Robert Ryan's incessant complaints about not receiving top billing so annoyed director Sam Peckinpah that he decided to "punish" Ryan. In the opening credits, after freezing the screen on closeups of William Holden's and Ernest Borgnine's faces while listing them, Peckinpah froze the scene on several horses' rear ends as Ryan was listed.
In an interview, Ben Johnson said that the Mexican women who "frolicked" with him and Warren Oates in the huge wine vats weren't actresses but prostitutes from a nearby brothel, who were hired by Sam Peckinpah so he could tell people that Warner Bros. paid for hookers for his cast.
According to editor Lou Lombardo the original release print contains some 3,643 editorial cuts, more than any other Technicolor film ever processed. Some of these cuts are near subliminal, consisting of three or four frames, making them almost imperceptible to the naked eye.
Sam Peckinpah stated that one of his goals for this movie was to give the audience "some idea of what it is to be gunned down". A memorable incident occurred, to that end, as Peckinpah's crew were consulting him on the "gunfire" effects to be used in the film. Not satisfied with the results from the squibs his crew had brought for him, Peckinpah became exasperated; he finally hollered: "That's not what I want! That's not what I want!" He then grabbed a real revolver and fired it into a nearby wall. The gun empty, Peckinpah barked at his stunned crew: "THAT'S the effect I want!!" He also had the gunfire sound effects changed for the film. Before, all gunshots in Warner Brothers movies sounded identical, regardless of the type of weapon being fired. Peckinpah insisted on each different type of firearm having its own specific sound effect when fired.
The train robbery itself was not in the script. All scenes were improvised on the spot, the same day. Same thing with "the walk" for the bunch to help "Angel".