Paramount Pictures is releasing Grease in a sing-a-long format for a limited two-week engagement this July.

The new edition is set keep the No.1 musical of all time on top.

"It's exciting. I don't know if the second one that's high up is Mamma Mia. I don't know where that stands with Grease right now but that certainly is a big one. It's great. Why wouldn't it be? It's really fun to have that [legacy]," the film's director Randal Kleiser said.

Proud of this new achievement, Mr Kleiser also tried to explain how his movie has lasted so long.

"I think the chemistry of the cast is certainly part of it," he said. "The infectiousness of the fun that everybody had when we were making it. The music is really infectious too. I think people love the music and the themes of high school are things people respond to. So I think it's just a mixture of all those things but mostly it's the music and John and Olivia are the things that grab people."

The fact that it reached to all ages is another factor.

"It's funny because everywhere I go in the world, this reaction occurs, people loving the movie from little kids to grandmas, all the way through young adults and teenagers. It's kind of like a perfect storm of elements that just came together," said the director.

Grease Sing-A-Long opens in selected theatres in Los Angeles and other major US cities in July 8.