Just in case anybody wondered, the lyrics are in the Digital Tradition here (click).
Here's what Merle Travis said about the song (quoted in Sing Your Heart Out, Country Boy, by Dorothy Horstman):

I had to do an album at Capitol Records, and Cliffie Stone said, "Do a folksong album." I said, "Well, Burl Ives has sung all the folksongs," and he said, "Write some." So that's how I came to write 'Sixteen Tons' - because I had to. There was an old saying around the coal mines in the Depression days. Somebody'd say, "how you doing?" And he'd say, "Well, all right, I guess. I can't afford to die, because I owe my soul to the company store." I just wrote around that.

I'd sure like to see lyrics to "21 Tons." Somebody got 'em?
-Joe Offer-