S
- Samoa Air (American Samoa, 1987 to 2003)
- Saturn Airways (1960 - 76, to Trans International Airlines)
- Seaboard World Airlines (1946 - 80, to Flying Tiger Line)
- Shawnee Airlines (1968 - 1977)
- Shuttle by United and United Shuttle (1994 - 2001)
- Sky Trek International Air Lines (1996 - 2000)
- Skybus Airlines (2007 - 2008, ceased operations 5 Apr 2008)
- SkyTrain Airlines (to Air Great Lakes)
- SkyValue (2006 - 2007)
- Skyway Airlines
- Slick Airways (1946 - 1965, to Airlift International)
- SMB Sedalia Marshal Booneville
- Song (2003 - 2006, Merged back in with its parent company, Delta Air Lines)
- South Pacific Island Airways (SPIA) (American Samoa, ceased operations in 1987)
- Southeast Airlines (1992 - 2004)
- Southern Air Transport (1929 & 1947 - 1998, to Southern Air)
- Southern Airways (1943 - 1979, to Republic Airlines)
- Southern Jersey Airways
- Southwest Airways (1941 - 1958; renamed Pacific Air Lines in March 1958)
- Standard Air Lines (1926 - 30) 1927 subsidiary of Aero Corp. of Ca., In 1930, bought by Western Air Express, thru merger with TAT became TWA, Transcontinental & Western Air, Trans World Airlines
- Standard Airlines (1947 - 1949) non-scheduled airline ordered to cease operations for violations after fatal crash
- Standard Airways (1960s)
- StatesWest Airlines (1986 - 1993)
- Stol Air Commuter (1974 - 1979, renamed WestAir Airlines)
- Sunbird Airlines (1979 - 1987 to CCAir)
- SunCoast Airlines (? - 1988)
- Sun West Airlines (c. 1980 - c. 1985)
- Sunworld International Airlines (? - 2004)
- Sunworld International Airways (1983 - 1988)
- Superior Airlines (1993 - 1995 to Mesa Airlines
- Swift Aire Lines (1969 - 1981, merged with Golden Gate Airlines)
Read more about this topic: List Of Defunct Airlines Of The United States