Transocean, the world's largest offshore drilling contractor based in Vernier, Switzerland, and Occidental Petroleum Parker Drilling are tenants of Four Greenway Plaza which opened in 1975; while the headquarters of Boardwalk Pipeline Partners and Humana Mitsui Oil Exploration is located in Nine Greenway Plaza.
Transocean Ltd. is the world's largest offshore drilling contractor based on revenue and is based in Vernier, Switzerland. Four Greenway Plaza 1975 Transocean
Occidental Petroleum
Parker Drilling Nine Greenway Plaza Boardwalk Pipeline Partners (HQ)
Humana
Mitsui Oil Exploration (HQ) 
