In its earliest days, the web saw much of its growth coming from internet-based advertisers. Then, with the ad recovery over the last several years, the nation's largest advertisers moved more and more spending online.

Now comes the third wave: Smaller, often local advertisers kicking up their online spending. And in a big way.

The very smallest of advertisers will be driving the internet in the coming several years, and they will create a huge surge.

So says a new report from Britain’s Zenith Optimedia, out this morning, that predicts that global internet ad expenditures will rise 84 percent from 2005 to 2008, going from $18.57 billion last year to a projected $34.16 billion in 2008.

An increasing share of that growth will be driven by those smaller advertisers.

Most interesting, Zenith does not see the internet surge coming at the expense of other media, at least for these smaller advertisers.

Instead, advertisers will be ramping up spending, attracted by the web’s ability to deliver a very targeted audience, rather than shifting money from TV, magazines or radio.

It's already begun.

“Advertisers from smaller categories have been spending more than average on internet advertising, which is relatively cheap and can be targeted very effectively,” says the report. “This makes it suitable for smaller advertisers, for some of which mass-media campaigns would be too expensive and have too much wastage.”

Indeed, there’s evidence to back up this forecast.

A recent study released by Borrell Associates, a local media consulting group based in Portsmouth, Va., forecasts that local U.S. search will jump 31.6 percent in 2007, to $7.7 billion. That growth will be spurred mainly by local paid search advertising and email campaigns from smaller advertisers.

Indeed, small advertisers are more interested than ever in media that produce vertical and very trackable results. In a recent Media Life story on blog advertising, one media person observed, “I think this is the end of mass marketing.”

The most recent revenue numbers from the Interactive Advertising Bureau reveal smaller sites with correspondingly smaller advertisers are slowly starting to generate a greater share of online ad dollars.

Whereas during first half 2005, 96 percent of all web revenue was generated by the internet’s top 50 sites, according to the IAB, this year that number slipped slightly to 94 percent.

The Zenith report forecasts that internet will overtake out of home in share of advertising expenditures, at 5.7 to the latter’s 5.5 this year.

By 2008, online ad spending will account for 10 percent or more of ad expenditures in eight worldwide markets, including Australia, South Korea, Japan and the UK, where Zenith forecasts a share of 17.2 percent.