economic impact study houston airport system city of bill white mayor richard m vacar director aviation airplane greater area covers 8 778 square miles fourth largest us in the ranks third number fortune 500 corporate headquarters 20 home to 5 000 energy related establishments including 11 top 25 oil and gas exploration production firms 15 nation s petroleum pipeline operators port first foreign tonnage is a diverse international business center specializing financial investment medical research treatment aerospace manufacturing cargo transportation distribution south central region united states companies are based offers more than 165 golf courses 6 100 food 62 hotel rooms 1 7 million feet convention space 45 religions one only five cities