Advertising.com 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.
ValueClick announced today that it has completed the integration of its vcmedia and Fastclick online advertising networks, creating a network with 59% reach among UK internet users.
The announcement, which follows the purchase of the US network Fastclick a year ago, is significant because it demonstrates the increasing competition in the ad networks space and the importance of reach as a selling point for the major players.