Works by best-selliing authors are among the most popular 'missing' titles
Library books worth £600,000 have gone missing in Wales over the last two years, according to figures obtained by a Plaid Cymru assembly member.
Chris Franks found more than 100,000 books had been stolen or not returned, with losses for Wales' biggest council, Cardiff, running at £1,000 a week.
He said he is "staggered" and wants action, including a books amnesty.
Cardiff Council said it hopes a new system will combat thefts but there was "no evidence" amnesties worked.
Mr Franks wrote to all local authorities to ask for figures from their library services.
Some councils also revealed those authors whose books were most popular with thieves, or which were borrowed and not returned.
Not surprisingly, perhaps, they tallied with best-sellers such as Harry Potter author JK Rowling, Roald Dahl, Terry Pratchett and Jacqueline Wilson.
As Wales' largest local authority Cardiff, suffered the worst losses during 2006-07 and 2007-08, losing 17,160 books, worth £136,000 - more than £1,000 a week.
The city library service also collected more than £150,000 in fines on items returned late.
MISSING LIBRARY BOOKS
Bridgend - 2,529
Caerphilly - 5,719
Cardiff - 9,762
Carmarthenshire - 300
Ceredigion - no numbers, est cost £10-£15,000
Conwy - 3,177
Denbighshire - 1,437
Flintshire - 1.833
Gwynedd - 2,145
Neath Port Talbot - 1,881
Newport - 3,005
Powys - 3,053
Rhondda Cynon Taf - 9,828
Swansea - 10,427
Torfaen 6,591 (inc 2006-2007 figure)
Wrexham - 1,644
Numbers of missing library books for 16 councils in 2007-2008. Figures obtained by Chris Franks AM
At Cardiff Council, which has £73,177 worth of books missing for the last year, a spokesperson said: "The library services primary function is to lend items and it is a difficult balancing act to remain true to that philosophy with the need to control stock.
"There are two elements to this problem - those individuals who steal directly from libraries and those who have books issued and fail to return them.
"Over the years we have tried many different methods of controlling stock by way of financial penalties with some success. It is hoped that the new RFID [radio frequency identification and embedded micro-chip] system that is currently being installed in libraries will help in respect of those individuals who who steal directly.
"There is no evidence at all that amnesties work and in fact the last one we had in Cardiff only resulted in items being returned that were in poor condition or near the end of their shelf life".
Information about the book will be contained on microchips embedded within tags which are then "read" using radio frequency technology. The RFID tags last longer than barcodes - a minimum of 100,000 transactions - because nothing comes into contact with them.
In Wrexham, 74 health books were not returned in 2006-07 and another 68 copies are "missing" for 2007-08.
Forty one copies of books by children's author Jacqueline Wilson were stolen or not returned over the same period.
Mr Franks, who is to write to culture minister Alun Ffred Jones, said: "The losses incurred by libraries across Wales are frankly staggering.
"I'm appalled that borrowers are either stealing or not returning books but I also believe that all local authorities urgently need to look at their systems and ways of reducing thefts," said the South Wales Central AM.
"These thefts are a huge drain on the public purse, particularly at a time when money is tight. This is money which could otherwise perhaps be used to improve facilities for library users such as greater internet access.
"I believe that all local authorities should look at a books amnesty allowing users to return books without paying hefty fines."
He also expressed concern that several councils did not have information about the extent of thefts.