Gas-s-s-s (on-screen title: Gas! -Or- It Became Necessary to Destroy the World in Order to Save It.) is a 1970 post-apocalyptic black comedy film produced and released by American International Pictures.

It was Roger Corman's final film for AIP as director, after a long association (although he would subsequently produce a few more films for the studio). He was unhappy because AIP made several cuts to the film without his approval, including the removal of the final shot in which God comments on the action — a shot Corman regarded as one of the greatest he had made in his life.

The film is a post-apocalyptic dark comedy, about survivors of an accidental military gas leak involving an experimental agent that kills everyone on Earth over the age of 25 (a cartoon title sequence shows a John Wayne-esque Army General announcing — and denouncing — the "accident"; the story picks up as the last of the victims are dying with social commentary on Medicare and Medicaid). The subtitle alludes to the 1968 quote "it became necessary to destroy the town to save it" attributed to a U.S. Army officer after the Battle of Bến Tre in Vietnam.

The lead characters, Coel and Cilla, are played by Robert Corff and Elaine Giftos, and the cast features Ben Vereen, Cindy Williams, Bud Cort and Talia Shire (credited as "Tally Coppola") in early roles. Country Joe McDonald makes an appearance, as spokesman "AM Radio".