Paul J. Heald has self-archived “The Demand for Out-of-Print Works and Their (Un)Availability in Alternative Markets.”
Here's an excerpt:
Prior studies demonstrate the shocking unavailability of most books published in the 20th Century, prompting The Atlantic Monthly headline: How Copyright Made Mid-Century Books Vanish. The unavailability of new editions of older works would be less problematic, however, if little consumer demand existed for those works. In addition, the lack of new editions would be much less troubling if the works were easily available in alternative forms or markets. Newly collected data provides evidence of the demand for out-of-print books and then charts the availability of out-of-print works in digital form (eBooks and .mp3), in used book stores, and in public libraries. The situation with books remains dismal, although music publishers on iTunes seem to be doing a much better job of digitizing older works and making them available than do book publishers. Some theories for this discrepancy are offered.