Marketers worldwide will increase their spending in online ads at a 15 percent to 20 percent clip in the coming years, a growth rate that is "phenomenal," IDC said Wednesday.

This year, global spending in online ads will reach US$65.2 billion, or about 10 percent of the total advertising market.

As marketers continue to recognize the importance of promoting their goods and services online, they will increase their online ad budgets.

In 2011, online ad spending will hit $106.6 billion, accounting for almost 14 percent of the total advertising market, according to IDC.

Keyword-based search engine advertising will remain as the most popular online ad format through 2011, generating more than one third of the spending.

It will be followed by display ads, such as banners, with more than 20 percent, and classifieds, with almost 19 percent, according to IDC.

However, rich media ads, like those in video format, will see their spending grow very fast, at more than a 50 percent annual average rate.

The U.S. will lead all countries in online ad spending with $45 billion in 2011, but the fastest growing regions will be Central and Eastern Europe and Middle East and Africa with average annual growth rates of 42.1 percent and 29.8 percent respectively.

The region where online ads will have the largest portion of the total ad spending pie will be Western Europe, where marketers will devote 18.2 percent of their budgets to Internet ads in 2011. In Japan and the U.S. the percentages will be 16.3 percent and 14.6 percent respectively.

Today's leading categories of online ads-- adult content and gambling; information; electronics; and computing-- will continue as the top ones in 2011, IDC said.

In a related announcement, IDC reported that this year almost a quarter of the world's population-- 1.4 billion people-- will use the Internet on a regular basis, rising to 30 percent in 2012.

Today, the PC is the preferred device for accessing the Internet, but that will change in 2012, when it will be surpassed by mobile devices, IDC said.

The market researcher, which is owned by IDG News Service's parent company, also found that last year China became the country with the most Internet users, passing the U.S.