Wikipedia has a quick summary of the history:
The first processing units of the Port Arthur Refinery were constructed in 1902 by the Texas Company, later Texaco. The roots of this refinery can be traced to the Spindletop oil boom near Beaumont, Texas. It came into operation in 1903. Port Arthur is in eastern Texas on the Gulf of Mexico. At certain points during its lifespan it was considered the flagship refinery of Texaco.
On January 1, 1989, Saudi Refining, Inc. purchased 50% of the Port Arthur refinery (and two others) from Texaco to form a joint venture with Texaco called Star Enterprise. In 2001, Texaco was purchased by Chevron. Shortly thereafter Chevron's interest in this refinery (and two others) was sold to Shell on February 13, 2002. This new joint venture was called Motiva Enterprises LLC. Until recently, the Motiva Port Arthur Refinery was a joint venture with a 50% ownership between Shell Oil Products US and Saudi Refining Inc. Shell Oil Products is part of Royal Dutch Shell. Saudi Refining is part of Saudi Aramco. Approximately 1,200 people are employed at the site.
In March 2016, the joint venture between Shell and Saudi Aramco was set on course to dissolve, and this refinery is now controlled by Saudi Aramco effective May 1, 2017....
...Four years after Port Arthur underwent its $10 billion expansion, making the facility the biggest producer of gasoline, diesel and other petroleum products in the United States, Saudi Arabia-based Saudi Aramco is poised to become the sole owner of the facility....
...As per an agreement with Shell, Saudi Aramco will retain Motiva's name, Port Arthur refinery, and 24 distribution terminals. In Texas, Aramco will have the exclusive rights to use Shell brand for gasoline and diesel sales. In return, Shell will walk away with two Louisiana refineries (Convent and Norco), 11 distribution terminals, and a $2.2 billion balancing payment....
