Advertising.com now reaches 26.9m unique users - almost 90% of the UK's internet population - according to figures from comScore Media Metrix.
Advertising.com, which is owned by AOL, has been the largest UK network for some time, and also holds the number one position in the US, reaching 85% of US internet users in February 2007.
We estimate that the UK market for online ad networks doubled in size to around £120m during 2006, from £60 million in 2005. Spending on ad networks last year represented up to 25% of overall online display ad spend.
For more information about this sector, and profiles of 21 leading UK ad networks, see our Online Advertising Networks Buyer's Guide 2007 .