Last week declared war on Amazon by discounting 360,000 titles 10% below Amazon’s prices. The mega-retailer, which launched with the slogan “Earth’s Largest Bookstore,” quickly responded by lowering prices on thousands of bestsellers. Overstock CEO Patrick Byrne told PW he plans to keep up the pressure on Amazon by continuing the deep discounts through midnight August 7.

For some titles, that can mean more than 55% off, much lower than most stores can purchase new books, and even lower than Amazon. Curtis Sittenfeld’s novel Sisterland, with a suggested list price of $27, is now $11.48 at Amazon and $10.33 (or 61% off) at Overstock. David Sedaris’s Let’s Explores Diabetes with Owls, which also retails at $27 is $11.97 (or 56% off) at both Amazon and Overstock.

Byrne plans to review the program weekly to determine if he will continue the deep discounting. As for Overstock’s own book category slogan, it is working to live up to it: “We Wrote the Book on Savings.”