The Seaway is an important crude oil transfer link between two petroleum regions within the United States.
Seeking to capitalize on the pipeline's location to gather raw natural gas in Oklahoma and Texas for transport to the company's refinery complex at Sweeny, Texas, and other refineries near Houston, Phillips converted the system to ship natural gas south instead of shipping crude oil north.
As well as for an 85 miles (137 km) lateral to the ECHO crude storage facility in southwest Houston and the Port Arthur/Beaumont refining complex.
The 40 inches (1,000 mm) Capline has been pumping offshore oil north from Louisiana to Patoka, Illinois since the 1960s.
the "Southern Leg", "Cushing MarketLink", or "Gulf Coast Pipeline Project") of the proposed Keystone XL show that it would run 435 miles (700 km) from Cushing to Nederland, Texas near Port Arthur, where it could tie into an existing 47 miles (76 km) pipeline to the Houston area.