Publishers have been whispering about it for months, and the most recent Media Metrix numbers confirm it: the biggest bookseller on the Internet after Amazon is not BN.com—it's eBay subsidiary Half.com.

Half.com has half as many unique visitors per month as Amazon—some 9,650,000 visitors compared to Amazon's 18,910,000. The online marketplace was an early competitor to Amazon's zShops (renamed Marketplace) and has since attracted more than 15 million listings of various items. Unlike eBay itself, Half.com sells books at fixed prices. According to Kristin Keys, Half.com spokesperson, books are "a big part of the business," though she declined to break out figures for books.

Online used book sales have grown more competitive in the past year, following Amazon's absorption of Bibliofind.com and development of the "blue-box specials," which alert shoppers to the availability of a used book on the same page offering a new book for sale. The lack of used books on the BN.com site may be one of the reasons the company is falling further behind Amazon, and now Half, in traffic.

Last month, Half.com announced that the Canadian online used book dealer network, Abebooks.com, which aggregates titles from 8,400 booksellers, will begin offering titles for sale through Half.com. The company already lists titles on BN.com, though the titles appear only under the "out-of-print" tab. Judy Kam, director of marketing and business development, told PW, "They approached us about a year ago, but first they had to get their house in order after being acquired by eBay, and we had to make sure that our systems were compatible. When they came back to us this year, we could see they did a lot of things right when they set up the company and, by now, their traffic numbers are huge."

In a recent presentation to investment analysts, Amazon claimed that adding used books on its site has, paradoxically, driven sales of new books, and will continue to. The used "blue box specials" cost the company little more than Web real estate: Amazon does not have the overhead expenses of stocking and shipping and is awarded 99 cents plus 15% of the price each time an item sells. It's the ultimate online consignment gig, which has not been overlooked by eBay and Half.com, in many ways the innovators of the online used book business. By aggressively going after some of Abebooks.com's 29 million book listings, Half.com may have assured its current position as the #2 online bookseller.

With B&N behind it and Amazon ahead, Half looks like a solid second—at least until the next online bookselling shoe drops.