According to Vanity Fair, other actresses in consideration included Susan Dey from “The Partridge Family,” and Barbara Raffin from “The Sentinel” and “God Told Me To.” It seemed important to the casting agents that their Sandy be able to sing.
“Grease” was not Olivia Newton-John’s first movie. By 1978, she had already starred in an Australian musical film called “Funny Things Happen Down Under,” and a near-forgotten sci-fi musical called “Toomorow.” Neither of those films were notable hits, however, and producer Allan Carr was reluctant to give her another chance. Additionally, Newton-John wasn’t currently keen on making more movies as her music career was doing fine. In her words: “I was very anxious about making another film, because my music career was going well, and I did not want to mess it up by doing another movie that wasn’t good.” Even Producer Randal Kleiser was unconvinced as to her ability to play Sandy, feeling that she wouldn’t be able to provide the appropriate level of lasciviousness.
It was Travolta who insisted on Newton-John. He loved her singing voice, and knew that she was a major musical superstar.
“She had a brilliant voice, and I didn’t think there could be any more correct person for Sandy in the universe. [Casting her would be like] putting Taylor Swift in that role today. … I never let up on it. I insisted that she be met and that we cast her.”
Travolta seemed to have the right instincts, as Newton-John’s star only rose as a result of “Grease.”