now reaches 26.9m unique users – almost 90% of the UK’s internet population - according to figures from comScore Media Metrix.

Its nearest rival is MediaBrokers, which reaches 22m uniques, 73.5% of the UK market. ValueClick reaches 68.4% of the UK’s internet users., 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