More than 8,000 items are missing from libraries in West Sussex.
The latest stocktake revealed that 7,402 books, 157 audiobooks and 600 music items have disappeared from shelves.
West Sussex County Council libraries service estimates that the missing stock would cost £57,531 to replace.
Marketing and customer services manager Alan Goodman said: "The resale value of these as used library items, however, would be far less than this - in the region of £14,000."
He said some items had been stolen while others have been filed wrongly or issued incorrectly due to human error or a faulty bar code.
He said: "We cannot detect what proportion applies to each factor but we do know that these figures change each day as items are found or returned and then marked off the system so they can go back on to the correct shelf to be borrowed."
A further 4,608 items - 0.47 per cent of the total stock - have been borrowed but not returned despite three overdue reminder messages.
The list mainly consists of books but 101 DVDs, 13 videos, 98 music CDs and 17 audiobooks are also missing.
The losses are not unusual for libraries. More than 5,000 books, DVDs and CDs are stolen or not returned to libraries in Brighton and Hove each year.
In Peterborough last month a former library worker was sacked after stealing CDs worth £800 and selling them on eBay.
When the British Library moved to new headquarters on London's Euston Road in the 1990s, 8,000 books worth at least £250,000 went missing.
Top five most stolen books are said to be those by Charles Bukowski, Jim Thompson, Philip K.
Dick, William S. Burroughs and any graphic novel.
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