Fans can take a deep sigh of relief in the knowledge that Prometheus will NOT be watered down to make a PG-13 Rating. There has not been any official word from the studio yet, but the evidence can be found on the advance tickets that are now available for the film.

the last time a big blockbuster like this was allowed to stay an R was The Matrix Reloaded.

Official Synopsis:
Ridley Scott, director of “Alien” and “Blade Runner,” returns to the genre he helped define. With PROMETHEUS, he creates a groundbreaking mythology, in which a team of explorers discover a clue to the origins of mankind on Earth, leading them on a thrilling journey to the darkest corners of the universe. There, they must fight a terrifying battle to save the future of the human race.

Source: Collider