The agency says developing markets will largely dominate the scene, contributing to 61% of ad spend growth between 2012 and 2015, and increasing their share of global ad spend from 34% to 37%. Eurozone countries, however, will continue to experience troubled markets and will only grow slightly by 2015, Zenith admits, mainly due to the ongoing economic crisis in the region.

By medium: the internet remains the fastest-growing and Zenith forecasts 14%-15% annual growth for 2013 to 2015, due to the rapid rise of social media and online video advertising, each of which is growing at about 30% a year. The next biggest is television, which is forecast to contribute 39% of the growth by 2015, though it will fall back slightly, from 40.2% in 2012 to 40% in 2015.

However, print expenditure is tipped to shrink at an average of 1% a year with digital ads exceeding the combined total of newspaper and magazine advertising in 2015.

Steve King, global CEO for ZenithOptimedia Group, said: “Advertisers are willing to increase their budgets wherever they can achieve a strong return on investment. This means that developing markets, social media and online video are all growing rapidly, supporting continued expansion in global ad expenditure despite stagnation in the eurozone.”