As fans desperate to read the latest adventures of schoolboy wizard Harry Potter place orders for the new book due out Saturday, bookshops and other sellers are practicing some dark arts to ensure a share of the profits.

The impending release of "Harry Potter and the Half-Blood Prince," (search) J.K. Rowling's penultimate installment in the Potter chronicles, has sparked a massive price war as retailers across the United Kingdom — and to a lesser extent in the U.S. and elsewhere — try to gain crucial early market share.

While bookstores are largely relying on huge late-night launch parties — complete with sorting hat competitions offering iPods and signed books as prizes — ahead of the midnight release, supermarkets and online retailers are trying to cast their own spell.

Asda, the British supermarket chain owned by Wal-Mart Stores Inc., and its rival Tesco PLC, the country's No. 1 supermarket chain, are both offering the book for 8.96 pounds ($15.78) — a 47 percent reduction on the recommended retail price of 16.99 pounds ($29.92). Amazon.co.uk, which has set up a secure, 200,000 square foot warehouse to pack the books, is offering a similar price of 8.99 pounds ($15.83).

Retailers in the United States reported competitive prices, but no serious undercutting. Amazon.com and Barnes & Noble.com were both selling it for $17.99, 40 percent off the list price of $29.99, and Barnes & Noble was offering it at $16.19 for people in its membership program.

Wal-Mart is offering the book for $16.66 and discount warehouse club Costco put a $15.99 price tag on the book.

There is a danger that cutting prices too far could erode profits entirely — British publisher Bloomsbury has declined to disclose how much it charges retailers for each copy, but analysts suggest it would be about 55 percent of the recommended sale price.

Despite the risk of undercutting, grabbing a significant share of the sales of the new books is nothing to be sneezed at. Bloomsbury has declined to reveal how many editions are in the first print run, but retailers put projections at around 2 million to 2.5 million, given the 10.8 million being printed by U.S. publisher Scholastic.

"They'll be ready to reprint pretty quickly, in the first week or so," said Jon Howells, a spokesman for Ottakar's bookstores.

Amazon said it has more than 500,000 pre-orders in Britain alone and more than twice that worldwide, while Asda noted that the release of the previous book in the series, "Harry Potter and the Order of the Phoenix," was its fastest selling item across all its departments in 2003.

"We expect to sell three times as many copies of Harry Potter in one day as we sold of "The Da Vinci Code" — last year's bestselling book — in an entire year," said David Rutley, e-commerce director at Asda.

WHSmith said it has received half a million pre-orders, the most ever in its 210-year history. The bookseller, which is offering the book for 9.99 pounds ($17.56), is also giving away voucher booklets that give readers 75 pounds ($132) off future purchases.

Bookstore chain Waterstone's, which is offering the book for 11.99 pounds ($21.15) said it would not be drawn into a price war. Spokeswoman Lucy Avery said "at the end of the day the book is about children and we feel it's encouraging children to read."

However, Avery acknowledged that Waterstone's was sweetening the offer to prospective buyers by throwing in a free copy of "Lionboy" by Zizou Corder.

Ottakar's, which is selling pre-order copies for 10.99 pounds ($19.39), is following the same route, offering a free copy of "Bringing Up Baby Dragons," an "encyclopedia" for children on the creatures, with the first 25,000 orders.

"It's huge, this is the biggest launch of the year and will be the biggest until the next Harry Potter book," said spokesman Jon Howells.

Howells said the company, which has re-branded its 137 stores across the country "Pottakars" for the launch, had not yet decided how much it will charge for the book once selling starts on Saturday.