Internet advertising continues to gain on other ad categories.

ZenithOptimedia forecasts that global Internet advertising spending will grow by 28.2% in 2007, at the same time ad spending in other media will grow by only 3.9% — in other words, online ad spending will grow seven times faster.

This disparity speaks volumes about the ongoing seismic shift in the world of advertising. However, the shift to the Internet among US marketers is even more dramatic. eMarketer’s latest ad spending projections were released on Wednesday (see Internet Advertising Will Weather a Sluggish Economy). These put growth in US online ad spending at 18.9% in 2007, within an entire advertising industry set to grow by only 1.4%.

ZenithOptimedia also projects that the Internet’s share of world wide total ad spending will increase from 5.8% in 2006 to 8.6% in 2009.

The researcher’s data show worldwide spending on Internet advertising exceeding the amount spent outdoor advertising this year and surpassing even radio ad spending in 2009.

The analysts at ZenithOptimedia point out that the rise of Internet advertising has been dramatic. In terms of total ad spending, the Internet has overtaken two long-established media: cinema (which it overtook in 1997) and outdoor (which it overtook this year) in the space of only 11 years.

In addition, even in developed markets the Internet receives a much lower share of ad budgets than the amount of time consumers devote to it. ZenithOptimedia describes how, in 2005, consumers in the USA, Japan and the UK (the top three ad markets) spent 21.9% of their media time using the Internet, yet advertisers in those three markets spent only 6.8% of their budgets online.

ZenithOptimedia states: “We expect the Internet to take nearly 9% of global adspend by 2009, but experience from the most developed markets suggests it is heading for well over 10%. The Internet already attracts more than 10% of adspend in three markets (Norway, Sweden and the UK), and by 2009 we expect it to do so in ten markets (Australia, Canada, Israel, Japan, Norway, South Korea, Sweden, Taiwan, the UK and USA). The Internet has its highest share in the UK, where it will attract 13.5% of adspend this year and 21.5% in 2009.”

Looking at the breakdown of online advertising, the researchers found that paid search is the largest single type of Internet advertising, and the gap between search and display ads is widening. However, display includes video ads and other innovations that are exploiting the creative opportunities offered by high-speed broadband, and still has growth potential. Meanwhile, classified continues to migrate from print to online.

For another look into the future, read eMarketer’s US Online Ad Spending: Peak of Plateau? report.