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Audio Tapes
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Listening Library (a division of Random House) released volumes 1-7 (unabridged revised texts) on audio tapes in 2002 and 2003. Volumes 1 and 5-7 were also available as abridged editions, and the entire series were available as 'audiobooks' (similar to ebooks). Volume 1 is the only tape with two major variant covers (see pictures below).

Narrated by Bill Irwin.

Volumes in the LL Audio Tape Series (click to enlarge):
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In 1985, the Cassette Book Company also released an audio version of Digest #64, Smuggler's Cove. It was narrated by Cam Clarke and is rather hard to acquire.