Pre-orders for Harry Potter and the Half-Blood Prince have topped 100,000, according to bookseller Amazon.co.uk.
JK Rowling gave birth to daughter Mackenzie Jean in January
The latest instalment in JK Rowling's saga, out on 16 July, has been number one in Amazon's sales chart since its publication date was announced.
"Our customers are clearly incredibly excited about the sixth Potter book," said managing director Robin Terrell.
Just one novel remains to complete the series, which began in 1997 with Harry Potter and the Philosopher's Stone.
The fourth book in the series, Harry Potter and Order of the Phoenix, was Amazon's most popular pre-ordered item ever, with 420,000 copies pre-ordered prior to its release in June 2003.
Harry Potter and the Half-Blood Prince charts Potter's sixth year at Hogwarts School of Witchcraft and Wizardry as Lord Voldemort grows stronger.
Rowling, who gave birth to her third child in January, has already revealed that the Half-Blood Prince is neither Harry nor Voldemort.