"Classical Gas" is an instrumental musical piece composed and originally performed by American guitarist Mason Williams with instrumental backing by members of the Wrecking Crew. Originally released in 1968 on the album The Mason Williams Phonograph Record, it has been rerecorded and rereleased numerous times since by Williams. One later version served as the title track of a 1987 album by Williams and the band Mannheim Steamroller.

Williams was the head writer for The Smothers Brothers Comedy Hour at the time of the piece's release and premiered the composition on the show. Williams performed it several times over several episodes.