The planning committee concluded in 1992 that the best solution was to add a third runway to the airport and construct a supplemental two-runway airport in one of the neighboring counties.
Members of the community opposed a third runway, as did the Highline School District and the cities of Des Moines, Burien, Federal Way, Tukwila and Normandy Park, but a 1994 study concluded there were no feasible sites for an additional airport.
In June 1951 there were four runways at 45-degree angles, between 5,000 and 6,100 feet (1,500 and 1,900 m) long; the northeast–southwest and northwest–southeast runways intersected just west of the north–south runway that eventually became today's runway 34R.
Runway 34 was lengthened to 7500 ft in 1951, to 8500 ft by 1958 and to 11900 ft by 1962. The April 1957 OAG shows 216 departures a week on United, 80 Northwest, 35 Western, 21 Trans-Canada, 20 Pan Am, 20 Pacific Northern and 10 Alaska.
It is the main hub for Alaska Airlines and its regional subsidiary Horizon Air, whose headquarters are near the airport.
It is a hub and international gateway to Asia and Europe for Delta Air Lines, which has expanded at Sea–Tac since 2011.
The Port received $1 million from the Civil Aeronautics Administration to build the airport and $100,000 from the City of Tacoma.