LONDON: Arguably the sole global constant these days is the rise and rise of internet advertising. And according to the latest forecasts from the London unit of ZentithOptimedia, expenditure in the online medium will overtake radio in 2008 - a year earlier than previously predicted.

The media-buying agency reports that online advertising worldwide rose 33% last year, topping $24.9 billion (€18.62bn; £12.58bn) compared with $18.7bn in 2005.

Adspend across all media formats grew fastest in the Middle East (+22.4%) and Eastern Europe, well ahead of North America (+5.2%) and Western Europe (+4%) where - to use the Zenith's euphemism - the ad markets are "maturing rapidly".

Over the forthcoming two years the biggest growth drivers in global adspend will be the US presidential elections and sporting events such as the Olympics and European soccer championships. After which ad bonanzas, revenues will dive Zenith warns.

Confounding fears that global TV advertising was headed for a long-term trough at the end of 2006, Zenith reports it is alive and well and set to be just 0.2 percentage points lower in 2009 than in 2005.

Data sourced from The Times (UK); additional content by WARC staff