High Quality Content by WIKIPEDIA articles! The economy of Houston is primarily based on the energy industry (particularly oil), however, biomedical research and aerospace are a large sectors of the city`s economy. The Houston–Sugar Land–Baytown area Gross Metropolitan Product (GMP) in 2005 was $308.7 billion, up 5.4 percent from 2004 in constant dollars. The Houston metropolitan area comprises the largest petrochemical manufacturing area in the world, including for synthetic rubber, insecticides, and fertilizers. The area is the world`s leading center for building oilfield equipment. The city is home to more than 3,000 energy-related establishments, including many of the top oil and gas exploration and production firms and petroleum pipeline operators. As of 2011 23 companies on the Fortune 500 list have their headquarters in Houston or the surrounding metropolitan region.