Production notes

Michael Crichton had become nationally famous with his best selling novel, The Andromeda Strain, which had been turned into a 1971 movie. Crichton made his debut as director with the television film, Pursuit (1972), based on one of his novels, and wanted to direct a feature. He did not want to necessarily make a science fiction film but "That's the only way I could get the studio to let me direct. People think I'm good at it I guess." Crichton's agent introduced him to producer Paul N. Lazarus III; they became friends and decided to make a film together. The script for Westworld was written in August 1972. Lazarus asked Crichton why he did not tell the story as a novel; Crichton said he felt the story was visual and would not really work as a book. The script was offered to all the major studios. They all turned down the project except for Metro-Goldwyn-Mayer, then under head of production Dan Melnick and president James T. Aubrey. Crichton said

MGM had a bad reputation among filmmakers; in recent years, directors as diverse as Robert Altman, Blake Edwards, Stanley Kubrick, Fred Zinneman and Sam Peckinpah had complained bitterly about their treatment there. There were too many stories of unreasonable pressure, arbitrary script changes, inadequate post production, and cavalier recutting of the final film. Nobody who had a choice made a picture at Metro, but then we didn't have a choice. Dan Melnick ... assured [us] ... that we would not be subjected to the usual MGM treatment. In large part, he made good on that promise. Crichton said pre-production was difficult. MGM demanded script changes up to the first day of shooting and the leads were not signed until 48 hours before shooting began. Crichton said he had no control over casting and MGM originally would only make the film for under a million dollars but later increased this amount by $250,000. Crichton said that $250,000 of the budget was paid to the cast, $400,000 to the crew, and the remainder on everything else (including $75,000 for sets).

The film was shot in 30 days. To save time, Crichton tried to shoot only what was needed, with minimal takes. Westworld was filmed in several locations, including the Mojave Desert, the gardens of the Harold Lloyd Estate, several MGM sound stages and on the MGM backlot, one of the final films to be shot there before the backlot was sold to real estate developers and demolished. It was filmed with Panavision anamorphic lenses by Gene Polito. Richard Benjamin later said he loved making the film:

It probably was the only way I was ever going to get into a Western, and certainly into a science-fiction Western.... So you get to do stuff that's like you're 12 years old. All of the reasons you went to the movies in the first place. You're out there firing a six-shooter, riding a horse, being chased by a gunman, and all of that. It's the best! The Gunslinger's appearance is based on Chris Adams, Brynner's character from The Magnificent Seven. The two characters' costumes are nearly identical. According to Lazarus, Yul Brynner agreed to play the role for only $75,000 ($403,000 in modern dollars), because he needed the money. Crichton later wrote that "most of the situations in the film are cliches; they are incidents out of hundreds of old movies", so the scenes "should be shot as clichés. This dictated a conventional treatment in the choice of lenses and the staging". The original script and original ending of the movie culminated in a fight between Martin and the Gunslinger, which resulted in the Gunslinger being torn apart by a rack. Crichton said he "had liked the idea of a complex machine being destroyed by a simple machine" but when attempting it, "it seemed stagey and foolish", so the idea was dropped. He also wanted to open the film with shots of a hovercraft traveling over the desert but was unable to get the effect he wanted within a limited budget, so this was dropped as well.

The score for Westworld was composed by American composer Fred Karlin. It combines ersatz western scoring, source cues, and electronic music.

In the published screenplay, Crichton explained how he re-edited the first cut of the movie because he was depressed by how long and boring it was. Scenes that were deleted from the rough cut include a bank robbery and sales room sequences, an opening with a hovercraft flying above the desert, additional and longer dialogue scenes, more scenes with robots attacking and killing guests including a scene where one guest is tied down to a rack and is killed when his arms are pulled out, a longer chase scene with the Gunslinger chasing Peter and one where the Gunslinger cleans his face with water after Peter throws acid on him. Crichton's assembly cut featured a different ending that included a fight between the Gunslinger and Peter and an alternate death scene in which the Gunslinger was killed on a rack. Once the film was completed on time, MGM authorized the shooting of some extra footage. A television commercial to open the film was added; because there was a writers' strike in Hollywood at the time, this was written by Steven Frankfurt, a New York advertising executive.

Westworld was the first feature film to use digital image processing. Crichton originally went to the Jet Propulsion Laboratory in Pasadena but after learning that two minutes of animation would take nine months and cost $200,000, he contacted John Whitney Sr., who in turn recommended his son John Whitney Jr. The latter went to Information International, Inc., where they could work at night and complete the animation faster and cheaper. Whitney Jr. digitally processed motion picture photography at Information International, Inc. to appear pixelized to portray the Gunslinger android's point of view. The approximately 2 minutes and 31 seconds' worth of cinegraphic block portraiture was accomplished by color-separating (three basic color separations plus black mask) each frame of source 70 mm film images, scanning each of these elements to convert into rectangular blocks, then adding basic color according to the tone values developed. The resulting coarse pixel matrix was output back to film. The process was covered in the American Cinematographer article "Behind the scenes of Westworld" and in a 2013 New Yorker online article.

The film was released on an experimental regional saturation basis and grossed $2 million in its first week in 275 theatres in the Chicago, Detroit and Cleveland areas. It earned $4 million in rentals in the US and Canada by the end of 1973. After a re-release in 1976, it earned $7,365,000.

Crichton's original screenplay was released as a mass-market paperback in conjunction with the film.

Variety described the film as excellent, saying that it "combines solid entertainment, chilling topicality, and superbly intelligent serio-comic story values". Vincent Canby of the New York Times wrote that Crichton had made "a creditable debut as a film director", but "Crichton the director seems to have had more fun with the film than Crichton the writer, whose screenplay can offer us no better explanation for the sudden, bloody robot rebellion than an epidemic of 'central mechanism psychosis.'" Gene Siskel gave the film three stars out of four, calling the first half "exciting and provocative" but thinking much less of the second half which he thought deteriorated into an "illogical and meandering chase story. It is difficult to believe the same man wrote both halves of the film." Kevin Thomas of the Los Angeles Times called it "a clever sci-fi fantasy ... with enough ingenuity and conviction to make it a successful diversion for those seeking novel rather than sophisticated entertainment." Jean M. White of the Washington Post wrote that "Crichton spends too much time establishing his robot world and short-circuits suspense with long, arid stretches of Grade B Western." The film has a rating of 83% "Fresh" on Rotten Tomatoes based on 46 reviews. The site's consensus states: "Yul Brynner gives a memorable performance as a robotic cowboy in this amusing sci-fi/western hybrid." Reviewing the DVD release in September 2008, The Daily Telegraph reviewer Philip Horne described the film as a "richly suggestive, bleakly terrifying fable—and Brynner's performance is chillingly pitch-perfect." American Film Institute lists

AFI's 100 Years...100 Thrills – Nominated AFI's 100 Years...100 Heroes & Villains: Robot Gunslinger – Nominated Villain AFI's 10 Top 10 – Nominated Science Fiction Film After making the film, Crichton took a year off. "I was intensely fatigued by Westworld", he said later. "I was pleased but intimidated by the audience reaction. ... The laughs are in the wrong places. There was extreme tension where I hadn't planned it. I felt the reaction, and maybe the picture, was out of control." He believed that the film had been misunderstood as warning of the dangers of technology: "Everyone remembers the scene in Westworld where Yul Brynner is a robot that runs amok. But there is a very specific scene where people discuss whether or not to shut down the resort. I think the movie was as much about that decision as anything. They just didn't really think it was really going to happen." His real intention was to warn against corporate greed. For him the picture marked the end of "about five years of science fiction/monster pictures for me". He took a break from the genre and wrote The Great Train Robbery. Crichton did not make a film for another five years. He did try, and had one set up "but I insisted on a certain way of doing it and as a result it was never made."

Crichton used similar plot elements—a high-tech amusement park running amok and a central control paralyzed by a power failure—in his bestselling novel Jurassic Park. Westworld contains a reference to a computer virus, one of the earliest mentions of them in fiction. The analogy is made by the Chief Supervisor in a staff meeting where the spread of malfunctions across the park is discussed.