Port Arthur is considered the crown jewel of the US refinery system. The Gulf Coast facility can process 600,000 barrels of oil per day, making it the largest refinery in North America, CNNMoney reported.
Aramco previously owned 50 per cent of Port Arthur through a joint venture co-owned with Royal Dutch Shell (RDSA) called Motiva Enterprises.
In addition to Port Arthur, Aramco is acquiring full ownership of 24 distribution terminals.
Aramco also gets the exclusive right to sell Shell-branded gasoline and diesel in Georgia, North Carolina, South Carolina, Virginia, Maryland, the eastern half of Texas and the majority of Florida.
Saudi Arabia is already America's second-largest source of crude, behind only Canada. The US imported 1.3 million barrels of Saudi crude a day in February, up 32 per cent from last year, according to the Energy Information Administration.