Barnes & Noble.com has expanded its relationship with America Online Inc’s AOL to the tune of $40m over the next four years. The book retailing giant’s online subsidiary has signed a contract with AOL Networks that will make it the exclusive bookseller on the 10 million-member proprietary online service. The two had a previous agreement that made Barnes & Noble the exclusive bookseller on the AOL Marketplace area of AOL.com. The deal gives Barnes & Noble extensive placement throughout most of AOL’s service, including links from the various channels to Barnes & Noble titles in that particular area of interest. But the most appealing feature of the deal for Barnes & Noble is that it shuts the door on the competition, as other online booksellers – such as Amazon.com – will be prohibited from advertising on the proprietary AOL service for the term of the arrangement. Amazon.com, however, remains the exclusive bookseller on AOL’s web site (AOL.com) and its AOL NetFind search engine.