Pennzoil is an oil company founded in Oil City, Pennsylvania. In 1963, South Penn Oil merged with Zapata Petroleum to become Pennzoil. During the 1970s, the company moved its offices to Houston, Texas. It was then headquartered in Pennzoil Place, a recognizable skyscraper designed by the architect Philip Johnson. In 1998, the company merged with onetime rival Quaker State to form Pennzoil-Quaker State. In 2002, the Royal Dutch/Shell Group purchased Pennzoil-Quaker State to form SOPUS--Shell Oil Products US.