In 1981, the US National Public Radio (NPR) service broadcast a six-and-a-half-hour radio dramatization of Star Wars. By comparison, the 1977 film ran two hours and one minute. Unfortunately, the program is not available from Audible.com (where I get all my paid audio content) but you can get it on CD, if you still have a CD player, from HighBridge Audio. From the blurb:
When this series was first broadcast on National Public Radio in 1981, it generated the largest response in the network’s history: 50,000 letters and phone calls in a single week, an audience of 750,000 per episode, and a subsequent 40-percent jump in NPR listenership.
This landmark production, perhaps the most ambitious radio project ever attempted, began when Star Wars creator George Lucas donated the story rights to an NPR affiliate. Writer Brian Daley adapted the film's highly visual script to the special demands and unique possibilities of radio, creating a more richly textured tale with greater emphasis on character development. Director John Madden guided a splendid cast—including Mark Hamill and Anthony Daniels, reprising their film roles as Luke Skywalker and the persnickety robot See Threepio—through an intense 10-day dialogue recording session. Then came months of painstaking work for virtuoso sound engineer Tom Voegeli, whose brilliant blending of the actors’ voices, the music, and hundreds of sound effects takes this intergalactic adventure into a realm of imagination that is beyond the reach of cinema.
Also available is a five-hour radio rendition of the Empire Strikes Back, a three-hour version of Return of the Jedi and a collector's edition of the entire trilogy. Warning: they're not cheap.
Shockingly, there appear to be no plans afoot to bring any of the prequels to radio. Presumably this is because video games dressed up as movies are rather more difficult to dramatize than actual storytelling.