Wikipedia
Gas-s-s-s (also known as Gas! or It Became Necessary to Destroy the World in Order to Save It) is a 1970 motion picture produced and released by American International Pictures. It was producer Roger Corman's final film for AIP, after a long association. He was unhappy because AIP made several cuts to the film without his approval, including removing the final shot where God commented on the action - a shot which Corman regarded as one of the greatest he had made in his life.
The movie is a post-apocalyptic dark comedy, about survivors of an accidental military gas leak, of an experimental agent that kills everyone on Earth over the age of twenty-five. (A cartoon title sequence shows a John Wayne-esque Army General announcing — and denouncing — the "accident"; the story picks up after the victims have died.)
The lead characters, Coel and Cilla, were 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".