Although the practice is all but obsolete today, for decades radio spots were used to promote new films to American audiences. For many of us, this was an era where you felt like your social status had improved immeasurably if your latest used car had the ability to pick up FM radio stations, even if the vehicle could be relied upon to break down several times a week. Radio spots generally ran in a variety of lengths ranging from 60 seconds to 10 seconds. Because they lacked visual elements, the producers of the tracks often used sensationalistic tactics to gain the attention of listeners, often stressing the most comedic or shocking elements of the film depending upon its subject matter. As with all things nostalgic, there is a passionate interest in radio spots among some retro movie fans who collect the vinyl discs. Most were released on 45 RPM but in earlier versions from the 1950s, they were usually on 33 1/3" records.
Here is an original 1973 radio spot for William Friedkin's "The Exorcist".