The 2005 Cadillac STS is available as a 4-door, 5-seat sedan. Starting at $40,525, the 2005 Cadillac STS V6 is powered by a 3.6L, 6-cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 24-mpg on the highway. The top of the line 2005 Cadillac STS V8, priced at $47,025, is powered by a 4.6L, 8-cylinder engine mated to an automatic transmission that returns an EPA estimated 17-mpg in the city and 26-mpg on the highway.