Diamond Offshore Corporate Headquarters, Texas

Diamond Offshore is a major offshore drilling contractor, with 33 semisubmersible rigs, 6 jackup rigs, and 5 dynamically positioned drillships. It is one of several offshore drilling companies in this size range that are based in Houston (others include Parker Drilling, Hercules Offshore, and Rowan), all of which add to the global fleet of offshore rigs and associated drilling services. Diamond employs around 4,200 people, and was formed largely by acquisitions and consolidations of other companies, including ODECO, a Louisiana-based company that made the first large submersible drilling rig, and Zapata, a West Texas oil exploration company, whose founders include the former U.S. President, George H. W. Bush.