According to The New York Times marketers are looking increasingly to ad networks, which sell display advertising across groups of Web sites. Some networks offer targeted advertising; others, called vertical ad networks, include sites that focus on one subject, like travel or sports.
Imran Khan, an Internet analyst at JPMorgan Chase, estimates the top 20 ad networks earned $2 billion in 2007, or 14 percent of the $21.1 billion display market.
The reasons ad networks are thriving are price and improved technology. Ad networks charge much lower cost per thousand ads served (known as CPMs), as low as $4 on an ad network with some targeting, compared with $40 and up for some ads on premium sites like MSN or Yahoo.
