While making this film, Sam Peckinpah's alcoholism was so advanced that he would have to start the day with a large tumbler of vodka to stop shaking. He would be drinking grenadine by mid-afternoon. After that, he was too drunk to work. James Coburn recalled that Peckinpah was only coherent for four hours a day.
Al Pacino told a German interviewer in 2014 that he was offered the role of Billy the Kid, but it didn't work out because he couldn't ride a horse. He was also wary of Sam Peckinpah's hard-living reputation.
Although Kris Kristofferson was widely felt to be too old to play Billy the Kid, it should be noted that James Coburn was much older than Pat Garrett.
James Coburn was 44 at the time of filming, although Pat Garrett was 30 to 31 during the events shown.
Kris Kristofferson and Sam Peckinpah had several heated arguments while making the film, and others on the set often thought they would fight physically. Peckinpah, always very confrontational, wanted to fight Kristofferson, but said he feared Kristofferson, a former Army Airborne Ranger, would "kill him". Kristofferson answered, "Yeah, Sam, I think you're right". In spite of this, Peckinpah referred to Kristofferson as a "fucking great guy" and said that working with him was "one of the greatest experiences of my life".