdated practices for the disposal of toxic waste have continued there for years.